Directory of Researchers

SASAKI Daisuke
Graduate School of Science, Technology and Innovation / Department of Science, Technology and Innovation
Assistant Professor
Biology
Last Updated :2022/09/16

Researcher Profile and Settings

Affiliation

  • <Faculty / Graduate School / Others>

    Graduate School of Science, Technology and Innovation / Department of Science, Technology and Innovation
  • <Related Faculty / Graduate School / Others>

    Engineering Biology Research Center

Research Activities

Research Areas

  • Life sciences / Applied microbiology

Published Papers

  • Kengo Sasaki, Daisuke Sasaki, Katsunori Sasaki, Yuto Nishidono, Akihiro Yamamori, Ken Tanaka, Akihiko Kondo

    AbstractDaikenchuto (DKT) is a Japanese traditional herbal (Kampo) medicine containing ginseng, processed ginger, and Japanese or Chinese pepper. We aimed to determine how DKT affects human colonic microbiota. An in vitro microbiota model was established using fecal inocula collected from nine healthy volunteers, and each model was found to retain operational taxonomic units similar to the ones in the original human fecal samples. DKT was added to the in vitro microbiota model culture at a concentration of 0.5% by weight. Next-generation sequencing of bacterial 16S rRNA gene revealed a significant increase in the relative abundance of bacteria related to the Bifidobacterium genus in the model after incubation with DKT. In pure cultures, DKT significantly promoted the growth of Bifidobacterium adolescentis, but not that of Fusobacterium nucleatum or Escherichia coli. Additionally, in pure cultures, B. adolescentis transformed ginsenoside Rc to Rd, which was then probably utilized for its growth. Our study reveals the in vitro bifidogenic effect of DKT that likely contributes to its beneficial effects on the human colon.

    Springer Science and Business Media LLC, Dec. 2021, Scientific Reports, 11 (1), English

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Yota Tsuge, Masahiko Morita, Akihiko Kondo

    Abstract Background It is desirable to improve the anaerobic digestion processes of recalcitrant materials, such as cellulose. Enhancement of methane (CH4) production from organic molecules was previously accomplished through coupling a bioelectrochemical system (BES); however, scaling-up BES-based production is difficult. Here, we developed a two-stage process consisting of a BES using low-cost and low-reactive carbon sheets as the cathode and anode, and a fixed film reactor (FFR) containing conductive material, i.e., carbon fiber textiles (CFTs) (:BES → FFR). By controlling the cathodic current at 2.7 μA/cm2 without abiotic H2 production, the three-electrode BES system was operated to mimic a microbial electrolysis cell. Results The thermophilic BES (inlet pH: 6.1) and FFR (inlet pH: 7.5) were operated using hydraulic retention times (HRTs) of 2.5 and 4.2 days, respectively, corresponding to a cellulose load of 3555.6 mg-carbon (C)/(L day). The BES → FFR process achieved a higher CH4 yield (37.5%) with 52.8 vol% CH4 in the product gas compared to the non-bioelectrochemical system (NBES) → FFR process, which showed a CH4 yield of 22.1% with 46.8 vol% CH4. The CH4 production rate (67.5 mM/day) obtained with the BER → FFR process was much higher than that obtained using electrochemical methanogenesis (0.27 mM/day). Application of the electrochemical system or CFTs improved the yields of CH4 with the NBES → FFR or BES → non-fixed film reactor process, respectively. Meta 16S rRNA sequencing revealed that putative cellulolytic bacteria (identified as Clostridium species) were present in the BES and NBES, and followed (BES→ and NBES→) FFR. Notably, H2-consuming methanogens, Methanobacterium sp. and Methanosarcina sp., showed increased relative abundances in the suspended fraction and attached fraction of (BES→) FFR, respectively, compared to that of (NBES→) FFR, although these methanogens were observed at trace levels in the BES and NBES. Conclusions These results indicate that bioelectrochemical preprocessing at a low current effectively induces interspecies H2 transfer in the FFR with conductive material. Sufficient electrochemical preprocessing was observed using a relatively short HRT. This type of two-stage process, BES → FFR, is useful for stabilization and improvement of the biogas (CH4) production from cellulosic material, and our results imply that the two-stage system developed here may be useful with other recalcitrant materials.

    Springer Science and Business Media LLC, Dec. 2021, Biotechnology for Biofuels, 14 (1)

    Scientific journal

  • Naofumi Yoshida, Tomoya Yamashita, Tatsunori Osone, Tetsuya Hosooka, Masakazu Shinohara, Seiichi Kitahama, Kengo Sasaki, Daisuke Sasaki, Takeshi Yoneshiro, Tomohiro Suzuki, Takuo Emoto, Yoshihiro Saito, Genki Ozawa, Yushi Hirota, Yasuyuki Kitaura, Yoshiharu Shimomura, Yuko Okamatsu-Ogura, Masayuki Saito, Akihiko Kondo, Shingo Kajimura, Takeshi Inagaki, Wataru Ogawa, Takuji Yamada, Ken-ichi Hirata

    Elsevier BV, Nov. 2021, iScience, 24 (11), 103342 - 103342, English

    Scientific journal

  • Namiko Hoshi, Jun Inoue, Daisuke Sasaki, Kengo Sasaki

    The human gut harbors a complex microbial community that performs a range of metabolic, physiological, and immunological functions. The host and its inhabiting microorganisms are often referred to as a "superorganism." Dysbiosis of gut microflora has been associated with the pathogenesis of intestinal disorders including inflammatory bowel disease, colorectal cancer, and extra-intestinal disorders such as cardiovascular disease. Therefore, gut microbiome interventions are important for the prevention and treatment of diseases. However, ethical, economic, scientific, and time constraints limit the outcome of human intervention or animal studies targeting gut microbiota. We recently developed an in vitro batch fermentation model (the Kobe University Human Intestinal Microbiota Model, KUHIMM) that is capable of hosting a majority of gut microbial species in humans and also detects the metabolites produced by microorganisms in real time. In this mini review, we elucidated the characteristics of the KUHIMM and its applicability in analyzing the effect of diet, drugs, probiotics, and prebiotics on intestinal bacteria. In addition, we introduce as examples its application to disease models, such as ulcerative colitis, in which intestinal bacteria are intricately involved in the process of pathogenesis. We also discuss the potential of the KUHIMM in precision medicine. KEY POINTS: • In vitro gut fermentation model to simulate human colonic microbiota • Screening of potential prebiotics and probiotic candidates in healthy model • Construction of disease models of ulcerative colitis and coronary artery disease.

    Springer Science and Business Media LLC, Apr. 2021, Applied Microbiology and Biotechnology, 105 (7), 2625 - 2632, English, International magazine

    Scientific journal

  • Kengo Sasaki, Tomoyuki Mori, Namiko Hoshi, Daisuke Sasaki, Jun Inoue, Reiko Shinkura, Akihiko Kondo

    Abstract W27 monoclonal immunoglobulin A (IgA) suppresses pathogenic Escherichia coli cell growth; however its effect on the human intestine remains unclear. We thus aimed to determine how W27 IgA affects the human colonic microbiota using the in vitro microbiota model. This model was established using fecal samples collected from 12 healthy volunteers; after anaerobic cultivation, each model was found to retain the genera found in the original human fecal samples. After pre-incubating W27 IgA with the respective fecal sample in aerobic condition, the mixture of W27 IgA (final concentration, 0.5 µg/mL) and each fecal sample was added to the in vitro microbiota model and cultured under anaerobic condition,. Next-generation sequencing of the bacterial 16S rRNA gene revealed that W27 IgA addition significantly decreased the relative abundance of bacteria related to the genus Escherichia in the model. Additionally, at a final concentration of 5 µg/mL, W27 IgA delayed growth in pure culture of Escherichia coli isolated from human fecal samples. Our study thus revealed the suppressive effect of W27 IgA on the genus Escherichia at relatively low-concentrations and the usefulness of an in vitro microbiota model to evaluate the effect of IgA as a gut microbiota regulator.

    Research Square, 03 Mar. 2021, English

  • Ayaka Nakashima, Kengo Sasaki, Daisuke Sasaki, Kosuke Yasuda, Kengo Suzuki, Akihiko Kondo

    AbstractThe alga Euglena gracilis (E. gracilis) has recently gained attention as a health food, but its effects on human gut microbiota remain unknown. This study aimed to determine the effect of E. gracilis on gut microbiota and defecation due to modulation of microbiota composition in vitro and in vivo. The in vitro model simulating human colonic microbiota revealed that E. gracilis addition stimulated the growth of commensal Faecalibacterium. Further, E. gracilis addition enhanced butyrate production by Faecalibacterium prausnitzii. Paramylon, an insoluble dietary fibre that accumulates in E. gracilis and is the main component of E. gracilis, did not stimulate Faecalibacterium growth in vitro. Daily ingestion of 2 g of E. gracilis for 30 days increased bowel movement frequency as well as stool volume in 28 human participants. Collectively, these findings indicate that E. gracilis components other than paramylon, stimulate the growth of Faecalibacterium to improve digestive health as well as promote defecation by increasing butyrate production.

    Springer Science and Business Media LLC, Jan. 2021, Scientific Reports, 11 (1), English

    Scientific journal

  • Naofumi Yoshida, Tomoya Yamashita, Shigenobu Kishino, Hikaru Watanabe, Kengo Sasaki, Daisuke Sasaki, Tokiko Tabata, Yuta Sugiyama, Nahoko Kitamura, Yoshihiro Saito, Takuo Emoto, Tomohiro Hayashi, Tomoya Takahashi, Masakazu Shinohara, Ro Osawa, Akihiko Kondo, Takuji Yamada, Jun Ogawa, Ken-ichi Hirata

    Springer Science and Business Media LLC, Dec. 2020, Scientific Reports, 10 (1), 13009, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Asuka Hannya, Jun Tsubota, Akihiko Kondo

    Springer Science and Business Media LLC, Dec. 2020, Scientific Reports, 10 (1), 8516, English

    [Refereed]

    Scientific journal

  • Shunsuke Oba, Tadahiro Sunagawa, Reiko Tanihiro, Kyoko Awashima, Hiroshi Sugiyama, Tetsuji Odani, Yasunori Nakamura, Akihiko Kondo, Daisuke Sasaki, Kengo Sasaki

    Abstract Yeast mannan (YM) is an indigestible water-soluble polysaccharide of the yeast cell wall, with a notable prebiotic effect on the intestinal microbiota. We previously reported that YM increased Bacteroides thetaiotaomicron abundance in in vitro rat faeces fermentation, concluding that its effects on human colonic microbiota should be investigated. In this study, we show the effects of YM on human colonic microbiota and its metabolites using an in vitro human faeces fermentation system. Bacterial 16S rRNA gene sequence analysis showed that YM administration did not change the microbial diversity or composition. Quantitative real-time PCR analysis revealed that YM administration significantly increased the relative abundance of Bacteroides ovatus and B. thetaiotaomicron. Moreover, a positive correlation was observed between the relative ratio (with or without YM administration) of B. thetaiotaomicron and B. ovatus (r = 0.92), suggesting that these bacteria utilise YM in a coordinated manner. In addition, YM administration increased the production of acetate, propionate, and total short-chain fatty acids. These results demonstrate the potential of YM as a novel prebiotic that selectively increases B. thetaiotaomicron and B. ovatus and improves the intestinal environment. The findings also provide insights that might be useful for the development of novel functional foods.

    Springer Science and Business Media LLC, Oct. 2020, Scientific Reports, 10 (1), 17351, English

    Scientific journal

  • Katsuki Murai, Daisuke Sasaki, Shunsuke Kobayashi, Akira Yamaguchi, Hiroto Uchikura, Tomokazu Shirai, Kengo Sasaki, Akihiko Kondo, Yota Tsuge

    Glucose is metabolized through central metabolic pathways such as glycolysis and the pentose phosphate pathway (PPP) to synthesize downstream metabolites including amino acids. However, how the split ratio of carbon flux between glycolysis and PPP specifically affects the formation of downstream metabolites remains largely unclear. Here, we conducted a comprehensive metabolomic analysis to investigate the effect of the split ratio between glycolysis and the PPP on the intracellular concentration of amino acids and their derivatives in Corynebacterium glutamicum. The split ratio was varied by exchanging the promoter of a gene encoding glucose 6-phosphate isomerase (PGI). The ratio was correlated with the pgi transcription level and the enzyme activity. Concentrations of threonine and lysine-derivative 1,5-diaminopentane increased with an increase of the split ratio into the PPP. In contrast, concentrations of alanine, leucine, and valine were increased with an increase of the split ratio into glycolysis. These results could provide a new engineering target for improving the production of the amino acids and the derivatives.

    17 Jul. 2020, ACS synthetic biology, 9 (7), 1615 - 1622, English, International magazine

    [Refereed]

    Scientific journal

  • Effective bifidogenic growth factors cyclo-Val-Leu and cyclo-Val-Ile produced by Bacillus subtilis C-3102 in the human colonic microbiota model

    Misaki Hatanaka, Hiroto Morita, Yumi Aoyagi, Kengo Sasaki, Daisuke Sasaki, Akihiko Kondo, Teppei Nakamura

    May 2020, Scientific Reports, 10, 7591, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Jun Inoue, Namiko Hoshi, Takayuki Maeda, Ryouichi Yamada, Akihiko Kondo

    The aim of this study was to clarify the effect of the spore-forming and lactic acid-producing probiotic strain, Bacillus coagulans SANK 70258, on human colonic microbiota of healthy subjects and ulcerative colitis patients. A model culture system was employed to construct the in vitro human colonic microbiota, to retain the bacterial species richness and simulate the patient's disordered composition, from the fecal inoculum. Bacterial 16S rRNA gene sequencing confirmed that administration of B. coagulans SANK 70258 (at an initial concentration of 4 × 107-total cells/mL) suppressed bacteria related to the family Enterobacteriaceae in the microbiota models for both healthy subjects (P = 0.016) and ulcerative colitis patients (P = 0.023). In addition, administration of B. coagulans SANK 70258 increased bacteria related to the family Lachnospiraceae (P = 0.031), thereby enhancing butyrate production (P = 0.031) in the microbiota models of healthy subjects. However, these changes were not observed in the microbiota models of ulcerative colitis patients, likely owing to the low abundance of Lachnospiraceae species. This study demonstrates the potential of B. coagulans SANK 70258 to exhibit antimicrobial activity against harmful organisms in patients with ulcerative colitis, while improving the intestinal microenvironment by increasing butyrogenesis in healthy persons. KEY POINTS: • B. coagulans SANK 70258 treatment reduced colonic Enterobacteriaceae species. • B. coagulans SANK 70258 treatment enhanced butyrogenesis in healthy individuals. • B. coagulans SANK 70258 treatment increased Lachnospiraceae in healthy persons. • B. coagulans SANK 70258 improves the colonic microenvironment in ulcerative colitis.

    07 Mar. 2020, Applied microbiology and biotechnology, English, International magazine

    [Refereed]

  • Bifidogenic and butyrogenic effects of young barely leaf extract in an in vitro human colonic microbiota model

    Daisuke Sasaki, Kengo Sasaki, Yasushi Kadowaki, Yasuyuki Aotsuka, Akihiko Kondo

    Nov. 2019, AMB Express, 9, 182, English

    [Refereed]

    Scientific journal

  • Butyryl-CoA:acetate CoA-transferase gene associated with the genus Roseburia is decreased in the gut microbiota of Japanese patients with ulcerative colitis

    Ryohei Shinohara, Kengo Sasaki, Jun Inoue, Namiko Hoshi, Itsuko Fukuda, Daisuke Sasaki, Akihiko Kondo, Ro Osawa

    Oct. 2019, Bioscience of Microbiota, Food and Health, 38 (4), 159 - 163, English

    [Refereed]

    Scientific journal

  • Naofumi Yoshida, Kengo Sasaki, Daisuke Sasaki, Tomoya Yamashita, Hajime Fukuda, Tomohiro Hayashi, Tokiko Tabata, Ro Osawa, Ken-Ichi Hirata, Akihiko Kondo

    AIM: Bacteroides vulgatus and B. dorei have a protective effect against atherosclerosis, suggesting that expansion of these species in the gut microbiota could help patients with coronary artery disease (CAD). This study aimed to investigate the effect of resistant starch (RS) on the gut microbiota and its metabolites in fecal sample cultures from patients with CAD and individuals without CAD, using a single-batch fermentation system. METHODS: Fecal samples from 11 patients with CAD and 10 individuals without CAD were fermented for 30 h with or without RS in the Kobe University Human Intestinal Microbiota Model (KUHIMM). Gut microbiota and the abundance of B. vulgatus and B. dorei were analyzed using 16S ribosomal ribonucleic acid (rRNA) gene sequencing and the quantitative polymerase chain reaction. Short-chain fatty acids were analyzed using high-performance liquid chromatography. RESULTS: Gut microbial analysis showed significantly lower levels of B. vulgatus and B. dorei in the original fecal samples from patients with CAD, which was simulated after 30 h of fermentation in the KUHIMM. Although RS significantly increased the absolute numbers of B. vulgatus and B. dorei, and butyrate levels in CAD fecal sample cultures, the numbers varied among each patient. CONCLUSIONS: The effect of RS on gut microbiota and its metabolites in the KUHIMM varied between CAD and non-CAD fecal sample cultures. The KUHIMM may be useful for preclinical evaluations of the effects of RS on the gut microbiota and its metabolites.

    01 Aug. 2019, Journal of atherosclerosis and thrombosis, 26 (8), 705 - 719, English, Domestic magazine

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Jun Inoue, Daisuke Sasaki, Namiko Hoshi, Tomokazu Shirai, Itsuko Fukuda, Takeshi Azuma, Akihiko Kondo, Ro Osawa

    May 2019, Biotechnology Journal, 14, 1800555, English

    [Refereed]

    Scientific journal

  • Sustainable production of glutathione from lignocellulose-derived sugars using engineered Saccharomyces cerevisiae

    KOBAYASHI Jyumpei, SASAKI Daisuke, BAMBA Takahiro, HASUNUMA Tomohisa, KONDO Akihiko

    Feb. 2019, Applied Microbiology and Biotechnology, 103 (3), 1243 - 1254, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Yota Tsuge, Akihiko Kondo

    Background: Using a microbial fuel cell (MFC), we observed that a complex microbial community decomposed starch and transferred electrons to a graphite felt anode to generate current. In spite of the same reactor configuration, inoculum, substrate, temperature, and pH, MFCs produced different current and power density. To understand which factor(s) affected electricity generation, here, we analyzed a complex microbial community in an anodic biofilm and fermentation broth using Illumina MiSeq sequencing and metabolomics. Results: Microbial biomass on the anode was lower in MFCs generating more electricity (0.09-0.16 mg cm-2-anode) than in those generating less electricity (0.60-2.80 mg cm-2-anode), while being equal (3890-4196 mg L-1-broth) in the fermentation broth over the same operational period. Chemical oxygen demand removal and acetate concentration were also similar in fermentation broths. MFCs generating more electricity had relatively more exoelectrogenic bacteria, such as Geobacter sp., but fewer acetate-utilizing Methanosarcina sp. and/or Lactococcus sp. in anodic biofilms. Accordingly, anodic biofilms generating more electricity presented higher levels of most intracellular metabolites related to the tricarboxylic acid cycle and a higher intracellular ATP/ADP ratio, but a lower intracellular NADH/NAD+ ratio. Moreover, the level of intracellular glutamate, an essential metabolite for microbial anabolic reactions, correlated negatively with current density. Conclusion: Microbial growth on the anode and intracellular glutamate levels negatively affect electricity generation by MFCs. Reduced formation of anodic biofilm, in which intracellular glutamate concentration is 33.9 μmol g-cell-1 or less, favors the growth of acetate-utilizing Geobacter sp. on the anode and improves current generation.

    2019, Biotechnology for biofuels, 12, 72 - 72, English, International magazine

    [Refereed]

    Scientific journal

  • Widespread effect of N-acetyl-D-glucosamine assimilation on the metabolisms of amino acids, purines, and pyrimidines in Scheffersomyces stipitis

    INOKUMA Kentaro, MATSUDA Mami, SASAKI Daisuke, HASUNUMA Tomohisa, KONDO Akihiko

    Sep. 2018, Microbial Cell Factories, 17, 153, English

    [Refereed]

    Scientific journal

  • A procedure for precise determination of glutathione produced by Saccharomyces cerevisiae

    KOBAYASHI Jyumpei, SASAKI Daisuke, KONDO Akihiko

    Jun. 2018, Bio-protocol, 8 (12), e2887, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Kazuhide Kamiya, Shuji Nakanishi, Akihiko Kondo, Souichiro Kato

    Microbial electrochemical systems (MESs) are expected to be put into practical use as an environmental technology that can support a future environmentally friendly society. However, conventional MESs present a challenge of inevitably increasing initial investment, mainly due to requirements for a large numbers of electrode assemblies. In this review, we introduce electrochemical biotechnologies that are under development and can minimize the required electrode assemblies. The novel biotechnologies, called electro-fermentation and indirect electro-stimulation, can drive specific microbial metabolism by electrochemically controlling intercellular and extracellular redox states, respectively. Other technologies, namely electric syntrophy and microbial photo-electrosynthesis, obviate the need for electrode assemblies, instead stimulating targeted reactions by using conductive particles to create new metabolic electron flows.

    Apr. 2018, Current opinion in biotechnology, 50, 182 - 188, English, International magazine

    [Refereed]

    Scientific journal

  • Low amounts of dietary fibre increase in vitro production of short-chain fatty acids without changing human colonic microbiota structure

    Daisuke Sasaki, Kengo Sasaki, Naoko Ikuta, Takahiro Yasuda, FUKUDA ITSUKO, Akihiko Kondo, Ro Osawa

    Jan. 2018, Scientific Reports, 8, 435, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Yota Tsuge, Masahiko Morita, Akihiko Kondo

    Background: Bioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. We examined the feasibility of applying a BES to dark hydrogen fermentation and its effects on a two-stage fermentation process comprising hydrogen and methane production. The BES used low-cost, low-reactivity carbon sheets as the cathode and anode, and the cathodic potential was controlled at - 1.0 V (vs. Ag/AgCl) with a potentiostat. The operation used 10 g/L glucose as the major carbon source. Results: The electric current density was low throughout (0.30-0.88 A/m2 per electrode corresponding to 0.5-1.5 mM/day of hydrogen production) and water electrolysis was prevented. At a hydraulic retention time of 2 days with a substrate pH of 6.5, the BES decreased gas production (hydrogen and carbon dioxide contents: 52.1 and 47.1%, respectively), compared to the non-bioelectrochemical system (NBES), although they had similar gas compositions. In addition, a methane fermenter (MF) was applied after the BES, which increased gas production (methane and carbon dioxide contents: 85.1 and 14.9%, respectively) compared to the case when the MF was applied after the NBES. Meta 16S rRNA sequencing revealed that the BES accelerated the growth of Ruminococcus sp. and Veillonellaceae sp. and decreased Clostridium sp. and Thermoanaerobacterium sp., resulting in increased propionate and ethanol generation and decreased butyrate generation; however, unknowingly, acetate generation was increased in the BES. Conclusions: The altered redox potential in the BES likely transformed the structure of the microbial consortium and metabolic pattern to increase methane production and decrease carbon dioxide production in the two-stage process. This study showed the utility of the BES to act on the microbial consortium, resulting in improved gas production from carbohydrate compounds.

    2018, Biotechnology for biofuels, 11, 173 - 173, English, International magazine

    [Refereed]

    Scientific journal

  • Kiyotaka Y. Hara, Jyumpei Kobayashi, Ryosuke Yamada, Daisuke Sasaki, Yuki Kuriya, Yoko Hirono-Hara, Jun Ishii, Michihiro Araki, Akihiko Kondo

    Biomass resources are attractive carbon sources for bioproduction because of their sustainability. Many studies have been performed using biomass resources to produce sugars as carbon sources for cell factories. Expression of biomass hydrolyzing enzymes in cell factories is an important approach for constructing biomass-utilizing bioprocesses because external addition of these enzymes is expensive. In particular, yeasts have been extensively engineered to be cell factories that directly utilize biomass because of their manageable responses to many genetic engineering tools, such as gene expression, deletion and editing. Biomass utilizing bioprocesses have also been developed using these genetic engineering tools to construct metabolic pathways. However, sugar input and product output from these cells are critical factors for improving bioproduction along with biomass utilization and metabolic pathways. Transporters are key components for efficient input and output activities. In this review, we focus on transporter engineering in yeast to enhance bioproduction from biomass resources.

    OXFORD UNIV PRESS, Nov. 2017, FEMS YEAST RESEARCH, 17 (7), fox061, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Hideo Kawaguchi, Masahiro Yasukawa, Daisuke Sasaki, Takashi Sazuka, Eiji Kamio, Chiaki Ogino, Hideto Matsuyama, Akihiko Kondo

    The juice from sweet sorghum cultivar SIL-05 (harvested at physiological maturity) was extracted, and the component sucrose and reducing sugars (such as glucose and fructose) were subjected to a membrane separation process to purify the sucrose for subsequent sugar refining and to obtain a feedstock for repeated bioethanol production. Nanofiltration (NF) of an ultrafiltration (UF) permeate using an NTR-7450 membrane (Nitto Denko Corporation, Osaka, Japan) concentrated the juice and produced a sucrose-rich fraction (143.2 g L-1 sucrose, 8.5 g L-1 glucose, and 4.5 g L-1 fructose). In addition, the above NF permeate was concentrated using an ESNA3 NF membrane to provide concentrated permeated sugars (227.9 g L-1) and capture various amino acids in the juice, enabling subsequent ethanol fermentation without the addition of an exogenous nitrogen source. Sequential batch fermentation using the ESNA3 membrane concentrate provided an ethanol titer and theoretical ethanol yield of 102.5-109.5 g L-1 and 84.4-89.6%, respectively, throughout the five-cycle batch fermentation by Saccharomyces cerevisiae BY4741. Our results demonstrate that a membrane process using UF and two types of NF membranes has the potential to allow sucrose purification and repeated bioethanol production.

    Aug. 2017, Applied microbiology and biotechnology, 101 (15), 6007 - 6014, English, International magazine

    [Refereed]

    Scientific journal

  • Jyumpei Kobayashi, Daisuke Sasaki, Kiyotaka Y. Hara, Tomohisa Hasunuma, Akihiko Kondo

    Background: Oxidized glutathione (GSSG) is the preferred form for industrial mass production of glutathione due to its high stability compared with reduced glutathione (GSH). In our previous study, over-expression of the mitochondrial thiol oxidase ERV1 gene was the most effective for high GSSG production in Saccharomyces cerevisiae cells among three types of different thiol oxidase genes. Results: We improved Erv1 enzyme activity for oxidation of GSH and revealed that S32 and N34 residues are critical for the oxidation. Five engineered Erv1 variant proteins containing S32 and/or N34 replacements exhibited 1.7- to 2.4-fold higher in vitro GSH oxidation activity than that of parental Erv1, whereas the oxidation activities of these variants for gamma-glutamylcysteine were comparable. According to three-dimensional structures of Erv1 and protein stability assays, S32 and N34 residues interact with nearby residues through hydrogen bonding and greatly contribute to protein stability. These results suggest that increased flexibility by amino acid replacements around the active center decrease inhibitory effects on GSH oxidation. Over-expressions of mutant genes coding these Erv1 variants also increased GSSG and consequently total glutathione production in S. cerevisiae cells. Over-expression of the ERV1(S32A) gene was the most effective for GSSG production in S. cerevisiae cells among the parent and other mutant genes, and it increased GSSG production about 1.5-fold compared to that of the parental ERV1 gene. Conclusions: This is the first study demonstrating the pivotal effects of S32 and N34 residues to high GSH oxidation activity of Erv1. Furthermore, in vivo validity of Erv1 variants containing these S32 and N34 replacements were also demonstrated. This study indicates potentials of Erv1 for high GSSG production.

    BIOMED CENTRAL LTD, Mar. 2017, MICROBIAL CELL FACTORIES, 16, 44, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Naoko Okai, Kosei Tanaka, Ryohei Nomoto, Itsuko Fukuda, Ken-Ichi Yoshida, Akihiko Kondo, Ro Osawa

    Accumulating evidence suggests that dietary taurine (2-aminoethanesulfonic acid) exerts beneficial anti-inflammatory effects in the large intestine. In this study, we investigated the possible impact of taurine on human colonic microbiota using our single-batch fermentation system (Kobe University Human Intestinal Microbiota Model; KUHIMM). Fecal samples from eight humans were individually cultivated with and without taurine in the KUHIMM. The results showed that taurine remained largely undegraded after 30 h of culturing in the absence of oxygen, although some 83% of the taurine was degraded after 30 h of culturing under aerobic conditions. Diversity in bacterial species in the cultures was analyzed by 16S rRNA gene sequencing, revealing that taurine caused no significant change in the diversity of the microbiota; both operational taxonomic unit and Shannon-Wiener index of the cultures were comparable to those of the respective source fecal samples. In addition, principal coordinate analysis indicated that taurine did not alter the composition of bacterial species, since the 16S rRNA gene profile of bacterial species in the original fecal sample was maintained in each of the cultures with and without taurine. Furthermore, metabolomic analysis revealed that taurine did not affect the composition of short-chain fatty acids produced in the cultures. These results, under these controlled but artificial conditions, suggested that the beneficial anti-inflammatory effects of dietary taurine in the large intestine are independent of the intestinal microbiota. We infer that dietary taurine may act directly in the large intestine to exert anti-inflammatory effects.

    2017, PloS one, 12 (7), e0180991, English, International magazine

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Yota Tsuge, Akihiko Kondo

    The metabolic state of microflora (mixed microbial cultures) in microbial fuel cells (MFCs) is currently unclear. Metabolomic analyses were conducted of microflora growing on the anodic electrodes of MFCs operated at pH 7.0, 5.5, or 4.0 and utilizing starch as the major carbon substrate. A much higher current was produced at pH 7.0 than at pH 5.5 and 4.0, correlating with an increased population ratio of Geobacter species to the total bacteria growing on the electrode. Most intracellular metabolites related to the tricarboxylic acid (TCA) cycle were present at a higher level at pH 7.0 than at pH 5.5 and 4.0, and the levels of metabolites correlated well with the obtained current densities. A high intracellular adenosine triphosphate (ATP)/adenosine diphosphate (ADP) ratio at pH 7.0, compared to at pH 5.5 and 4.0, likewise supported current production. Overall, the metabolomic analyses demonstrated that activation of the TCA cycle and increased ATP generation are critical parameters for electricity generation by microflora.

    BIOMED CENTRAL LTD, Dec. 2016, AMB EXPRESS, 6, 125, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Mami Okamoto, Tomokazu Shirai, Yota Tsuge, Ayami Fujino, Daisuke Sasaki, Masahiko Morita, Fumio Matsuda, Jun Kikuchi, Akihiko Kondo

    Rice straw was mechanically milled using a process consuming 1.9 MJ/kg-biomass, and 10 g/L of unmilled or milled rice straw was used as the carbon source for methane fermentation in a digester containing carbon fiber textile as the supporting material. Milling increased methane production from 226 to 419 mL/L/day at an organic loading rate of 2180 mg-dichromate chemical oxygen demand/L/day, corresponding to 260 mL(CH4/gVS). Storage of the fermentation effluent at room temperature decreased the weight of the milled rice straw residue from 3.81 to 1.00 g/L. The supernatant of the effluent was subjected to nanofiltration. The black concentrates deposited on the nanofiltration membranes contained 53.0-57.9% lignin. Solution nuclear magnetic resonance showed that lignin aromatic components such as p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) were retained primarily, and major lignin interunit structures such as the beta-O-4-H/G unit were absent. This combinational process will aid the complete utilization of rice straw. (C) 2016 Published by Elsevier Ltd.

    ELSEVIER SCI LTD, Sep. 2016, BIORESOURCE TECHNOLOGY, 216, 830 - 837, English

    [Refereed]

    Scientific journal

  • Keisuke Yamamoto, Kiyotaka Y. Hara, Toshihiko Morita, Akira Nishimura, Daisuke Sasaki, Jun Ishii, Chiaki Ogino, Noriyuki Kizaki, Akihiko Kondo

    Background: Red yeast, Xanthophyllomyces dendrorhous is the only yeast known to produce astaxanthin, an antioxidant isoprenoid (carotenoid) widely used in the aquaculture, food, pharmaceutical and cosmetic industries. The potential of this microorganism as a platform cell factory for isoprenoid production has been recognized because of high flux through its native terpene pathway. Recently, we developed a multiple gene expression system in X. dendrorhous and enhanced the mevalonate synthetic pathway to increase astaxanthin production. In contrast, the mevalonate synthetic pathway is suppressed by ergosterol through feedback inhibition. Therefore, releasing the mevalonate synthetic pathway from this inhibition through the deletion of genes involved in ergosterol synthesis is a promising strategy to improve isoprenoid production. An efficient method for deleting diploid genes in X. dendrorhous, however, has not yet been developed. Results: Xanthophyllomyces dendrorhous was cultivated under gradually increasing concentrations of antibiotics following the introduction of antibiotic resistant genes to be replaced with target genes. Using this method, double CYP61 genes encoding C-22 sterol desaturases relating to ergosterol biosynthesis were deleted sequentially. This double CYP61 deleted strain showed decreased ergosterol biosynthesis compared with the parental strain and single CYP61 disrupted strain. Additionally, this double deletion of CYP61 genes showed increased astaxanthin production compared with the parental strain and the single CYP61 knockout strain. Finally, astaxanthin production was enhanced by 1.4-fold compared with the parental strain, although astaxanthin production was not affected in the single CYP61 knockout strain. Conclusions: In this study, we developed a system to completely delete target diploid genes in X. dendrorhous. Using this method, we deleted diploid CYP61 genes involved in the synthesis of ergosterol that inhibits the pathway for mevalonate, which is a common substrate for isoprenoid biosynthesis. The resulting decrease in ergosterol biosynthesis increased astaxanthin production. The efficient method for deleting diploid genes developed in this study has the potential to improve industrial production of various isoprenoids in X. dendrorhous.

    BIOMED CENTRAL LTD, Sep. 2016, MICROBIAL CELL FACTORIES, 15 (1), 155, English

    [Refereed]

    Scientific journal

  • Risa Takagi, Kengo Sasaki, Daisuke Sasaki, Itsuko Fukuda, Kosei Tanaka, Ken-ichi Yoshida, Akihiko Kondo, Ro Osawa

    We devised a single-batch fermentation system to simulate human colonic microbiota from fecal samples, enabling the complex mixture of microorganisms to achieve densities of up to 1011 cells/mL in 24 h. 16S rRNA gene sequence analysis of bacteria grown in the system revealed that representatives of the major phyla, including Bacteroidetes, Firmicutes, and Actinobacteria, as well as overall species diversity, were consistent with those of the original feces. On the earlier stages of fermentation (up to 9 h), trace mixtures of acetate, lactate, and succinate were detectable; on the later stages (after 24 h), larger amounts of acetate accumulated along with some of propionate and butyrate. These patterns were similar to those observed in the original feces. Thus, this system could serve as a simple model to simulate the diversity as well as the metabolism of human colonic microbiota. Supplementation of the system with several prebiotic oligosaccharides (including fructo-, galacto-, isomalto-, and xylo-oligosaccharides; lactulose; and lactosucrose) resulted in an increased population in genus Bifidobacterium, concomitant with significant increases in acetate production. The results suggested that this fermentation system may be useful for in vitro, preclinical evaluation of the effects of prebiotics prior to testing in humans.

    PUBLIC LIBRARY SCIENCE, Aug. 2016, PLOS ONE, 11 (8), e0160533, English

    [Refereed]

    Scientific journal

  • Jieun Song, Daisuke Sasaki, Kengo Sasaki, Souichiro Kato, Akihiko Kondo, Kazuhito Hashimoto, Shuji Nakanishi

    Comprehensive metabolomic analysis of anode-respiring Geobacter sulfurreducens cells revealed that intracellular levels of metabolites related to the tricarboxylic acid (TCA) cycle, gluconeogenesis, consumptions of nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH), and adenosine triphosphate (ATP) generation correlated well with the activity of microbial anode-respiration detected as microbial electric current. Use of a glassy carbon electrode as the anode material in a three-electrode system resulted in a higher microbial current at +0.2 V (vs. Ag/AgCl) than at -0.2 V. A larger current flow resulted in higher concentrations of TCA cycle metabolites and lower concentrations of gluconeogenesis metabolites. Metabolomic analysis also revealed that higher anode respiration activity resulted in a higher ATP/adenosine diphosphate (ADP) ratio and lower ratios of NADH/NAD(+) and NADPH/NADP(+). These findings provide direct experimental evidence that microbial anode-respiration activity controlled by the anode potential influences both the flux of central metabolic pathways and the redox balance in microbial fuel cells. (C) 2015 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Jan. 2016, PROCESS BIOCHEMISTRY, 51 (1), 34 - 38, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Daisuke Sasaki, Hideo Kawaguchi, Takashi Sazuka, Chiaki Ogino, Akihiko Kondo

    Sequential batch fermentation from sweet sorghum juice concentrated by membrane separation (ultrafiltration permeation and nanofiltration concentration) to increase sugar contents, was investigated. Ethanol production at 5th batch fermentation by Saccharomyces cerevisiae BY4741 attained 113.7 +/- 3.1 g L-1 (89.1 +/- 2.2% of the theoretical ethanol yield) from 270.0 +/- 22.6 g L-1 sugars, corresponding to 98.7% of ethanol titer attained at the 1st batch fermentation. This titer was comparable to ethanol production of 115.8 +/- 0.6 g L-1 (87.1 +/- 2.7% of the theoretical ethanol yield) obtained at 5th batch fermentation with 3 g L-1 yeast extract and 6 g L-1 polypeptone. Increase of cell density in the concentrated sweet sorghum juice was observed during sequential batch fermentation, as indicated by increased OD600. Utilization of sweet sorghum juice as the sole source, membrane separation, and S. cerevisiae was a cost-effective process for high ethanol production. (C) 2015 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Jun. 2015, BIORESOURCE TECHNOLOGY, 186, 351 - 355, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Mami Okamoto, Tomokazu Shirai, Yota Tsuge, Hiroshi Teramura, Daisuke Sasaki, Hideo Kawaguchi, Tomohisa Hasunuma, Chiaki Ogino, Fumio Matsuda, Jun Kikuchi, Akihiko Kondo

    Background: Hydrothermal pretreatment of lignocellulosic biomass such as rice straw can dissolve part of the lignin and hemicellulose into a liquid fraction, thus facilitating enzyme accessibility to cellulose in bioethanol production process. Lignin is awaited to be recovered after hydrothermal pretreatment for utilization as value-added chemical, and lignin recovery also means removal of fermentation inhibitors. To recover lignin with high content from the liquid fraction, it is necessary to separate lignin and hemicellulose-derived polysaccharide. Therefore, the following processes were applied: membrane separation with nanofiltration (NF) and enzymatic hydrolysis by hemicellulase. To clarify lignin-concentrated fraction obtained during these processes, the fates of lignin and polysaccharide components were pursued by a solution NMR method and confirmed by compositional analysis of each fraction. Results: After hydrothermal pretreatment of rice straw, the NF concentrate of the supernatant of liquid fraction was hydrolyzed by hemicellulase and the resulting black precipitate was recovered. In this black precipitate, the intensity of NMR spectra related to lignin aromatic regions increased and those related to polysaccharides decreased, compared to rice straw, the solid fraction after hydrothermal pretreatment, and the NF concentrate. The lignin content of the black precipitate was 65.8 %. Lignin in the black precipitate included 52.9 % of the acid-insoluble lignin and 19.4 % of the soluble lignin in the NF concentrate of supernatant of liquid fraction. Conclusion: A precipitate with high lignin content was obtained from supernatants of the liquid fraction. These results suggested that precipitation of lignin was enhanced from concentrated mixtures of lignin and hemicellulosic polysaccharides by hydrolyzing the polysaccharides. Precipitation of lignin can contribute to lignin recovery from lignocellulosic biomass and, at the same time, allow more efficient ethanol production in the subsequent fermentation process.

    BIOMED CENTRAL LTD, Jun. 2015, BIOTECHNOLOGY FOR BIOFUELS, 8, 88, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Daisuke Sasaki, Hiroshi Teramura, Kentaro Inokuma, Tomohisa Hasunuma, Chiaki Ogino, Akihiko Kondo

    Mechanical milling and membrane separation were applied to simultaneous saccharification and co-fermentation from hydrothermally pretreated rice straw. Mechanical milling with minimized 4 cycles enabled 37.5 +/- 3.4 g L-1 and 45.3 +/- 4.4 g L-1 of ethanol production after 48 h by xylose-fermenting Saccharomyces cerevisiae from solid fractions (200 and 250 g L-1) of pretreated rice straw with 5 filter paper unit g-biomass(-1) cellulase (respectively, 77.3 +/- 7.1% and 74.7 +/- 7.3% of theoretical ethanol yield). Use of a membrane-based process including nanofiltration and ultrafiltration increased the sugar concentrations in the liquid fraction of pretreated rice straw and addition of this liquid fraction to 250 g L-1 solid fraction increased ethanol production to 52.0 +/- 0.4 g L-1 (73.8 +/- 0.6% of theoretical ethanol yield). Mechanical milling was effective in increasing enzymatic hydrolysis of the solid fraction and membrane separation steps increased the ethanol titer during co-fermentation, leading to a proposal for combining these processes for ethanol production from whole rice straw. (C) 2015 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Jun. 2015, BIORESOURCE TECHNOLOGY, 185, 263 - 268, English

    [Refereed]

    Scientific journal

  • Tomoyuki Hori, Shin Haruta, Daisuke Sasaki, Dai Hanajima, Yoshiyuki Ueno, Atsushi Ogata, Masaharu Ishii, Yasuo Igarashi

    Organic loading conditions are an important factor influencing reactor performances in methanogenic bioreactors. Yet the underlying microbiological basis of the process stability, deterioration, and recovery remains to be understood. Here, structural responses of the bacterial and archaeal populations to the change of organic loading conditions in a thermophilic anaerobic digester were investigated by process analyses and 16S rRNA gene-based molecular approaches. The biogas was produced stably without the accumulation of volatile fatty acids (VFAs) at low organic loading rates (OLRs) in the beginning of reactor operation. Increasing OLR in stages disrupted the stable reactor performance, and high OLR conditions continued the deteriorated performance with slight biogas production and high accumulation of VFAs. Thereafter, the gradual decrease of OLR resulted in the recovery from the deterioration, giving rise to the stable performance again. The stable performances before and after the high OLR conditions conducted were associated with compositionally similar but not identical methanogenic consortia. The bacterial and archaeal populations were synchronously changed at both the transient phases toward the deteriorated performance and in recovery process, during which the dynamic shift of aceticlastic and hydrogenotrophic methanogens including the recently identified Methanomassinicoccus might contribute to the maintenance of the methanogenic activity. The distinctive bacterial population with a high predominance of Methanobacterium formicicum as archaeal member was found for the deteriorated performance. The results in this study indicate the coordinated reorganization of the bacterial and archaeal populations in response to functional states induced by the change of organic loading conditions in the anaerobic digester. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Mar. 2015, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 119 (3), 337 - 344, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Yota Tsuge, Masahiko Morita, Akihiko Kondo

    Central metabolite profiles from glucose in microbial communities during methanogenic process were compared between a stable methanogenic reactor (MR) and a deteriorated reactor (DR). The concentrations of intracellular metabolites related to the Embden-Meyerhof and pentose phosphate pathways, with the exception of pyruvate, remained high in the MR, showing increased carbon flux in the glycolysis pathway during stable methanogenesis. Extracellular acetate temporarily accumulated in the MR, consistent with higher ATP level in the MR. Intracellular concentrations of the intermediates in the reductive branch of tricarboxylic acid cycle, malate, fumarate, and succinate were higher in the DR. Low NADH/NAD(+) ratio both in the MR and DR would suggest NADH consumption during acetate and lactate/succinate production in the MR and DR, respectively. Intracellular glutamate levels were higher in the MR, correlating with lower NADPH/NADP(+) ratio concentrations in the MR. These findings contribute to a better understanding of the metabolic state during stable methanogenesis. (C) 2014 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Nov. 2014, BIORESOURCE TECHNOLOGY, 172, 83 - 90, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Daisuke Sasaki, Tomohisa Hasunuma, Takatoshi Sakamoto, Yuri Sakihama, Chiaki Ogino, Akihiko Kondo

    Oligomeric sugars in the liquid fraction of hot water-pretreated rice straw are more amenable to membrane process than monomeric sugars, as lower pressure is required. Following membrane process was employed: nanofiltration (NF) concentration -> (dilution -> NF concentration) x 2 times -> enzymatic hydrolysis (EH) -> ultrafiltration (UF) permeation [Implication: NF for recovery of oligomeric sugars, dilution and NF for removal of low molecular weight fermentation inhibitors, UF for removal of high molecular weight fermentation inhibitors and recovery of monomeric sugars after EH]. This process provided the liquid fraction containing 111.4 g L-1 of sugars, corresponding to 681.0 mM as monomeric sugars, from the original liquid fraction (181.1 mM monomeric sugars). Concentrations of low molecular weight fermentation inhibitors, acetic and formic acids, were decreased to 24% and 48%, respectively. Xylose-fermenting recombinant Saccharomyces cerevisiae produced 34.5 +/- 2.2 g L-1 ethanol from the 0.8 times liquid fraction (76% of theoretical yield). (C) 2014 Published by Elsevier Ltd.

    ELSEVIER SCI LTD, Oct. 2014, BIORESOURCE TECHNOLOGY, 169, 380 - 386, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Daisuke Sasaki, Hiroshi Teramura, Satoshi Wakai, Hideo Kawaguchi, Takashi Sazuka, Chiaki Ogino, Akihiko Kondo

    The aim of this investigation was to attain high ethanol concentration by concentrating sweet sorghum juice using a two-step membrane separation process. Ultrafiltration permeation of the juice was used to remove residues, followed by nanofiltration concentration to increase the sugar concentration. The concentrated juice containing 180.0 g L-1 sucrose, 59.3 g L-1 glucose and 49.3 g L-1 fructose supplemented with nitrogen sources (10 and 20 g L-1 of yeast extract and polypeptone, respectively) was fermented by Saccharomyces cerevisiae BY4741 to produce 133.5 g L-1 of ethanol (87.6% of theoretical yield) after 48 h fermentation. Importantly, the addition of lower concentrations of exogenous nitrogen sources (3 and 6 g L-1 of yeast extract and polypeptone, respectively) or no exogenous nitrogen sources resulted in the production of 131.4 and 132.8 g L-1 of ethanol (84.8% and 86.0% of theoretical yield), respectively, after 48 h fermentation. (C) 2014 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Oct. 2014, BIORESOURCE TECHNOLOGY, 169, 821 - 825, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Yota Tsuge, Daisuke Sasaki, Akihiko Kondo

    Under conditions conductive to growth, Corynebacterium glutamicum showed higher lactate yield from glucose (1.62 +/- 0.04) in a bioelectrochemical reactor including 0.2 mM of anthraquinone 2,6-disulfonate with the electrode potential regulated at -0.6 V (vs. Ag/AgCl) than in a non-regulated environment (1.10 +/- 0.03), clarifying that low cathodic potential is beneficial for lactate production. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, May 2014, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 117 (5), 598 - 601, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Yuri Sakihama, Hiroshi Teramura, Ryosuke Yamada, Tomohisa Hasunuma, Chiaki Ogino, Akihiko Kondo

    Concentrating sugars using membrane separation, followed by ethanol fermentation by recombinant xylose-assimilating Saccharomyces cerevisiae, is an attractive technology. Three nanofiltration membranes (NTR-729HF, NTR-7250, and ESNA3) were effective in concentrating glucose, fructose, and sucrose from dilute molasses solution and no permeation of sucrose. The separation factors of acetate, formate, furfural, and 5-hydroxymethyl furfural, which were produced by dilute acid pretreatment of rice straw, over glucose after passage through these three membranes were 3.37-11.22, 4.71-20.27, 4.32-16.45, and 4.05-16.84, respectively, at pH 5.0, an applied pressure of 1.5 or 2.0 MPa, and 25 degrees C. The separation factors of these fermentation inhibitors over xylose were infinite, as there was no permeation of xylose. Ethanol production from approximately two-times concentrated liquid hydrolysate using recombinant S. cerevisiae was double (5.34-6.44 g L-1) that compared with fermentation of liquid hydrolysate before membrane separation (2.75 g L-1). (C) 2013 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Nov. 2013, BIORESOURCE TECHNOLOGY, 147, 84 - 88, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Daisuke Sasaki, Naoya Ohmura, Yasuo Igarashi

    The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to -0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8 +/- 9.1 mg-C center dot L-1 center dot day(-1)) and increased hydrogen production (12.6 A +/- 3.1 mg-H center dot L-1 center dot day(-1)) at pH(out) 6.2 A +/- 0.1, and the major intermediate was butyrate (24.9 A +/- 2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3 A +/- 17.9 mg-C center dot L-1 center dot day(-1)) and low hydrogen production (0.2 A +/- 0.0 mg-H center dot L-1 center dot day(-1)) at pH(out) 6.3 A +/- 0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3 A +/- 20.4 mg-C center dot L-1 center dot day(-1)) (pH(out), 7.2 A +/- 0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6 A +/- 1.7 mM) at pH(out) 5.0 A +/- 0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community.

    SPRINGER, Aug. 2013, APPLIED MICROBIOLOGY AND BIOTECHNOLOGY, 97 (15), 7005 - 7013, English

    [Refereed]

    Scientific journal

  • 電気化学システムを用いた模擬生ごみからの水素発酵の制御

    SASAKI KENGO, SASAKI DAISUKE, 森田 仁彦, 五十嵐 泰夫, KONDO AKIHIKO

    Mar. 2013, 水素エネルギーシステム, 38 (1), 33 - 37, Japanese

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Atsushi Watanabe, Masahiko Morita, Norio Matsumoto, Yasuo Igarashi, Naoya Ohmura

    A bioelectrochemical reactor (BER) containing carbon fiber fabric (CFF) (BER+CFF) enabled efficient methane fermentation from thickened sewage sludge. A cylindrical BER+CFF was proposed and scaled-up to a volume of 4.0-L. Thickened sewage sludge was treated using three types of methanogenic reactors. The working electrode potential in the BER+CFF was regulated at -0.8V (vs. Ag/AgCl). BER+CFF showed gas production of 3.57LL-1day-1 at a hydraulic retention time (HRT) of 4.0days however, non-BER+CFF showed a lower gas production rate (0.83LL-1day-1) at this HRT, suggesting positive effects of electrochemical regulation. A stirred tank reactor (without CFF) deteriorated at an HRT of 10days, suggesting positive effects of CFF. 16S rRNA gene analysis showed that the BER+CFF included 3 kinds of hydrogenotrophic methanogens and 1 aceticlastic methanogen. These results demonstrate the effectiveness of the BER+CFF for scale-up and flexibility of this technology. © 2012 Elsevier Ltd.

    Elsevier Ltd, 2013, Bioresource Technology, 129, 366 - 373, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Atsushi Watanabe, Masahiko Morita, Yasuo Igarashi, Naoya Ohmura

    A cylindrical bioelectrochemical reactor (BER) containing carbon fiber textiles (CFT BER + CFT) has characteristics of bioelectrochemical and packed-bed systems. In this study, utility of a cylindrical BER + CFT for degradation of a garbage slurry and recovery of biogas was investigated by applying 10% dog food slurry. The working electrode potential was electrochemically regulated at -0.8 V (vs. Ag/AgCl). Stable methane production of 9.37 L-CH4 · L-1 · day-1 and dichromate chemical oxygen demand (CODcr) removal of 62.5% were observed, even at a high organic loading rate (OLR) of 89.3 g-CODcr · L-1 · day-1. Given energy as methane (372.6 kJ · L-1 · day-1) was much higher than input electric energy to the working electrode (0.6 kJ · L-1 · day-1) at this OLR. Methanogens were highly retained in CFT by direct attachment to the cathodic working electrodes (52.3% ratio of methanogens to prokaryotes), compared with the suspended fraction (31.2%), probably contributing to the acceleration of organic material degradation and removal of organic acids. These results provide insight into the application of cylindrical BER + CFT in efficient methane production from garbage waste including a high percentage of solid fraction. © 2013 Sasaki et al. licensee Springer.

    Springer Verlag, 2013, AMB Express, 3 (17), 1 - 9, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Daisuke Sasaki, Norio Matsumoto, Naoya Ohmura, Yasuo Igarashi

    Bioelectrochemical systems (BESs) can control electric flow and resultant microbial activity. We designed a single chamber BES to investigate hydrogen production from artificial garbage slurry. A 3-electrode system was applied and the potential of the working electrode was regulated to -1.0 V (vs. Ag/AgCl). Thus, the potential on the counter electrode was 1.38 V (vs. Ag/AgCl). Hydrogen fermentation in the BES was initiated by methanogenic seed sludge. The BES achieved a hydrogen production rate of 2196 mL L-1 day(-1) at an organic loading rate of 58.7 g dichromate chemical oxygen demand L-1 day(-1). Acetate and butyrate were the main products, indicating that favorable hydrogen fermentation occurred in the system. Combination of high potential on the counter electrode and relatively low pH condition (5.5-6.4) was effective for constructing hydrogen fermentation even in single chamber system by inhibiting methanogenesis. However, it may be necessary to increase the space between the working and counter electrodes so as to decrease the electrical input. The single-chamber BES could be scaled-up for efficient hydrogen fermentation from garbage slurry. (C) 2012 Elsevier B.V. All rights reserved.

    ELSEVIER SCIENCE SA, Oct. 2012, BIOCHEMICAL ENGINEERING JOURNAL, 68, 104 - 108, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Masahiko Morita, Kengo Sasaki, Atsushi Watanabe, Naoya Ohmura

    Although the effects of syntrophic relationships between bacteria and methanogens have been reported in some environments, those on cellulose decomposition using cellulolytic bacteria from methanogenic reactors have not yet been examined. The effects of syntrophic co-culture on the decomposition of a cellulosic material were investigated in a co-culture of Clostridium clariflavum strain CL-1 and the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus strain Delta H and a single-culture of strain CL-1 under thermophilic conditions. In this study, strain CL-1 was newly isolated as a cellulolytic bacterium from a thermophilic methanogenic reactor used for degrading garbage slurry. The degradation efficiency and cell density of strain CL-1 were 2.9- and 2.7-fold higher in the co-culture than in the single-culture after 60 h of incubation, respectively. Acetate, lactate and ethanol were the primary products in both cultures, and the concentration of propionate was low. The content of acetate to total organic acids plus ethanol was 59.3% in the co-culture. However, the ratio decreased to 24.9% in the single-culture, although acetate was the primary product. Therefore, hydrogen scavenging by the hydrogenotrophic methanogen strain Delta H could shift the metabolic pathway to the acetate production pathway in the co-culture. Increases in the cell density and the consequent acceleration of cellulose degradation in the co-culture would be caused by increases in adenosine 5'-triphosphate (ATP) levels, as the acetate production pathway includes ATP generation. Syntrophic cellulose decomposition by the cellulolytic bacteria and hydrogenotrophic methanogens would be the dominant reaction in the thermophilic methanogenic reactor degrading cellulosic materials. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Oct. 2012, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 114 (4), 435 - 439, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Norio Matsumoto, Daisuke Sasaki, Shin-ichi Hirano, Naoya Ohmura, Yasuo Igarashi

    The aim of this study was to show the effectiveness of the membrane free bioelectrochemical system (BES) using three electrodes on inhibition of methanogenesis and construction of hydrogen fermentation from the artificial garbage slurry. The electrical redox-potential on the working electrode was adjusted to -1.0 V (vs. Ag/AgCl) that has positive effect on methanogenesis. The redox-potential on the counter electrode was measured to be 1.6 V. The pH in the effluents was 5.5-6.4. Hydrogen production rate at the cathode side was similar to that at the anode side and much higher than that calculated from current, and reached a maximum of 2445 +/- 815 (average standard deviation) mL L-1 d(-1) at an organic loading rate of 58.7 g dichromate chemical oxygen demand per L d(-1). Methane production was negligible throughout the experiment. Acetate and butyrate were the main products of the fermentation using a BES; these offered favorable conditions for hydrogen production. The bacterial community in the bioelectrochemical hydrogen fermentor differed from that in the methanogenic seed sludge and included hitherto unknown species. These results show that high redox-potential on the anodic electrode and acidic pH in the membrane free BES can be utilized for hydrogen fermentation from the artificial garbage slurry by avoiding methanogenesis. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Jul. 2012, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 114 (1), 64 - 69, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Kengo Sasaki, Masahiko Morita, Shin-ichi Hirano, Norio Matsumoto, Naoya Ohmura

    Bioelectrochemical systems can affect microbial metabolism by controlling the redox potential. We constructed bioelectrochemical cultures of the proteolytic bacterium, Coprothermobacter proteolyticus strain CT-1, both as a single-culture and as a co-culture with the hydrogenotrophic methanogen, Methanothermobacter thermautotrophicus strain Delta H, to investigate the influences of bioelectrochemical regulation on facultatively syntrophic proteolysis. The co-culture and single-culture were cultivated at 55 degrees C with an anaerobic medium containing casein as the carbon source. The working electrode potential of the bioelectrochemical system was controlled at -0.8 V (vs. Ag/AgCl) for bioelectrochemical cultures and was not controlled for non-bioelectrochemical cultures. The cell densities of hydrogenotrophic methanogen and methane production in the bioelectrochemical co-culture were 3.6 and 1.5 times higher than those in the non-bioelectrochemical co-culture after 7 days of cultivation, respectively. Contrastingly, the cell density of Coprothermobacter sp. in the bioelectrochemical co-culture was only 13 times higher than that in the non-bioelectrochemical co-culture. The protein decomposition rates were nearly proportional to the cell density of Coprothermobacter sp. in the all types of cultures. These results indicate that bioelectrochemical regulation, particularly, affected the carbon fixation of the hydrogenotrophic methanogen and that facultatively syntrophic proteolysis was accelerated as a result of hydrogen consumption by the methanogens growing well in bioelectrochemical co-cultures. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Jul. 2012, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 114 (1), 59 - 63, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Daisuke Sasaki, Jun Nagaoka, Norio Matsumoto, Naoya Ohmura, Hiraku Shinozaki

    Protein is a major component of organic solid wastes, and therefore, it is necessary to further elucidate thermophilic protein degradation process. The effects of hydrogenotrophic methanogens on protein degradation were investigated using the proteolytic bacterial strain CT-1 that was isolated from a methanogenic thermophilic (55 degrees C) packed-bed reactor degrading artificial garbage slurry. Strain CT-1 was closely related to Coprothermobacter proteolyticus, which is frequently found in methanogenic reactors degrading organic solid wastes. Strain CT-1 was cultivated in the absence or presence of Methanothermobacter thermautotrophicus by using 3 kinds of proteinaceous substrates. Degradation rates of casein, gelatin, and bovine serum albumin were higher in co-cultures than in monocultures. Strain CT-1 showed faster growth in co-cultures than in monocultures. M. thermautotrophicus comprised 53-6.0% of the total cells in co-culture. Increased production of ammonia and acetate was observed in co-cultures than in monocultures, suggesting that addition of M. thermautotrophicus increases the products of protein degradation. Hydrogen produced in the monocultures was converted to methane in co-cultures. These results suggest that thermophilic proteolytic bacteria find it favorable to syntrophically degrade protein in a methanogenic environment, and that it is important to retain hydrogen-scavenging methanogens within the reactor. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Nov. 2011, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 112 (5), 469 - 472, English

    [Refereed]

    Scientific journal

  • Tomoyuki Hori, Daisuke Sasaki, Shin Haruta, Toru Shigematsu, Yoshiyuki Ueno, Masaharu Ishii, Yasuo Lgarashi

    Syntrophic oxidation of acetate, so-called reversed reductive acetogenesis, is one of the most important degradation steps in anaerobic digesters. However, little is known about the genetic diversity of the micro-organisms involved. Here we investigated the activity and composition of potentially acetate-oxidizing syntrophs using a combinatorial approach of flux measurement and transcriptional profiling of the formyltetrahydrofolate synthetase (FTHFS) gene, an ecological biomarker for reductive acetogenesis. During the operation of a thermophilic anaerobic digester, volatile fatty acids were mostly depleted, suggesting a high turnover rate for dissolved H(2), and hydrogenotrophic methanogens were the dominant archaeal members. Batch cultivation of the digester microbiota with (13)C-labelled acetate indicated that syntrophic oxidation accounted for 13.1-21.3% of methane production from acetate. FTHFS genes were transcribed in the absence of carbon monoxide, methoxylated compounds and inorganic electron acceptors other than CO(2), which is implicated in the activity of reversed reductive acetogenesis; however, expression itself does not distinguish whether biosynthesis or biodegradation is functioning. The mRNA-and DNA-based terminal RFLP and clone library analyses indicated that, out of nine FTHFS phylotypes detected, the FTHFS genes from the novel phylotypes I-IV in addition to the known syntroph Thermacetogenium phaeum (i.e. phylotype V) were specifically expressed. These transcripts arose from phylogenetically presumed homoacetogens. The results of this study demonstrate that hitherto unidentified phylotypes of homoacetogens are responsible for syntrophic acetate oxidation in an anaerobic digester.

    SOC GENERAL MICROBIOLOGY, Jul. 2011, MICROBIOLOGY-SGM, 157, 1980 - 1989, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Daisuke Sasaki, Shin-ichi Hirano, Norio Matsumoto, Atsushi Watanabe, Naoya Ohmura, Yasuo Igarashi

    A packed-bed system includes supporting materials to retain microorganisms and a bioelectrochemical system influences the microbial metabolism. In our study, carbon fiber textiles (CFT) as a supporting material was attached onto a carbon working electrode in a bioelectrochemical reactor (BER) that degrades garbage slurry to methane, in order to investigate the effect of combining electrochemical regulation and packing CFT. The potential on the working electrode in the BER containing CFT was set to -1.0 V or -0.8 V (vs. Ag/AgCl). BERs containing CFT exhibited higher methane production, elimination of dichromate chemical oxygen demand, and the ratio of methanogens in the suspended fraction than reactors containing CFT without electrochemical regulation at an organic loading rate (OLR) of 27.8 gCODcr/L/day. In addition, BERs containing CFT exhibited higher reactor performances than BERs without CFT at this OLR. Our results revealed that the new design that combined electrochemical regulation and packing CFT was effective. (C) 2011 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, Jul. 2011, BIORESOURCE TECHNOLOGY, 102 (13), 6837 - 6842, English

    [Refereed]

    Scientific journal

  • Daisuke Sasaki, Tomoyuki Hori, Shin Haruta, Yoshiyuki Ueno, Masaharu Ishii, Yasuo Igarashi

    The methanogenic pathway and microbial community in a thermophilic anaerobic digestion process of organic solid waste were investigated in a continuous-flow stirred-tank reactor using artificial garbage slurry as a feedstock. The decomposition pathway of acetate, a significant precursor of CH4 and a key intermediate metabolite in the anaerobic digestion process, was analyzed by using stable isotopes. A tracer experiment using C-13-labeled acetate revealed that approximately 80% of the acetate was decomposed via a non-aceticlastic oxidative pathway, whereas the remainder was converted to methane via an aceticlastic pathway. Archaeal 16S rRNA analyses demonstrated that the hydrogenotrophic methanogens Methanoculleus spp. accounted for >90% of detected methanogens, and the aceticlastic methanogens Methanosarcina spp. were the minor constituents. The clone library targeting bacterial 16S rRNA indicated the predominance of the novel Thermotogales bacterium (relative abundance: similar to 53%), which is related to anaerobic acetate oxidizer Thermotoga lettingae TMO, although the sequence similarity was low. Uncultured bacteria that phylogenetically belong to municipal solid waste cluster I were also predominant in the microflora (similar to 30%). These results imply that the microbial community in the thermophilic degrading process of organic solid waste consists exclusively of unidentified bacteria, which efficiently remove acetate through a non-aceticlastic oxidative pathway. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Jan. 2011, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 111 (1), 41 - 46, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Daisuke Sasaki, Shin-ichi Hirano, Norio Matsumoto, Naoya Ohmura, Yasuo Igarashi

    Methane fermentation was successfully carried out in bioelectrochemical reactors without membranes under a working potential of -0.6 or -0.8 V (vs. Ag/AgCl) and neutral pH conditions. The hydrogenotrophic methanogens that dominated on the anodic and cathodic electrodes differed from those found on the electrodes in the control reactors without electrochemical reactions. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.

    SOC BIOSCIENCE BIOENGINEERING JAPAN, Jan. 2011, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 111 (1), 47 - 49, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Shin-ichi Hirano, Masahiko Morita, Daisuke Sasaki, Norio Matsumoto, Naoya Ohmura, Yasuo Igarashi

    Bioelectrochemical reactors (BERs) with a cathodic working potential of -0.6 or -0.8 V more efficiently degraded cellulosic material, i.e., filter paper (57.4-74.1% in 3 days and 95.9-96.3% in 7 days) than did control reactors without giving exogenous potential (15.4% in 3 days and 64.2% in 7 days). At the same time, resultant conversions to methane and carbon dioxide in cathodic working chamber of BERs by application of electrochemical reduction in 3 days of operation were larger than control reactors. However, cumulative methane production in cathodic BERs was similar to those in control reactors after 7 days of operation. Microscopic observation and 16S rRNA gene analysis showed that microbial growth in the entire consortium was higher after 2 days of operation of cathodic BERs as compared with the control reactors. In addition, the number of methanogenic 16S rRNA gene copies in cathodic BERs was higher than in control reactors. Moreover, archaeal community structures constructed in cathodic BERs consisted of hydrogenotrophic methanogen-related organisms and differed from those in control reactors after 2 days of operation. Specifically, the amount of Methanothermobacter species in cathodic BERs was higher within archaeal communities than in those control reactors after 2 days of operation. Electrochemical reduction may be effective for accelerating microbial growth in the start-up period and thereby increasing microbial treatment of cellulosic waste and methane production.

    SPRINGER, Jan. 2011, APPLIED MICROBIOLOGY AND BIOTECHNOLOGY, 89 (2), 449 - 455, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Masahiko Morita, Shin-ichi Hirano, Daisuke Sasaki, Naoya Ohmura, Yasuo Igarashi

    We have reported for the first time that agricultural and cellulosic waste, i.e., rice straw was directly applied to methanogenic bioreactors containing carbon fiber textiles (CFT) as supporting material. Addition of CFT to the methanogenic bioreactors enhanced the conversion of dichromate chemical oxygen demand of the substrate to methane (41%) to a greater extent than bioreactors without CFT (9%). In addition, removal of rice straw as a suspended solid was increased from 31% (in bioreactors without CFT) to 57% (in those with CFT). Methanogenic 16S rRNA gene analysis showed that the abundance of acetoclastic methanogen, genus Methanosarcina, was about 11 times higher in bioreactors with CFT (suspended fraction plus retained fraction to CFT) than in bioreactors without CFT (suspended fraction), resulting in lower concentration of acetate in bioreactors with CFT (0.4 mM) than in those without CFT (29.7 mM). On the other hand, the abundance of hydrogenotrophic methanogen, genus Methanobacterium, in bioreactors with CFT was similar to those without CFT. Bacterial communities in bioreactors with CFT were different from those in bioreactors without CFT. Our results indicated that specific microbial community and cooperative relationships between microorganisms in reactors containing CFT facilitated efficient decomposition of rice straw and its conversion to methane.

    SPRINGER, Jul. 2010, APPLIED MICROBIOLOGY AND BIOTECHNOLOGY, 87 (4), 1579 - 1586, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Masahiko Morita, Shin-ichi Hirano, Norio Matsumoto, Naoya Ohmura, Yasuo Igarashi

    Adding a supporting material to a methanogenic bioreactor treating garbage slurry can improve efficiency of methane production. However, little is known on how characteristics (e.g., porosity and hydrophobicity) of the supporting material affect the bioreactor degrading garbage slurry. We describe the reactor performances and microbial communities in bioreactors containing hydrophilic or hydrophobic sheets, or fibrous hydrophilic or hydrophobic sponges. The porosity affected the efficiency of methane production and solid waste removal more than the hydrophilic or hydrophobic nature of the supporting material. When the terminal restriction fragment length polymorphism technique was used at a lower organic loading rate (OLR), microbial diversities in the suspended fraction were retained on the hydrophobic, but not the hydrophilic, sheets. Moreover, real-time quantitative polymerase chain reaction (PCR) performed at a higher OLR revealed that the excellent performance of reactors containing fibrous sponges with high porosity (98%) was supported by a clear increase in the numbers of methanogens on these sponges, resulting in larger total numbers of methanogens in the reactors. In addition, the bacterial communities in fractions retained on both the hydrophobic and hydrophilic fibrous sponges differed from those in the suspended fraction, thus increasing bacterial diversity in the reactor. Thus, higher porosity of the supporting material improves the bioreactor performance by increasing the amount of methanogens and bacterial diversity; surface hydrophobicity contributes to maintaining the suspended microbial community.

    SPRINGER, May 2010, APPLIED MICROBIOLOGY AND BIOTECHNOLOGY, 86 (5), 1573 - 1583, English

    [Refereed]

    Scientific journal

  • Kengo Sasaki, Daisuke Sasaki, Masahiko Morita, Shin-ichi Hirano, Norio Matsumoto, Naoya Ohmura, Yasuo Igarashi

    Methanogenic bioreactors, which are packed with supporting material, have attracted attention as an efficient means of degrading garbage. We aimed to increase bioreactor performance by using an electrochemical system to regulate the electrical potential on supporting material. At an organic loading rate of 26.9 g dichromate chemical oxygen demand (CODcr)/L/day, reactors with a potential of -0.6 or -0.8 V, generated by a cathodic electrochemical reaction, showed greater removal of CODcr and methanogenesis than reactors with a potential of 0.0 or -0.3 V, generated by anodic reaction, or control reactors without electrochemical regulation. 16S rRNA gene analysis revealed that the same methanogens were present in all our reactors, but quantitative real-time polymerase chain reaction showed that higher prokaryotic and methanogenic copy numbers were present on cathodic electrodes than on anodic or control electrodes. These results indicate that cathodic electrochemical regulation can support methane fermentation from garbage. (C) 2009 Elsevier Ltd. All rights reserved.

    ELSEVIER SCI LTD, May 2010, BIORESOURCE TECHNOLOGY, 101 (10), 3415 - 3422, English

    [Refereed]

    Scientific journal

  • Y. Ueno, D. Sasaki, H. Fukui, S. Haruta, M. Ishii, Y. Igarashi

    Aims: Changes in fermentation pattern during the treatment of organic wastes containing solid materials by thermophilic anaerobic microflora were investigated with respect to product formation and bacterial community structure during hydrogen production. Methods and Results: Anaerobic microflora enriched from sludge compost was cultivated using artificial garbage slurry in a continuous flow-stirred tank reactor. Product formation varied depending on pH and hydraulic retention time (HRT) applied. Community analysis by terminal restriction fragment length polymorphism and clone library analysis of polymerase chain reaction-amplified bacterial 16S rDNA indicated that difference in the fermentative product distribution could be caused by different populations of micro-organisms in the microflora. Conclusion: Hydrogen fermentation with acetate/butyrate formation was optimized at < 1.0 d HRT at pH 5.0 and 6.0. Thermoanaerobacterium thermosaccharolyticum was the dominant hydrogen-producing micro-organism. Conversely, unidentified organisms became dominant after 4.0 d HRT at pH 7.0 and 8.0, where relatively high-solubilization efficiency of solid materials was observed with no production of hydrogen. Significance and Impact of the Study: This is the first report describing product formation in the fermentation of solid organic wastes by a mixed population of micro-organisms. Various fermentation patterns including hydrogen fermentation were characterized and evaluated from engineering and microbial aspects.

    BLACKWELL PUBLISHING, Aug. 2006, JOURNAL OF APPLIED MICROBIOLOGY, 101 (2), 331 - 343, English

    [Refereed]

    Scientific journal

  • Y Okuda, D Sasaki, S Nogami, Y Kaneko, Y Ohya, Y Anraku

    VDE is a homing endonuclease gene originally discovered as an intervening element in VMA1s of Saccharomyces cerevisiae. There have been two independent subfamilies of VDE, one from S. cerevisiae strain X2180-1A and the other from Saccharomyces sp. DH1-1A in the host VMA1 gene, and they share the identity of 96.3%. In order to search the occurrence, intra/interspecies transfer and molecular degeneration of VDE, complete sequences of VMA1 in 10 strains of S. cerevisiae, eight species of saccharomycete yeasts, Candida glabrata and Kluyveromyces lactis were determined. We found that six of 10 S. cerevisiae strains contain VDEs 99.7-100% identical to that of the strain X2180-1A, one has no VDE, whereas the other three harbour VDEs 100% identical to that of the strain DH1-1A. S. carlsbergensis has two VMA1s, one being 99.8% identical to that of the strain X2180-1A with VDE 100% identical to that of the strain DH1-1A and the other containing the same VMA1 in S. pastorianus with no VDE. This and other evidence indicates that intra/interspecies transmissions of VDEs have occurred among saccharomycete yeasts. Phylogenetic analyses of VMA1 and VDE suggest that the S. cerevisiae VDEs had branched earlier than other VDEs from an ancestral VDE and had invaded into the host loci as relatively late events. The two VDEs seemed to degenerate in individual host loci, retaining their splicing capacity intact. The degeneration of the endonuclease domains was distinct and, if compared, its apparent rate was much faster than that of the protein-splicing domains. The VMA1 gene sequences determined in this study have been deposited in the GenBank data library under the Accession Nos shown in Table 1. Copyright (C) 2003 John Wiley Sons, Ltd.

    JOHN WILEY & SONS LTD, May 2003, YEAST, 20 (7), 563 - 573, English

    [Refereed]

    Scientific journal

  • Jyumpei Kobayashi, Daisuke Sasaki, Kiyotaka Y Hara, Tomohisa Hasunuma, Akihiko Kondo

    BACKGROUND: Glutathione is a valuable tri-peptide that is industrially produced by fermentation using the yeast Saccharomyces cerevisiae, and is widely used in the pharmaceutical, food, and cosmetic industries. It has been reported that addition of L-serine (L-Ser) is effective at increasing the intracellular glutathione content because L-Ser is the common precursor of L-cysteine (L-Cys) and glycine (Gly) which are substrates for glutathione biosynthesis. Therefore, we tried to enhance the L-Ser biosynthetic pathway in S. cerevisiae for improved glutathione production. RESULTS: The volumetric glutathione production of recombinant strains individually overexpressing SER2, SER1, SER3, and SER33 involved in L-Ser biosynthesis at 48 h cultivation was increased 1.3, 1.4, 1.9, and 1.9-fold, respectively, compared with that of the host GCI strain, which overexpresses genes involved in glutathione biosynthesis. We further examined simultaneous overexpression of SHM2 and/or CYS4 genes involved in Gly and L-Cys biosynthesis, respectively, using recombinant GCI strain overexpressing SER3 and SER33 as hosts. As a result, GCI overexpressing SER3, SHM2, and CYS4 showed the highest volumetric glutathione production (64.0 ± 4.9 mg/L) at 48 h cultivation, and this value is about 2.5-fold higher than that of the control strain. CONCLUSIONS: This study first revealed that engineering of L-Ser and Gly biosynthetic pathway are useful strategies for fermentative glutathione production by S. cerevisiase.

    06 Aug. 2022, Microbial cell factories, 21 (1), 153 - 153, English, International magazine

    Scientific journal

MISC

  • 電気化学的前処理/通電式担体充填による2段発酵を廃水・廃棄物処理へ適用

    佐々木建吾, 佐々木大介, 近藤昭彦

    May 2021, 化学と生物, 59 (12), 247 - 253, Japanese

  • ヒト腸内細菌叢モデルによるプレバイオティクスの評価

    SASAKI DAISUKE, SASAKI KENGO

    Aug. 2019, アグリバイオ, 3 (9), 53 - 58, Japanese

    Introduction scientific journal

  • 日本人潰瘍性大腸炎患者の腸内細菌叢における2種の酪酸産生遺伝子の定量

    篠原 涼平, 佐々木 建吾, 井上 潤, 星 奈美子, 福田 伊津子, 佐々木 大介, 近藤 昭彦, 大澤 朗

    (公財)日本ビフィズス菌センター, Apr. 2019, 腸内細菌学雑誌, 33 (2), 105 - 105, Japanese

  • in viro培養システムによる食物繊維のヒト腸管細菌叢への影響評価

    SASAKI DAISUKE, SASAKI KENGO, KONDO AKIHIKO, OSAWA RO

    Dec. 2018, ルミナコイド研究(日本食物繊維学会誌), 22 (2), 63 - 74, Japanese

    Introduction scientific journal

  • 培養系ヒト腸内細菌叢モデルKUHIMMを利用した食物繊維の影響評価

    IKUTA NAOKO, 篠原 涼平, SASAKI DAISUKE, SASAKI KENGO

    May 2018, New Food Industry, 60 (5), 37 - 43, Japanese

    Introduction scientific journal

  • 微粉砕・メタン発酵・高度膜分離による稲わらの利用

    佐々木建吾, 白井智量, 柘植陽太, 佐々木大介, 菊地淳, 近藤昭彦

    05 Mar. 2017, 日本農芸化学会大会講演要旨集(Web), 2017, ROMBUNNO.4J28a09 (WEB ONLY), Japanese

  • 1P-219 Membrane process increased ethanol production from pretreated rice straw.

    Sasaki Kengo, Tsuge Yota, Sasaki Daisuke, Ogino Chiaki, Kondo Akihiko

    日本生物工学会, 2014, 日本生物工学会大会講演要旨集, 66, 72 - 72, Japanese

  • Daisuke Sasaki, Masahiko Morita, Kengo Sasaki, Atsushi Watanabe, Naoya Ohmura

    Bioelectrochemical (-0.8 V, -0.3 V, and +0.6V vs. Ag/AgCl) and non-bioelectrochemical co-cultures of a hydrogenotrophic methanogen and a cellulolytic bacterium were conducted. Unlike non-bioelectrochemical co-cultures, a cathodic reaction (-0.8 V) increased the growth of the hydrogenotrophic methanogen and the cellulolytic bacterium, by 6.0- and 2.2-fold respectively, and increased cellulose degradation. In contrast, anodic reactions (-0.3 V, +0.6 V) influenced them negatively.

    2013, Bioscience, Biotechnology and Biochemistry, 77 (5), 1096 - 1099, English

    [Refereed]

    Report scientific journal

  • 1P-209 Characterization of anaerobic digestion by metabolomic analysis derived from microbial community

    SASAKI Daisuke, SASAKI Kengo, NAKANISHI Shuji, HASHIMOTO Kazuhito, KONDO Akihiko

    日本生物工学会, 2013, 日本生物工学会大会講演要旨集, 65, 70 - 70, Japanese

  • S19-2 Control of methanogenic microbial community using bioelectrochemical system(Session 19 Engineering tecnology in microbiology,Symposium session)

    Sasaki Kengo, Sasaki Daisuke, Morita Masahiko, Igarashi Yasuo

    日本微生物生態学会, 2012, 日本微生物生態学会講演要旨集, (28), 127 - 127, English

  • 3P-144 Comparison of microbial metabolites between methane fermentation and acid fermentation

    Sasaki Daisuke, Sasaki Kengo, Tsuge Yota, Nakanishi Shuji, Kondo Akihiko

    日本生物工学会, 2014, 日本生物工学会大会講演要旨集, 66, 230 - 230, Japanese

  • 2Ha11 Effect of facultatively syntrophic proteolysis by bioelectrochemical regulation

    SASAKI Daisuke, SASAKI Kengo, MORITA Masahiko, HIRANO Shin-ichi, MATSUMOTO Norio, OHMURA Naoya

    日本生物工学会, 2012, 日本生物工学会大会講演要旨集, 64, 71 - 71, Japanese

  • 2Ca03 Analysis of bioelectrochemical packed-bed methanogenic reactor degrading sewage sludge

    Sasaki Daisuke, Sasaki Kengo, Watanabe Atsushi, Morita Masahiko, Hirano Shin-ichi, Matsumoto Norio, Uemoto Hiroaki, Ohmura Naoya, Igarashi Yasuo

    日本生物工学会, 2011, 日本生物工学会大会講演要旨集, 63, 125 - 125, Japanese

  • P-79 Changes of gas production and microbial community by addition of ferric iron oxide or manganese oxide on the acetate degradation in thermophilic methane fermentation(Poster Session)

    YAMADA CHIHAYA, UENO YOSHIYUKI, SASAKI DAISUKE, SASAKI KENGO, ISHII MASAHARU, IGARASHI YASUO

    日本微生物生態学会, 2010, 日本微生物生態学会講演要旨集, (26), 134 - 134, English

  • 2Hp01 Effect of surface characteristics of support materials on packed-bed reactors

    SASAKI Kengo, MORITA Masahiko, HIRANO Shinichi, MATSUMOTO Norio, UEMOTO Hiroaki, OHMURA Naoya, SASAKI Daisuke, HARUTA Shin, IGARASHI Yasuo

    日本生物工学会, 2008, 日本生物工学会大会講演要旨集, 20, 198 - 198, Japanese

Books etc

  • Genetic engineering of microorganisms for high glutathione production, Glutathione: Biosynthesis, Functions and Biological Implications

    KOBAYASHI Jyumpei, SASAKI Daisuke, HARA Y. Kiyotaka, KONDO Akihiko

    Joint work, Nova Science Publishers, Feb. 2019, English

    Scholarly book

Presentations

  • 微生物燃料電池:アノード電極上のバイオマス量および細胞内グルタミン酸濃度と電流生成の相関

    SASAKI DAISUKE, SASAKI KENGO, TSUGE YOTA, KONDO AKIHIKO

    第71回日本生物工学会大会, Sep. 2019, Japanese, 岡山大学, Domestic conference

    Oral presentation

  • 解糖系とペントースリン酸経路への代謝フラックスの分岐比が細胞内代謝プロファイルに及ぼす影響

    村井 克輝, SASAKI DAISUKE, 白井 智量, 内倉 寛斗, SASAKI KENGO, 仁宮 一章, 高橋 憲司, KONDO AKIHIKO, 柘植 陽太

    第71回日本生物工学会大会, Sep. 2019, Japanese, 岡山大学, Domestic conference

    Oral presentation

  • バイオ電気化学的システムによる複合微生物系の制御

    SASAKI KENGO, SASAKI DAISUKE, 森田 仁彦, TSUGE YOTA, KONDO AKIHIKO

    第71回日本生物工学会大会, Sep. 2019, Japanese, 岡山大学, Domestic conference

    Oral presentation

  • 冠動脈疾患患者大腸フローラモデルによる候補投与物の調査

    SASAKI KENGO, 吉田 尚史, SASAKI DAISUKE, OSAWA RO, YAMASHITA TOMOYA, 近藤 昭彦

    日本農芸化学会2019年度大会, Mar. 2019, Japanese, 東京農業大学 世田谷キャンパス, Domestic conference

    Poster presentation

  • E2a5ソルガムバガスの酵素糖化効率支配因子の探索

    川口秀夫, 佐々木大介, 福本妙子, 森田健太, 竹中武蔵, 冨田康平, 佐塚隆志, 松本拓也, 西野孝, 近藤昭彦

    日本農芸化学会 関西・中部支部 2019年度合同神戸大会, 22 Sep. 2018, Japanese, Domestic conference

    Oral presentation

  • 腸内細菌Bacteroides thetaiotaomicronによる食物繊維の資化性に関する研究

    篠原 涼平, 古根 隆広, 生田 直子, 佐々木 大介, 佐々木 建吾, 福田 伊津子, 大澤 朗, 坂本 憲広

    第70回日本生物工学会大会, Sep. 2018, Japanese, 関西大学 千里山キャンパス, Domestic conference

    Poster presentation

  • 組換え出芽酵母Saccharomyces cerevisiaeによるキシロースからのグルタチオン生産

    小林 淳平, 佐々木 大介, 番場 崇弘, 蓮沼 誠久, 近藤 昭彦

    第70回日本生物工学会大会, Sep. 2018, Japanese, 関西大学 千里山キャンパス, Domestic conference

    Poster presentation

  • in vitro培養系ヒト腸内細菌叢モデル(KUHIMM) を用いた難消化性食物繊維の影響評価

    SASAKI DAISUKE, SASAKI KENGO, IKUTA NAOKO, FUKUDA ITSUKO, KONDO AKIHIKO, OSAWA RO

    第70回日本生物工学会大会, Sep. 2018, Japanese, 関西大学 千里山キャンパス, Domestic conference

    Poster presentation

  • In vitro培養系ヒト腸内細菌叢モデルによる潰瘍性大腸炎患者の代謝プロファイル異常の検出

    SASAKI KENGO, INOUE JUN, HOSHI NAMIKO, SASAKI DAISUKE, FUKUDA ITSUKO, KONDO AKIHIKO, OSAWA RO

    第70回日本生物工学会大会, Sep. 2018, Japanese, 関西大学 千里山キャンパス, Domestic conference

    Poster presentation

  • In vitro潰瘍性大腸炎患者大腸フローラモデルの構築

    Kengo Sasaki, 井上 潤, 星 奈美子, Daisuke Sasaki, Akihiko Kondo, Ro Osawa

    日本農芸化学会2018年度大会, Mar. 2018, Japanese, 日本農芸化学会, 名古屋市, Domestic conference

    Poster presentation

  • 異なる pHで運転した微生物燃料電池:アノード電極上の微生物群集に由来する細胞内代謝物の 比較

    Daisuke Sasaki, Kengo Sasaki, 柘植 陽太, Akihiko Kondo

    第69回日本生物工学会大会, Sep. 2017, Japanese, 日本生物工学会, 東京都新宿区, Domestic conference

    Oral presentation

  • Effects of indigestible dietary fibers on human intestinal microbiota simulated in a single-batch fermentation system

    SASAKI DAISUKE, SASAKI KENGO, IKUTA NAOKO, KONDO AKIHIKO, OSAWA RO

    第21回腸内細菌学会, Jun. 2017, English, 第21回腸内細菌学会, 神戸市, Domestic conference

    Oral presentation

  • 変異チオール酸化酵素による酵母の酸化型グルタチオン 生産

    小林淳平, Sasaki Daisuke, 原 清敬, Hasunuma Tomohisa, KONDO Akihiko

    日本農芸化学2017年度大会, Mar. 2017, Japanese, 日本農芸化学会, 京都市, Domestic conference

    Oral presentation

  • 微粉砕・メタン発酵・高度膜分離による稲わらの利用

    Sasaki Kengo, 白井智量, Tsuge Youta, Sasaki Daisuke, 菊地 淳, KONDO Akihiko

    日本農芸化学2017年度大会, Mar. 2017, Japanese, 日本農芸化学会, 京都市, Domestic conference

    Oral presentation

  • KUHIMM による難消化性食物繊維の腸内細菌叢への影響評価

    Sasaki Daisuke, Sasaki Kengo, 生田 直子, KONDO Akihiko, 大澤 朗

    第2回デザイン生命工学研究会大会, Mar. 2017, Japanese, デザイン生命工学研究会, 神戸市, Domestic conference

    Oral presentation

  • ヒト腸管モデルによるタウリンの腸内細菌叢内での動態の検証

    Sasaki Kengo, Sasaki Daisuke, KONDO Akihiko, 大澤朗

    第69回日本細菌学会関西支部総会・学術講演会, Nov. 2016, Japanese, 日本細菌学会関西支部, 大阪市, Domestic conference

    Oral presentation

  • 微生物燃料電池アノード電極上の微生物群集細胞内代謝解析

    Sasaki Daisuke, Sasaki Kengo, Tsuge Youta, KONDO Akihiko

    第68回日本生物工学会大会, Sep. 2016, Japanese, 日本生物工学会, 富山市, Domestic conference

    Oral presentation

  • pH非調整型の培養系ヒト腸管モデルの確立

    Sasaki Kengo, Sasaki Daisuke, KONDO Akihiko, 大澤 朗

    第68回日本生物工学会大会, Sep. 2016, Japanese, 日本生物工学会, 富山市, Domestic conference

    Oral presentation

  • 膜濃縮したソルガム搾汁液からのエタノール発酵

    SASAKI KENGO, TSUGE YOTA, SASAKI DAISUKE, 寺村 浩, KAWAGUCHI HIDEO, OGINO CHIAKI, 春日 重光, 佐塚 隆志, KONDO AKIHIKO

    日本農芸化学会2015年度大会, Mar. 2015, Japanese, 日本農芸化学会, 岡山市, Domestic conference

    Oral presentation

  • 稲わら前処理液の膜プロセスによるエタノール発酵高効率化

    SASAKI KENGO, TSUGE YOTA, SASAKI DAISUKE, OGINO CHIAKI, KONDO AKIHIKO

    第66回日本生物工学会大会, Sep. 2014, Japanese, 日本生物工学会, 札幌市, Domestic conference

    Poster presentation

  • メタン発酵・酸発酵環境における微生物内代謝物の比較

    SASAKI DAISUKE, SASAKI KENGO, TSUGE YOTA, 中西 周次, KONDO AKIHIKO

    第66回日本生物工学会大会, Sep. 2014, Japanese, 日本生物工学会, 札幌市, Domestic conference

    Poster presentation

  • Corynebacterium glutamicum増殖時の電気培養下での乳酸生成

    SASAKI KENGO, TSUGE YOTA, SASAKI DAISUKE, KONDO AKIHIKO

    日本農芸化学会2014年度大会, Mar. 2014, Japanese, 日本農芸化学会, 川崎市, Domestic conference

    Oral presentation

  • 微生物群集を対象とした代謝解析による嫌気消化の特徴付け

    SASAKI DAISUKE, SASAKI KENGO, 中西 周次, 橋本 和仁, KONDO AKIHIKO

    第65回日本生物工学会大会, Sep. 2013, Japanese, 日本生物工学会, 広島市, Domestic conference

    Poster presentation

  • タンパク質共生分解における電気化学的制御の影響

    SASAKI DAISUKE, Sasaki Kengo, Morita Masahiko, Hirano Shin-ichi, Matsumoto Norio, Ohmura Naoya

    日本生物工学会, Oct. 2012, Japanese, 神戸国際会議場, 【目的】我々は電気化学システムを用いた有機性廃棄物からのメタン発酵を評価し、報告してきた。これらの結果から、発酵液を還元電位に制御することによるメタン生成の安定化が明らかとなったが、その効果の由来は定かではなかった。そこで高温メタン発酵槽から分離したタンパク質分解菌と水素資化性メタン菌を用いて通電共培養を行い、通電の影響について評価し、その効果の明確化を試みた。 【方法】250mLの通電培養槽に対して、3電極方式によって-0.8V(vs. Ag/AgCl)に通電しながらスターラーで撹拌を行い、カゼインを炭素源とする培地を用いて55℃で嫌気培養を行った。通電の有り無しで共培養を行うと共に、タンパク質分解菌のみの単菌培養を対照区として計4通りの条件で培養を行い、各種パラメーターを経時的に解析した。 【結果】通電ありの共培養において菌体密度、タンパク質分解, Domestic conference

    Oral presentation

  • 大麦若葉エキスがヒト大腸細菌叢に与える効果についての検討

    佐々木 建吾, 佐々木 大介, 門脇 靖司, 青塚 康幸, 近藤 昭彦

    日本農芸化学会2020年度大会

Research Projects