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Du Y, Zou W, Zhang K, Ye G, Yang J. Advances and Applications of Clostridium Co-culture Systems in Biotechnology. Front Microbiol 2020; 11:560223. [PMID: 33312166 PMCID: PMC7701477 DOI: 10.3389/fmicb.2020.560223] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 10/20/2020] [Indexed: 01/09/2023] Open
Abstract
Clostridium spp. are important microorganisms that can degrade complex biomasses such as lignocellulose, which is a widespread and renewable natural resource. Co-culturing Clostridium spp. and other microorganisms is considered to be a promising strategy for utilizing renewable feed stocks and has been widely used in biotechnology to produce bio-fuels and bio-solvents. In this review, we summarize recent progress on the Clostridium co-culture system, including system unique advantages, composition, products, and interaction mechanisms. In addition, biochemical regulation and genetic modifications used to improve the Clostridium co-culture system are also summarized. Finally, future prospects for Clostridium co-culture systems are discussed in light of recent progress, challenges, and trends.
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Affiliation(s)
- Yuanfen Du
- College of Bioengineering, Sichuan University of Science and Engineering, Yibin, China.,Research Laboratory of Baijiu Resource Microorgannisms and Big Data, Sichuan University of Science and Engineering, Yibin, China
| | - Wei Zou
- College of Bioengineering, Sichuan University of Science and Engineering, Yibin, China.,Research Laboratory of Baijiu Resource Microorgannisms and Big Data, Sichuan University of Science and Engineering, Yibin, China
| | - Kaizheng Zhang
- College of Bioengineering, Sichuan University of Science and Engineering, Yibin, China
| | - Guangbin Ye
- College of Bioengineering, Sichuan University of Science and Engineering, Yibin, China
| | - Jiangang Yang
- College of Bioengineering, Sichuan University of Science and Engineering, Yibin, China
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2
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Coban HB. Organic acids as antimicrobial food agents: applications and microbial productions. Bioprocess Biosyst Eng 2019; 43:569-591. [PMID: 31758240 DOI: 10.1007/s00449-019-02256-w] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 11/11/2019] [Indexed: 12/30/2022]
Abstract
Food safety is a global health and socioeconomic concern since many people still suffer from various acute and life-long diseases, which are caused by consumption of unsafe food. Therefore, ensuring safety of the food is one of the most essential issues in the food industry, which needs to be considered during not only food composition formulation but also handling and storage. For safety purpose, various chemical preservatives have been used so far in the foods. Recently, there has been renewed interest in replacing chemically originated food safety compounds with natural ones in the industry, which can also serve as antimicrobial agents. Among these natural compounds, organic acids possess the major portion. Therefore, in this paper, it is aimed to review and compile the applications, effectiveness, and microbial productions of various widely used organic acids as antimicrobial agents in the food industry.
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Affiliation(s)
- Hasan Bugra Coban
- Izmir International Biomedicine and Genome Institute, Dokuz Eylul University Health Campus, Balcova, 35340, Izmir, Turkey.
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3
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Eng A, Borenstein E. Microbial community design: methods, applications, and opportunities. Curr Opin Biotechnol 2019; 58:117-128. [PMID: 30952088 PMCID: PMC6710113 DOI: 10.1016/j.copbio.2019.03.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2019] [Revised: 02/13/2019] [Accepted: 03/01/2019] [Indexed: 12/20/2022]
Abstract
Microbial communities can perform a variety of behaviors that are useful in both therapeutic and industrial settings. Engineered communities that differ in composition from naturally occurring communities offer a unique opportunity for improving upon existing community functions and expanding the range of microbial community applications. This has prompted recent advances in various community design approaches including artificial selection procedures, reduction from existing communities, combinatorial evaluation of potential microbial combinations, and model-based in silico community optimization. Computational methods in particular offer a likely avenue toward improved synthetic community development going forward. This review introduces each class of design approach and surveys their recent applications and notable innovations, closing with a discussion of existing design challenges and potential opportunities for advancement.
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Affiliation(s)
- Alexander Eng
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195, USA
| | - Elhanan Borenstein
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195, USA; Department of Computer Science and Engineering, University of Washington, Seattle, WA 98195, USA; Blavatnik School of Computer Science, Tel Aviv University, Tel Aviv 6997801, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel; Santa Fe Institute, Santa Fe, NM 87501, USA.
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4
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Thompson RA, Trinh CT. Overflow metabolism and growth cessation in Clostridium thermocellum DSM1313 during high cellulose loading fermentations. Biotechnol Bioeng 2017; 114:2592-2604. [PMID: 28671264 DOI: 10.1002/bit.26374] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 06/25/2017] [Accepted: 06/27/2017] [Indexed: 12/31/2022]
Abstract
As a model thermophilic bacterium for the production of second-generation biofuels, the metabolism of Clostridium thermocellum has been widely studied. However, most studies have characterized C. thermocellum metabolism for growth at relatively low substrate concentrations. This outlook is not industrially relevant, however, as commercial viability requires substrate loadings of at least 100 g/L cellulosic materials. Recently, a wild-type C. thermocellum DSM1313 was cultured on high cellulose loading batch fermentations and reported to produce a wide range of fermentative products not seen at lower substrate concentrations, opening the door for a more in-depth analysis of how this organism will behave in industrially relevant conditions. In this work, we elucidated the interconnectedness of overflow metabolism and growth cessation in C. thermocellum during high cellulose loading batch fermentations (100 g/L). Metabolic flux and thermodynamic analyses suggested that hydrogen and formate accumulation perturbed the complex redox metabolism and limited conversion of pyruvate to acetyl-CoA conversion, likely leading to overflow metabolism and growth cessation in C. thermocellum. Pyruvate formate lyase (PFL) acts as an important redox valve and its flux is inhibited by formate accumulation. Finally, we demonstrated that manipulation of fermentation conditions to alleviate hydrogen accumulation could dramatically alter the fate of pyruvate, providing valuable insight into process design for enhanced C. thermocellum production of chemicals and biofuels. Biotechnol. Bioeng. 2017;114: 2592-2604. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- R Adam Thompson
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville and Oak Ridge National Laboratory, Oak Ridge, Tennessee.,BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Cong T Trinh
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville and Oak Ridge National Laboratory, Oak Ridge, Tennessee.,BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.,Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, Tennessee
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5
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Yan BH, Selvam A, Wong JWC. Innovative method for increased methane recovery from two-phase anaerobic digestion of food waste through reutilization of acidogenic off-gas in methanogenic reactor. BIORESOURCE TECHNOLOGY 2016; 217:3-9. [PMID: 27039352 DOI: 10.1016/j.biortech.2016.03.116] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 03/17/2016] [Accepted: 03/21/2016] [Indexed: 06/05/2023]
Abstract
In this study, the performance of a two-phase anaerobic digestion reactor treating food waste with the reutilization of acidogenic off-gas was investigated with the objective to improve the hydrogen availability for the methanogenic reactor. As a comparison a treatment without off-gas reutilization was also set up. Results showed that acidogenic off-gas utilization in the upflow anaerobic sludge blanket (UASB) reactor increased the methane recovery up to 38.6%. In addition, a 27% increase in the production of cumulative chemical oxygen demand (COD) together with an improved soluble microbial products recovery dominated by butyrate was observed in the acidogenic leach bed reactor (LBR) with off-gas reutilization. Of the increased methane recovery, ∼8% was contributed by the utilization of acidogenic off-gas in UASB. Results indicated that utilization of acidogenic off-gas in methanogenic reactor is a viable technique for improving overall methane recovery.
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Affiliation(s)
- Bing Hua Yan
- Lab of Waste Valorisation and Water Reuse, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China; Sino-Forest Applied Research Centre for Pearl River Delta Environment, Department of Biology, Hong Kong Baptist University, Hong Kong Special Administrative Region
| | - Ammaiyappan Selvam
- Sino-Forest Applied Research Centre for Pearl River Delta Environment, Department of Biology, Hong Kong Baptist University, Hong Kong Special Administrative Region
| | - Jonathan W C Wong
- Sino-Forest Applied Research Centre for Pearl River Delta Environment, Department of Biology, Hong Kong Baptist University, Hong Kong Special Administrative Region.
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Beckers L, Masset J, Hamilton C, Delvigne F, Toye D, Crine M, Thonart P, Hiligsmann S. Investigation of the links between mass transfer conditions, dissolved hydrogen concentration and biohydrogen production by the pure strain Clostridium butyricum CWBI1009. Biochem Eng J 2015. [DOI: 10.1016/j.bej.2015.01.008] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Benomar S, Ranava D, Cárdenas ML, Trably E, Rafrafi Y, Ducret A, Hamelin J, Lojou E, Steyer JP, Giudici-Orticoni MT. Nutritional stress induces exchange of cell material and energetic coupling between bacterial species. Nat Commun 2015; 6:6283. [PMID: 25704114 DOI: 10.1038/ncomms7283] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 01/12/2015] [Indexed: 12/24/2022] Open
Abstract
Knowledge of the behaviour of bacterial communities is crucial for understanding biogeochemical cycles and developing environmental biotechnology. Here we demonstrate the formation of an artificial consortium between two anaerobic bacteria, Clostridium acetobutylicum (Gram-positive) and Desulfovibrio vulgaris Hildenborough (Gram-negative, sulfate-reducing) in which physical interactions between the two partners induce emergent properties. Molecular and cellular approaches show that tight cell-cell interactions are associated with an exchange of molecules, including proteins, which allows the growth of one partner (D. vulgaris) in spite of the shortage of nutrients. This physical interaction induces changes in expression of two genes encoding enzymes at the pyruvate crossroads, with concomitant changes in the distribution of metabolic fluxes, and allows a substantial increase in hydrogen production without requiring genetic engineering. The stress induced by the shortage of nutrients of D. vulgaris appears to trigger the interaction.
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Affiliation(s)
- Saida Benomar
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13009 Marseille, France
| | - David Ranava
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13009 Marseille, France
| | - María Luz Cárdenas
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13009 Marseille, France
| | - Eric Trably
- INRA, UR050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France
| | - Yan Rafrafi
- INRA, UR050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France
| | - Adrien Ducret
- Laboratoire de Chimie Bactérienne, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 13009 Marseille, France
| | - Jérôme Hamelin
- INRA, UR050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France
| | - Elisabeth Lojou
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13009 Marseille, France
| | - Jean-Philippe Steyer
- INRA, UR050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France
| | - Marie-Thérèse Giudici-Orticoni
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS-Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13009 Marseille, France
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Rittmann S, Herwig C. A comprehensive and quantitative review of dark fermentative biohydrogen production. Microb Cell Fact 2012; 11:115. [PMID: 22925149 PMCID: PMC3443015 DOI: 10.1186/1475-2859-11-115] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 08/03/2012] [Indexed: 01/25/2023] Open
Abstract
Biohydrogen production (BHP) can be achieved by direct or indirect biophotolysis, photo-fermentation and dark fermentation, whereof only the latter does not require the input of light energy. Our motivation to compile this review was to quantify and comprehensively report strains and process performance of dark fermentative BHP. This review summarizes the work done on pure and defined co-culture dark fermentative BHP since the year 1901. Qualitative growth characteristics and quantitative normalized results of H2 production for more than 2000 conditions are presented in a normalized and therefore comparable format to the scientific community.Statistically based evidence shows that thermophilic strains comprise high substrate conversion efficiency, but mesophilic strains achieve high volumetric productivity. Moreover, microbes of Thermoanaerobacterales (Family III) have to be preferred when aiming to achieve high substrate conversion efficiency in comparison to the families Clostridiaceae and Enterobacteriaceae. The limited number of results available on dark fermentative BHP from fed-batch cultivations indicates the yet underestimated potential of this bioprocessing application. A Design of Experiments strategy should be preferred for efficient bioprocess development and optimization of BHP aiming at improving medium, cultivation conditions and revealing inhibitory effects. This will enable comparing and optimizing strains and processes independent of initial conditions and scale.
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Affiliation(s)
- Simon Rittmann
- Institute of Chemical Engineering, Research Area Biochemical Engineering, Gumpendorferstraße 1a, Vienna University of Technology, Vienna, 1060, Austria
| | - Christoph Herwig
- Institute of Chemical Engineering, Research Area Biochemical Engineering, Gumpendorferstraße 1a, Vienna University of Technology, Vienna, 1060, Austria
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9
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Tekucheva DN, Tsygankov AA. Combined biological hydrogen-producing systems: A review. APPL BIOCHEM MICRO+ 2012. [DOI: 10.1134/s0003683812040114] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Zeidan AA, Rådström P, van Niel EWJ. Stable coexistence of two Caldicellulosiruptor species in a de novo constructed hydrogen-producing co-culture. Microb Cell Fact 2010; 9:102. [PMID: 21192828 PMCID: PMC3022713 DOI: 10.1186/1475-2859-9-102] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2010] [Accepted: 12/30/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Mixed culture enrichments have been used frequently for biohydrogen production from different feedstock. In spite of the several advantages offered by those cultures, they suffer poor H2 yield. Constructing defined co-cultures of known H2 producers may offer a better performance than mixed-population enrichments, while overcoming some of the limitations of pure cultures based on synergies among the microorganisms involved. RESULTS The extreme thermophiles Caldicellulosiruptor saccharolyticus DSM 8903 and C. kristjanssonii DSM 12137 were combined in a co-culture for H2 production from glucose and xylose in a continuous-flow stirred tank reactor. The co-culture exhibited a remarkable stability over a period of 70 days under carbon-sufficient conditions, with both strains coexisting in the system at steady states of different dilution rates, as revealed by species-specific quantitative PCR assays. The two strains retained their ability to stably coexist in the reactor even when glucose was used as the sole growth-limiting substrate. Furthermore, H2 yields on glucose exceeded those of either organism alone under the same conditions, alluding to a synergistic effect of the two strains on H2 production. A maximum H2 yield of 3.7 mol (mol glucose)(-1) was obtained by the co-culture at a dilution rate of 0.06 h(-1); a higher yield than that reported for any mixed culture to date. A reproducible pattern of population dynamics was observed in the co-culture under both carbon and non-carbon limited conditions, with C. kristjanssonii outgrowing C. saccharolyticus during the batch start-up phase and prevailing at higher dilution rates. A basic continuous culture model assuming the ability of C. saccharolyticus to enhance the growth of C. kristjanssonii could mimic the pattern of population dynamics observed experimentally and provide clues to the nature of interaction between the two strains. As a proof, the cell-free growth supernatant of C. saccharolyticus was found able to enhance the growth of C. kristjanssonii in batch culture through shortening its lag phase and increasing its maximum biomass concentration by ca. 18%. CONCLUSIONS This study provides experimental evidence on the stable coexistence of two closely related organisms isolated from geographically-distant habitats under continuous operation conditions, with the production of H2 at high yields. An interspecies interaction is proposed as the reason behind the remarkable ability of the two Caldicellulosiruptor strains to coexist in the system rather than only competing for the growth-limiting substrate.
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Affiliation(s)
- Ahmad A Zeidan
- Applied Microbiology, Lund University, Getingevägen 60, SE-222 41 Lund, Sweden.
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Bader J, Mast-Gerlach E, Popović MK, Bajpai R, Stahl U. Relevance of microbial coculture fermentations in biotechnology. J Appl Microbiol 2009; 109:371-387. [PMID: 20070440 DOI: 10.1111/j.1365-2672.2009.04659.x] [Citation(s) in RCA: 186] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The purpose of this article is to review coculture fermentations in industrial biotechnology. Examples for the advantageous utilization of cocultures instead of single cultivations include the production of bulk chemicals, enzymes, food additives, antimicrobial substances and microbial fuel cells. Coculture fermentations may result in increased yield, improved control of product qualities and the possibility of utilizing cheaper substrates. Cocultivation of different micro-organisms may also help to identify and develop new biotechnological substances. The relevance of coculture fermentations and the potential of improving existing processes as well as the production of new chemical compounds in industrial biotechnology are pointed out here by means of more than 35 examples.
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Affiliation(s)
- J Bader
- Technische Universität Berlin, Fachgebiet Mikrobiologie and Genetik, Seestraβe 13, Berlin, Germany
| | - E Mast-Gerlach
- Technische Universität Berlin, Fachgebiet Mikrobiologie and Genetik, Seestraβe 13, Berlin, Germany
| | - M K Popović
- Beuth Hochschule für Technik, Fachbereich Biotechnologie, Seestraβe 64, Berlin, Germany
| | - R Bajpai
- Chemical Engineering Department, University of Louisiana at Lafayette, Lafayette, LA, USA
| | - U Stahl
- Technische Universität Berlin, Fachgebiet Mikrobiologie and Genetik, Seestraβe 13, Berlin, Germany
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Wang MY, Olson BH, Chang JS. Relationship among growth parameters for Clostridium butyricum, hydA gene expression, and biohydrogen production in a sucrose-supplemented batch reactor. Appl Microbiol Biotechnol 2008; 78:525-32. [DOI: 10.1007/s00253-007-1317-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Revised: 12/04/2007] [Accepted: 12/06/2007] [Indexed: 11/28/2022]
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13
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Temudo MF, Kleerebezem R, van Loosdrecht M. Influence of the pH on (open) mixed culture fermentation of glucose: A chemostat study. Biotechnol Bioeng 2007; 98:69-79. [PMID: 17657773 DOI: 10.1002/bit.21412] [Citation(s) in RCA: 165] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Catabolic products from anaerobic fermentation processes are potentially of industrial interest. The volatile fatty acids and alcohols produced can be used as building blocks in chemical processes or applied directly as substrates in a mixed culture process to produce bioplastics. Development of such applications requires a predictable and controllable product spectrum of the fermentation process. The aim of the research described in this paper was (i) to investigate the product spectrum of an open mixed culture fermentation (MCF) process as a function of the pH, using glucose as substrate, and (ii) to relate the product spectrum obtained to generalized biochemical and thermodynamic considerations. A chemostat was operated under carbon and energy limitation in order to investigate the pH effect on the product spectrum in a MCF process. A transition from CO(2)/H(2) production at lower pH values to formate production at higher pH values was observed. The ratio of CO(2)/H(2) versus formate production was found to be related to the thermodynamics of formate dehydrogenation to CO(2)/H(2). This transition was associated with a shift in the catabolic products, from butyrate and acetate to ethanol and acetate, likely due to a decrease in the oxidation state of the electron carriers in the cell. The product spectrum of the MCF process as a function of the pH could largely be explained using general biochemical considerations.
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Affiliation(s)
- Margarida F Temudo
- Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands
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Collet C, Girbal L, Péringer P, Schwitzguébel JP, Soucaille P. Metabolism of lactose by Clostridium thermolacticum growing in continuous culture. Arch Microbiol 2006; 185:331-9. [PMID: 16508746 DOI: 10.1007/s00203-006-0098-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2005] [Revised: 01/18/2006] [Accepted: 02/07/2006] [Indexed: 11/24/2022]
Abstract
The objective of the present study was to characterize the metabolism of Clostridium thermolacticum, a thermophilic anaerobic bacterium, growing continuously on lactose (10 g l(-1)) and to determine the enzymes involved in the pathways leading to the formation of the fermentation products. Biomass and metabolites concentration were measured at steady-state for different dilution rates, from 0.013 to 0.19 h(-1). Acetate, ethanol, hydrogen and carbon dioxide were produced at all dilution rates, whereas lactate was detected only for dilution rates below 0.06 h(-1). The presence of several key enzymes involved in lactose metabolism, including beta-galactosidase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate:ferredoxin oxidoreductase, acetate kinase, ethanol dehydrogenase and lactate dehydrogenase, was demonstrated. Finally, the intracellular level of NADH, NAD+, ATP and ADP was also measured for different dilution rates. The production of ethanol and lactate appeared to be linked with the re-oxidation of NADH produced during glycolysis, whereas hydrogen produced should come from reduced ferredoxin generated during pyruvate decarboxylation. To produce more hydrogen or more acetate from lactose, it thus appears that an efficient H2 removal system should be used, based on a physical (membrane) or a biological approach, respectively, by cultivating C. thermolacticum with efficient H2 scavenging and acetate producing microorganisms.
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Affiliation(s)
- Christophe Collet
- Laboratory for Environmental Biotechnology (LBE), Swiss Federal Institute of Technology Lausanne (EPFL), Station 6, 1015, Lausanne, Switzerland
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