Metabolic Flux Analysis of Clostridium thermosuccinogenes

Sridhar, Jayanth; Eiteman, Mark A.

doi:10.1385/abab:94:1:51

Cited by 47 publications

(38 citation statements)

References 49 publications

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“…A similar metabolic flux analysis of C. thermosuccinogenes fermentation also showed that the flux of carbon towards lactate formation decreased significantly with increasing the pH from 6.50 to 7.25 (Sridhar and Eiteman, 2001). The metabolic pathway shift can be attributed to the control of balancing the redox potential or NADH and NAD + .…”

Section: Effect Of Ph On Metabolic Pathwaymentioning

confidence: 59%

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

Zhu

Yang

2004

Journal of Biotechnology

212

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The effect of pH (between 5.0 and 6.3) on butyric acid fermentation of xylose by Clostridium tyrobutyricum was studied. At pH 6.3, the fermentation gave a high butyrate production of 57.9 g l −1 with a yield of 0.38-0.59 g g −1 xylose and a reactor productivity up to 3.19 g l −1 h −1 . However, at low pHs (<5.7), the fermentation produced more acetate and lactate as the main products, with only a small amount of butyric acid. The metabolic shift from butyrate formation to lactate and acetate formation in the fermentation was found to be associated with changes in the activities of several key enzymes. The activities of phosphotransbutyrylase (PTB), which is the key enzyme controlling butyrate formation, and NAD-independent lactate dehydrogenase (iLDH), which catalyzes the conversion of lactate to pyruvate, were higher in cells producing mainly butyrate at pH 6.3. In contrast, cells at pH 5.0 had higher activities of phosphotransacetylase (PTA), which is the key enzyme controlling acetate formation, and lactate dehydrogenase (LDH), which catalyzes the conversion of pyruvate to lactate. Also, PTA was very sensitive to the inhibition by butyric acid. Difference in the specific metabolic rate of xylose at different pHs suggests that the balance in NADH is a key in controlling the metabolic pathway used by the cells in the fermentation.

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Section: Effect Of Ph On Metabolic Pathwaymentioning

confidence: 59%

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

Zhu

Yang

2004

Journal of Biotechnology

212

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“…A large accumulation of propionate often has been found in parallel with negligible H 2 production (Koskinen et al, 2007;Lee and Rittmann, 2009;Ren et al, 1997), which is consistent to our experimental result at final pH 4.0. Since propionate is produced at the pyruvate node or the upper node in glycolysis, pathway B or C in Figure 1 (Schlegel, 1993;Sridhar and Eiteman, 2001), Fd red formation decreases (Saint-Amans et al, 2001;Vasconcelos et al, 1994), and this should decrease H 2 generation. It is ambiguous why ethanol accumulation reduces H 2 yield at final pH 4.0, even though ethanol synthesis from acetyl-CoA can produce Fd red , the e À donor to protons (Fig.…”

Section: Results and Discussion H 2 Yields And Distribution Of Liquidmentioning

confidence: 99%

“…An electron-flow study was performed in pure-culture fermentation using electron equivalent (e À equiv) balances and known pathways (Desvaux et al, 2001;Girbal et al, 1995a,b;Guedon et al, 1999a,b;SaintAmans et al, 2001;Sridhar and Eiteman, 2001;Thompson et al, 1984). In contrast, only a few studies have assessed electron flows experimentally in mixed culture systems (Aceves-Lara et al, 2008;Lee and Rittmann, 2009;Lee et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

An electron‐flow model can predict complex redox reactions in mixed‐culture fermentative BioH₂: Microbial ecology evidence

Lee

Krajmalinik-Brown

Zhang

et al. 2009

Biotech & Bioengineering

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We developed the first model for predicting community structure in mixed-culture fermentative biohydrogen production using electron flows and NADH2 balances. A key assumption of the model is that H2 is produced only via the pyruvate decarboxylation-ferredoxin-hydrogenase pathway, which is commonly the case for fermentation by Clostridium and Ethanoligenens species. We experimentally tested the model using clone libraries to gauge community structures with mixed cultures in which we did not pre-select for specific bacterial groups, such as spore-formers. For experiments having final pHs 3.5 and 4.0, where H2 yield and soluble end-product distribution were distinctly different, we established stoichiometric reactions for each condition by using experimentally determined electron equivalent balances. The error in electron balancing was only 3% at final pH 3.5, in which butyrate and acetate were dominant organic products and the H2 yield was 2.1 mol H2/mol glucose. Clone-library analysis showed that clones affiliated with Clostridium sp. BL-22 and Clostridium sp. HPB-16 were dominant at final pH 3.5. For final pH 4.0, the H2 yield was 0.9 mol H2/mol glucose, ethanol, and acetate were the dominant organic products, and the electron balance error was 13%. The significant error indicates that a second pathway for H2 generation was active. The most abundant clones were affiliated with Klebsiella pneumoniae, which uses the formate-cleavage pathway for H2 production. Thus, the clone-library analyses confirmed that the model predictions for when the pyruvate decarboxylation-ferredoxin-hydrogenase pathway was (final pH 3.5) or was not (final pH 4.0) dominant. With the electron-flow model, we can easily assess the main mechanisms for H2 formation and the dominant H2-producing bacteria in mixed-culture fermentative bioH2.

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“…Of the process parameters influencing ethanologenic fermentation, pH has been considered to be among the most important (25). The growth of anaerobic cellulolytic bacteria was particularly sensitive to low pH, and most of those strains cannot grow at pHs of Ͻ6.0 (2,20,26,27). Therefore, the pH control as applied in this study favored cell growth.…”

Section: Discussionmentioning

confidence: 97%

Continuous Cellulosic Bioethanol Fermentation by Cyclic Fed-Batch Cocultivation

Jiang

et al. 2013

Appl Environ Microbiol

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f Cocultivation of cellulolytic and saccharolytic microbial populations is a promising strategy to improve bioethanol production from the fermentation of recalcitrant cellulosic materials. Earlier studies have demonstrated the effectiveness of cocultivation in enhancing ethanolic fermentation of cellulose in batch fermentation. To further enhance process efficiency, a semicontinuous cyclic fed-batch fermentor configuration was evaluated for its potential in enhancing the efficiency of cellulose fermentation using cocultivation. Cocultures of cellulolytic Clostridium thermocellum LQRI and saccharolytic Thermoanaerobacter pseudethanolicus strain X514 were tested in the semicontinuous fermentor as a model system. Initial cellulose concentration and pH were identified as the key process parameters controlling cellulose fermentation performance in the fixed-volume cyclic fed-batch coculture system. At an initial cellulose concentration of 40 g liter ؊1 , the concentration of ethanol produced with pH control was 4.5-fold higher than that without pH control. It was also found that efficient cellulosic bioethanol production by cocultivation was sustained in the semicontinuous configuration, with bioethanol production reaching 474 mM in 96 h with an initial cellulose concentration of 80 g liter ؊1 and pH controlled at 6.5 to 6.8. These results suggested the advantages of the cyclic fed-batch process for cellulosic bioethanol fermentation by the cocultures. Bioethanol remains an important renewable energy alternative to petroleum-based liquid transportation fuels (1). While bioethanol derived from food crops such as corn and sugarcane has dominated the current biofuel market, recent efforts have focused on the conversion of lignocellulosic biomass to bioethanol, i.e., cellulosic bioethanol, which is considered to be socioeconomically and environmentally more sustainable (2, 3).However, the recalcitrance of cellulosic feedstock to bioconversion has posed a major challenge to the development of effective processes for cellulosic bioethanol, which typically include separate steps of enzymatic cellulose hydrolysis and microbial ethanologenic fermentation. One strategy to improve the cellulose utilization efficiency and then the ethanol production rate is the development of microbial consortia capable of simultaneously carrying out both cellulose hydrolysis and ethanologenic fermentation, representing an implementation of the consolidated bioprocessing (CBP) concept (4). Indeed, it has been demonstrated in earlier studies that cocultivation of cellulolytic and saccharolytic microbial populations could be successfully developed in batch cultures to improve cellulose utilization and ethanol production (5-7). Subsequent studies further identified metabolic mutualism, such as the supply of growth factors and utilization of excess metabolites, as the mechanism contributing to these improvements in ethanolic cellulose fermentation by cocultivation (5,8,9), further supporting the potential of cocultivation for enhancing cellulosic bi...

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Metabolic Flux Analysis of Clostridium thermosuccinogenes

Cited by 47 publications

References 49 publications

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

An electron‐flow model can predict complex redox reactions in mixed‐culture fermentative BioH₂: Microbial ecology evidence

Continuous Cellulosic Bioethanol Fermentation by Cyclic Fed-Batch Cocultivation

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Metabolic Flux Analysis of Clostridium thermosuccinogenes

Cited by 47 publications

References 49 publications

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

An electron‐flow model can predict complex redox reactions in mixed‐culture fermentative BioH2: Microbial ecology evidence

Continuous Cellulosic Bioethanol Fermentation by Cyclic Fed-Batch Cocultivation

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Product

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An electron‐flow model can predict complex redox reactions in mixed‐culture fermentative BioH₂: Microbial ecology evidence