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H2 Yield (h2 + yield)
Selected AbstractsOptimization of glutamate concentration and pH for H2 production from volatile fatty acids by Rhodopseudomonas capsulataLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2005X.-Y. Shi Abstract Aims:, This study attempted to employ response surface methodology (RSM) to evaluate the effects of glutamate concentration and pH on H2 production from volatile fatty acids by Rhodopseudomonas capsulata. Methods and Results:, A mixture of acetate, propionate and butyrate was used as a carbon source for the H2 production by R. capsulata. The H2 yield and H2 production rate were strongly affected by the glutamate concentration, pH and their interaction. The predicted maximum H2 yield of 0·534 was obtained when glutamate concentration and pH were 6·56 mmol l,1 and 7·29 respectively. On the contrary, the maximum H2 production rate of 18·72 ml l,1 h,1 was achieved at a glutamate concentration of 7·01 mmol l,1 and pH 7·31. Conclusions:, Taking H2 yield and H2 production rate together into account, a glutamate concentration of 6·56,7·01 mmol l,1 and pH of 7·29,7·31 should be selected for H2 production from a mixture of acetate, propionate and butyrate by R. capsulata. Significance and Impact of the Study:, The RSM was a useful tool for maximizing H2 production by photosynthetic bacteria (PSB). [source] An electron-flow model can predict complex redox reactions in mixed-culture fermentative BioH2: Microbial ecology evidenceBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Hyung-Sool Lee Abstract 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. Biotechnol. Bioeng. 2009; 104: 687,697 © 2009 Wiley Periodicals, Inc. [source] Evaluation of metabolism using stoichiometry in fermentative biohydrogenBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2009Hyung-Sool Lee Abstract We first constructed full stoichiometry, including cell synthesis, for glucose mixed-acid fermentation at different initial substrate concentrations (0.8,6 g-glucose/L) and pH conditions (final pH 4.0,8.6), based on experimentally determined electron-equivalent balances. The fermentative bioH2 reactions had good electron closure (,9.8 to +12.7% for variations in glucose concentration and ,3 to +2% for variations in pH), and C, H, and O errors were below 1%. From the stoichiometry, we computed the ATP yield based on known fermentation pathways. Glucose-variation tests (final pH 4.2,5.1) gave a consistent fermentation pattern of acetate,+,butyrate,+,large H2, while pH significantly shifted the catabolic pattern: acetate,+ butyrate,+,large H2 at final pH 4.0, acetate,+,ethanol,+ modest H2 at final pH 6.8, and acetate,+,lactate,+,trivial H2 at final pH 8.6. When lactate or propionate was a dominant soluble end product, the H2 yield was very low, which is in agreement with the theory that reduced ferredoxin (Fdred) formation is required for proton reduction to H2. Also consistent with this hypothesis is that high H2 production correlated with a high ratio of butyrate to acetate. Biomass was not a dominant sink for electron equivalents in H2 formation, but became significant (12%) for the lowest glucose concentration (i.e., the most oligotrophic condition). The fermenting bacteria conserved energy similarly at ,3 mol ATP/mol glucose (except 0.8 g-glucose/L, which had ,3.5 mol ATP/mol glucose) over a wide range of H2 production. The observed biomass yield did not correlate with ATP conservation; low observed biomass yields probably were caused by accelerated rates of decay or production of soluble microbial products. Biotechnol. Bioeng. 2009; 102: 749,758. © 2008 Wiley Periodicals, Inc. [source] Multicomponent cellulase production by Cellulomonas biazotea NCIM-2550 and its applications for cellulosic biohydrogen productionBIOTECHNOLOGY PROGRESS, Issue 2 2010Ganesh D. Saratale Abstract Among four cellulolytic microorganisms examined, Cellulomonas biazotea NCIM-2550 can grow on various cellulosic substrates and produce reducing sugar. The activity of cellulases (endoglucanase, exoglucanase, and cellobiase), xylanase, amylase, and lignin class of enzymes produced by C. biazotea was mainly present extracellularly and the enzyme production was dependent on cellulosic substrates (carboxymethyl cellulose [CMC], sugarcane bagasse [SCB], and xylan) used for growth. Effects of physicochemical conditions on cellulolytic enzyme production were systematically investigated. Using MnCl2 as a metal additive significantly induces the cellulase enzyme system, resulting in more reducing sugar production. The efficiency of fermentative conversion of the hydrolyzed SCB and xylan into clean H2 energy was examined with seven H2 -producing pure bacterial isolates. Only Clostridiumbutyricum CGS5 exhibited efficient H2 production performance with the hydrolysate of SCB and xylan. The cumulative H2 production and H2 yield from using bagasse hydrolysate (initial reducing sugar concentration = 1.545 g/L) were approximately 72.61 mL/L and 2.13 mmol H2/g reducing sugar (or 1.91 mmol H2/g cellulose), respectively. Using xylan hydrolysate (initial reducing sugar concentration = 0.345 g/L) as substrate could also attain a cumulative H2 production and H2 yield of 87.02 mL/L and 5.03 mmol H2/g reducing sugar (or 4.01 mmol H2/g cellulose), respectively. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||