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

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.

Electricity-driven metabolic shift through direct electron uptake by electroactive heterotroph Clostridiumpasteurianum

“…Microbial growth was checked by absorbance at 600 nm using a Shimadzu UVmini-1240 spectrophotometer (Kyoto, Japan). For a purpose of electron and carbon balance calculation, final biomass was checked by chemical oxygen demand (COD, mg/L unit) induced by subtract soluble COD from total COD using COD vials (C-mac, South Korea, concentration range of 10–1,500 mg/L)37. The composition of hydrogen and carbon dioxide in the biogas was analyzed using GC-TCD (Agilent Technologies 6890 N).…”

Comparison of acetate-butyrate and acetate-ethanol metabolic pathway in biohydrogen production

“…'s study. [92125] These results demonstrated that actually growing of cells and adenosine triphosphate synthesis. [26] For all batch tests, the mass balance recovery based on the e − eq were closed within 5.2%–13.5% and depicted good detection of end products.…”

“…[1721] The high acetate production suggested that the fermenting bacteria could efficiently conserve energy through acetate production. [1722] In all batch tests, the portion of biohydrogen was fluctuated from 11% to 23% and the little portion of electron sink was related to propionate (<2%).…”

“…The lower biohydrogen production during KOH pretreatment presumably related to electron flows from reduced ferredoxin to NAD + and produced NADH 2 instead of biohydrogen. [1821] The reduction of acetyl-CoA can produce ethanol and butyrate and lead to NADH 2 consumption and may result in lower H 2 production. [18]…”

Simultaneous Decolorization and Biohydrogen Production from Xylose by Klebsiella oxytoca GS-4-08 in the Presence of Azo Dyes with Sulfonate and Carboxyl Groups

“…One of the cellulose hydrolysates, i.e., glucose, could be easily fermented to hydrogen gas (14)(15)(16). However, the other abundant hemicellulose hydrolysis product, i.e., xylose, was less efficient as a precursor for biohydrogen production both in pure and in mixed cultures (17)(18)(19).…”