Elucidating acetogenic H2 consumption in dark fermentation using flux balance analysis

Area of Science:

• Biotechnology
• Biochemical Engineering
• Microbial Metabolism

Background:

• Dark fermentation is a promising method for biological hydrogen (H2) production.
• Understanding microbial metabolic pathways is crucial for optimizing H2 yields.
• Acetogenic H2 consumption can limit overall H2 production efficiency.

Purpose of the Study:

• To estimate the activity of acetogenic H2-consuming reactions using flux balance analysis (FBA).
• To investigate the effect of substrate concentration on H2 yield and associated metabolic fluxes.
• To clarify the role of acetate production in H2 yield during dark fermentation.

Main Methods:

• Flux balance analysis (FBA) was employed to model microbial metabolism.
• Experimental data from varying substrate concentrations (10, 20, 30 g COD/L) were integrated into the FBA.
• Key metabolic fluxes, including hydrogenase and acetate production pathways, were quantified.

Main Results:

• Hydrogenase activity (ferredoxin-dependent) was highest at the lowest substrate concentration (10 g COD/L).
• The H2-reutilizing pathway (R17: 4H2 + 2CO2 → CH3COOH) flux significantly increased as substrate concentration decreased.
• Acetate production exhibited a negligible or negative correlation with final H2 yield, challenging conventional understanding.

Conclusions:

• Substrate concentration significantly influences H2 consumption pathways in dark fermentation.
• Optimizing conditions to favor H2 production over H2 consumption is critical for maximizing H2 yield.
• The role of acetate production in H2 yield requires re-evaluation in the context of specific microbial consortia and fermentation conditions.