Metabolic pathway and flux analysis of H₂ production by an anaerobic mixed culture

A metabolic model is proposed for H₂ production from a mixed culture growing on glucose. The model based on the metabolism of Firmicutes, predominant phylum, includes substantial changes compared with previous models. Full TCA cycle and a bifurcating dehydrogenase that uses ferredoxin and participates in the reduction of crotonyl-coenzyme-A are introduced. Pathway analysis suggests that H₂ yields greater than those reported are possible redirecting the flow of glucose to the pentose phosphate pathway instead of glycolysis. H₂ yield as high as 10 mol H₂/mol glucose is metabolically possible if the H₂ pressure is sufficiently low. The adequacy was determined by metabolic flux analysis. Experimental yield of 2.23 mol H₂/mol glucose are contained in the solution space and shows that growth is suboptimal for the mixed culture used. Data suggest that H₂ yields can be improved by knocking out both competing reactions and the phosphoglucose isomerase. Higher NADPH₂ production could increase H₂ production even though it would reduce growth rate.