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

Abstract

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.