Transcriptional control of hydrogen production during mixed carbon fermentation by hydrogenases 4 (hyf) and 3 (hyc) in Escherichia coli

Abstract

Escherichia coli molecular hydrogen (H2) production was studied during mixed carbon (glucose and glycerol) fermentation at pH 6.5. Wild type cells in the assays supplemented with glucose produced H2 at ~2 fold lower level than cells grown on glucose only. When compared to the wild type, H2 production in the assays added with glucose was decreased by ~2 fold in fhlA, hyfG and double fhlA hyfG mutants and by ~1.5 fold in hyaB, hybC, and double hyaB hybC mutants. However, in the assays with glycerol, no measurable H2 production was detected. Taken together, these results suggest that during mixed carbon fermentation, H2 could be produced with low efficiency via Hyd-3 and Hyd-4. This is a novel finding for Hyd-4 activity at pH 6.5. The insignificant decrease of H2 production in the strains with defects in Hyd-1 and Hyd-2 was probably due to an interaction between the Hyd enzymes and their organization in the bacterial membrane. In the glucose assays, H2 production in the wild type cells was inhibited ~2 fold by 0.3mM N,N′-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F0F1-ATPase. This inhibition was the same for fhlA and hyfG fhlA mutants but not hyaB, hybC, hyfG or hyaB hybC mutants. The results indicate that the FhlA protein coded by the fhlA gene might interact with the F0F1-ATPase. We propose that this interaction is mediated by mixed carbon fermentation.