Escherichia coli hydrogen gas production from glycerol: Effects of external formate

Hydrogen gas (H2) production was studied in bacteria cultured at different pH conditions, and on different carbon substrates. H2 production by Escherichia coli was first studied during glycerol fermentation when external formate (10 mM) was supplemented. Changes in H2 production rate (VH2) were determined when in the assays glycerol and/or formate were supplemented at pH 7.5 and pH 6.5, using single and double mutants coding large subunits of different hydrogenases (Hyd-1, Hyd-2 and Hyd-3) as well as selC (coding for formate dehydrogenases), hyaB hybC (coding for large subunits of Hyd-1 and Hyd-2, respectively) selC or hyaB hybC hycE (coding for large subunit of Hyd-3) triple mutants at both pHs. The results point out that Hyd-3 becomes mainly responsible for H2 production by E. coli during glycerol fermentation when external formate is added; Hyd-4 can also contribute to H2 production. Besides, in the glycerol supplemented assays, three hydrogenases can work in H2 producing mode and only deletion of three of them decreases the production of H2 which might be due to disturbance of H2 cycling. This is of significance in application of different carbon sources in renewable energy production technology using bacteria.