Inactivation of the Escherichia coli K-12 twin-arginine translocation system promotes increased hydrogen production

The effect of deleting the genes encoding the twin-arginine translocation (Tat) system on H-2 production by Escherichia coli strain MC4100 and its formate hydrogenlyase upregulated mutant (Delta hycA) was investigated. H-2 evolution tests using two mutant strains defective in Tat transport (Delta tatC and Delta tatA-E) showed that the rate doubled from 0.88 +/- 0.28 mL H-2 mg dry weight(-1) L culture(-1) in the parental strain, to 1.70 +/- 0.15 and 1.75 +/- 0.18 mL H-2 mg dry weight(-1) L culture(-1), respectively, in the Delta tatC and Delta tatA-E strains. This increase was comparable to that of a previously characterized hydrogen over-producing E. coli strain carrying a Delta hycA allele. Construction of a tatC, Delta hycA double deletion strain did not increase hydrogen production further. Inactivation of the Tat system prevents correct assembly of the uptake hydrogenases and formate dehydrogenases in the cytoplasmic membrane and it is postulated that the subsequent loss of basal levels of respiratory-linked hydrogen and formate oxidation accounts for the observed increases in formate-dependent hydrogen evolution.