Dissecting the roles of E. coli hydrogenases in biohydrogen production

Escherichia coli can perform at least two modes of anaerobic hydrogen metabolism and expresses at least two types of hydrogenase activity. Respiratory hydrogen oxidation is catalysed by two ‘uptake’ hydrogenase isoenzymes, hydrogenases -1 and -2, and fermentative hydrogen production is catalysed by hydrogenase-3. Harnessing and enhancing the metabolic capability of Escherichia coli to perform anaerobic mixed-acid fermentation is therefore an attractive approach for bio-hydrogen production from sugars. In this work, the effects of genetic modification of the genes encoding the uptake hydrogenases, as well as the importance of pre-culture conditions, on hydrogen production and fermentation balance were examined. In suspensions of resting cells pre-grown aerobically with formate, deletions in hydrogenase-3 abolished hydrogen production, whereas the deletion of both uptake hydrogenases improved hydrogen production by 37 % over the parent strain. Under fermentative conditions, respiratory H2 uptake activity was absent in strains lacking hydrogenase-2. The effect of a deletion in hycA on H2 production was found to be dependent upon environmental conditions, but H2 uptake was not significantly affected by this mutation.