Beneficial knockouts in Escherichia coli for producing hydrogen from glycerol

Glycerol is an inexpensive and abundant source for biofuel production on a large scale. Escherichia coli is a robust bacterium for producing hydrogen; however, its hydrogen productivity from glycerol is low. In this study, we conducted random transposon mutagenesis to identify uncharacterized genes whose inactivation is beneficial for hydrogen production from glycerol. Through screening, four mutant strains were found that are able to have from 1.3- to 1.6-fold higher hydrogen productivity (μmol H₂/mg protein) than that of their parent strain (p < 0.05). These mutations were identified as aroM, gatZ, ycgR, and yfgI. The hydrogen yield (mol H₂/mol glycerol consumed) of the aroM, gatZ, ycgR, and yfgI strains was 1.7-, 1.4-, 2.4-, and 2.1-fold higher than that of their parent strain, respectively. Moreover, a single disruption in these genes resulted in a faster cell growth and glycerol consumption under anaerobic conditions. In E. coli, AroM is predicted to be involved in the shikimate pathway, GatZ is tagatose-1,6-bisphosphate aldolase 2 which converts dihydroxyacetone phosphate to 1,6-biphosphate, and YcgR acts as a molecular brake limiting the swimming speed and ATP consumption. So far, the function of YfgI in general and in hydrogen production in particular remains unknown.