Influence of Escherichia coli hydrogenases on hydrogen fermentation from glycerol

Since the actual role of Escherichia coli hydrogenases on fermentation from glycerol has not been clear, we evaluated the effect of inactivation of each E. coli hydrogenase on cell growth, hydrogen production, organic acids production, and ethanol production. Inactivation of hydrogenase 2 and hydrogenase 3 reduced cell growth, hydrogen and succinate production as well as glycerol utilization while acetate increased. Inactivation of hydrogenase 2 in minimal medium at pH 7.5 impaired hydrogen production, but no significant effect occurred at pH 6.5 or in complex medium. Inactivation of hydrogenase 3 impaired hydrogen production in minimal and rich medium, pH 6.5 and pH 7.5 accumulating formate in all conditions. Therefore during fermentation from glycerol, hydrogenase 3 is the main hydrogenase with hydrogen synthesis activity through the formate hydrogen lyase complex. Hydrogenase 2 seems mainly required for optimum glycerol metabolism rather than hydrogen synthesis. There were no significant impacts by inactivating hydrogenase 1 and hydrogenase 4.

► Hyd-3, via FHL, is the main hydrogenase synthesizing hydrogen from glycerol.
► Hyd-2 is required for hydrogen production from glycerol at mild basic conditions.
► Hyd-2 activity seems not associated to FHL.