Disruption of the uptake hydrogenase gene, but not of the bidirectional hydrogenase gene, leads to enhanced photobiological hydrogen production by the nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120

Abstract.

In order to determine the effects of the deletion of hydrogenase genes on nitrogenase-based photobiological H₂ productivity by heterocystous N₂-fixing cyanobacteria, we have constructed three hydrogenase mutants from Anabaena sp. PCC 7120: hupL ^– (deficient in the uptake hydrogenase), hoxH ^– (deficient in the bidirectional hydrogenase), and hupL ^–/hoxH ^– (deficient in both genes). The hupL ^– mutant produced H₂ at a rate four to seven times that of the wild-type under optimal conditions. The hoxH ^– mutant produced significantly lower amounts of H₂ and had slightly lower nitrogenase activity than wild-type. H₂ production by the hupL ^–/hoxH ^– mutant was slightly lower than, but almost equal to, that of the hupL ^– mutant. The efficiency of light energy conversion to H₂ by the hupL ^– mutant at its highest H₂ production stage was 1.2% at an actinic visible light intensity of 10 W/m² (PAR) under argon atmosphere. These results indicate that deletion of the hupL gene could be employed as a source for further improvement of H₂ production in a nitrogenase-based photobiological H₂ production system.