초록
The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 contains a single bidirectional NiFe-Hox-hydrogenase, which evolves hydrogen under certain environmental conditions. The nitrate assimilation pathway is a potential competing pathway that may reduce the electron flow to the hydrogenase and thereby limit hydrogen production. To improve H<SUB>2</SUB> production, the nitrate assimilation pathway was disrupted by genetic engineering to redirect the electron flow towards the Hox-hydrogenase. Mutant strains disrupted in either nitrate reductase (ΔnarB) or nitrite reductase (ΔnirA) or both nitrate reductase and nitrite reductase (ΔnarB:ΔnirA) were constructed and tested for their ability to produce hydrogen. H<SUB>2</SUB> production and Hox-hydrogenase activities in all the mutant strains were higher than those in wild-type. Highest H<SUB>2</SUB> production was observed in the ΔnarB:ΔnirA strain. Small changes were observed for Hox-hydrogenase enzyme activities and only minor changes in transcript levels of hoxH and hoxY were not correlated with H<SUB>2</SUB> production. The results suggest that the high rate of H<SUB>2</SUB> production observed in the ΔnarB:ΔnirA strain of the cyanobacterium Synechocystis sp. strain PCC 6803 is the result of redirecting the electron supply from the nitrate assimilation pathway, through genetic engineering, towards the Hox-hydrogenase.