Abstract
N2-fixing cyanobacteria can produce hydrogen as an inevitable by-product of nitrogenase reaction. In order to improve photobiological H2 productibity by decreasing reabsorption of hydrogen, we have created three hydrogenase mutants from Anabaena PCC 7120 (ΔhupL, ΔhoxH, ΔhupL/ΔhoxH) and shown that the ΔhupL and ΔhupL/ΔhoxH produced H2 at a rate 4-7 times that of wild-type. However, such high production activity stage lasted for only about 10 hours. Homocitrate is liganded to the catalytic MoFe7S9 cluster in nitrogenase, and inactivation of homocitrate synthase decreases efficiency of nitrogen fixation leading to increased hydrogen production in Klebsiella pneumoniae. We have created three mutants (ΔnifV1, ΔnifV2, ΔnifV1/ΔnifV2) on the ΔhupL background. One of the mutants showed higher and more lasting hydrogen productivity over the parental strain under Ar or N2.
