Abstract
Some cyanobacteria produce hydrogen as an inevitable byproduct of nitrogen fixation. We have created three uptake hydrogenase mutants from Anabaena PCC7120 and shown that the ΔhupL and ΔhupL/ΔhoxH produced H2 at a rate 4-7 times that of wild-type. However, in the presence of N2, the H2 productivity is lowered because about 75% of the electron flux through nitrogenase is allocated to NH3 formation. Biochemical studies of nitrogenase from Klebsiella pneumoniae indicate that the catalytic MoFe7S9 cluster in nitrogenase binds homocitrate and that nitrogenase of homocitrate synthase gene nifV mutant catalyzes the reduction of protons more preferably than of N2 compared with that of the wild-type. In Anabaena PCC7120 genome two homocitrate synthase genes, nifV1 and nifV2, were identified. We have created three mutants (ΔnifV1, ΔnifV2, ΔnifV1/ΔnifV2) on the ΔhupL and examined their H2 productivities. The expression patterns of nifV1 and nifV2 were also analyzed by Northern blots and GFP reporters.
