Abstract
Some cyanobacteria produce H2 as a byproduct of N2 fixation. We created three hydrogenase mutants from Anabaena PCC 7120 (ΔhupL, ΔhoxH, ΔhupL/ΔhoxH), and showed that the ΔhupL produced H2 at a rate 4-7 times that of wild-type. The efficiency of light energy conversion to H2 by the ΔhupL was 1.0-1.6% at not exceeding 50 W/m2 (PAR). However, its highest activity lasts for only about 10 hours. It seems that accumulation of combined nitrogen in cells leads to decreases in nitrogenase and consequently H2 production activities, indicating a need for further improvement.
The active site of nitrogenase contains MoFe7S9 to which homocitrate is coordinated. Homocitrate is synthesized by NifV and it was reported in Klebsiella pneumoniae that the nitrogenase of nifV mutant catalyzes the reduction of protons more preferably than N2 compared with that of wild-type. We have created ΔnifV mutants by gene disruptions from Anabaena PCC7120 wild-type and the ΔhupL.
