Abstract
For improvement and better sustainability of photobiological hydrogen production based on nitrogenase and photosynthesis by cyanobacteria, we have created several hydrogenase and homocitrate synthase mutants. The mutant of Nostoc sp. PCC 7120 disrupted in uptake hydrogenase gene (ΔhupL) showed improved hydrogen production activity over the wild-type. Nostoc sp. PCC 7422 has high nitrogenase activity, and the ΔhupL cells were able to accumulate hydrogen to about 30% (v/v) in 3 to 8 days, with the efficiency of light energy conversion into hydrogen of as high as 3.7% vs visible light. In these mutants, the high hydrogen production activity stages were relatively short-lived, lasting for 10-20 hours. The mutant (ΔnifV1) disrupted in one of the homocitrate synthase genes with PCC 7120 ΔhupL as the parent showed improved sustainability of production. Addition of low concentrations of CO2 and N2 to Ar gas sometimes improved the sustainability.
