Abstract
The uptake hydrogenase mutant (ΔHup) cells of heterocystous cyanobacterium Nostoc sp. PCC 7422 photobiologically accumulated H2 to about 30% in the presence of O2 evolved. N2 gas concentration of 0.5-1% in Ar was optimal for photobiological H2 accumulation in both the heterocyst induction (0-2 days after combined-nitrogen step-down) and the hydrogen production (thereafter) phases. We studied the effects of CO2 concentration (0.03%, 1%, 5% CO2) in 0.5% N2 in Ar, and found that 5% CO2 was optimal for H2 accumulation in both phases. A culture could produce hydrogen for more than 60 days without changing the culture medium and with renewing the gas phase about once a week. H2 accumulation experiments are routinely carried out using Fernbach flasks capped with butyl rubber stoppers, but the inner pressure rises with time by photobiological production of H2 and O2, and by absorption/emission of CO2. The use of transparent gas-barrier Besela plastic bags (Kureha Co.) allows us to evaluate photobiological H2 accumulation under the ambient pressure. We have produced gas-sampling devices for collecting sample gases for studies of the time course H2 accumulation.
