Effect of HupS inactivation on the sustainability of hydrogen production and nitrogenase activity. Comparison of hydrogen production (A) and nitrogenase activity (B) between wild type and ∆hupS strains of Anabaena siamensis TISTR 8012 was done after growth in BG110 medium for 4 days at 40 μEm-2s-1. The collected cells were determined for hydrogen production and nitrogenase activity after incubation for various times under continuous illumination of high light intensity at 200 μE m-2s-1 and anaerobic condition. Means ± S.D. (n=3).