Hydrogenases and photobiological hydrogen production utilizing nitrogenase system in cyanobacteria

We constructed three hydrogenase mutants from Anabaena sp. PCC 7120: ΔhupL (deficient in uptake hydrogenase), ΔhoxH (deficient in bidirectional hydrogenase), and ΔhupL/ΔhoxH (deficient in both genes), and showed that the Δhup and ΔhupL/ΔhoxH produced H2 at a rate 4–7 times that of wild-type under optimal conditions (Appl. Microbiol. Biotechnol. 58 (2002) 618). We have studied H2 producing activity of Δhup in more detail. H2 producing activity of Δhup cells was moderately improved in older cultures when 1% CO2 was added to the bubbling air. The efficiency of light energy conversion to H2 by the ΔhupL mutant at its highest H2 production stage was 1.0–1.6% at an actinic visible light intensity of lower than 50 W/m2 under argon atmosphere, and the activity lasted for at least 35 min. At 250 W/m2, H2 producing activity gradually decreased with illumination time.