Identification of genes required for hydrogenase activity in Chlamydomonas reinhardtii

The eukaryotic green alga, Chlamydomonas reinhardtii, produces H₂ under anaerobic conditions, in a reaction catalysed by an [FeFe]-hydrogenase. To identify genes that influence H₂ production in C. reinhardtii, a library of 6000 colonies on agar plates was screened with sensitive chemochromic H₂-sensor films for clones defective in H₂ production. Two mutants of particular interest were fully characterized. One mutant, hydEF-1, is unable to assemble an active [FeFe]-hydrogenase. This is the first reported C. reinhardtii mutant that is not capable of producing any H₂. The second mutant, sta7-10, is not able to accumulate insoluble starch and has significantly lowered H₂-photoproduction rates in comparison with the wild-type. In hydEF-1, anaerobiosis induces transcription of the two reported C. reinhardtii hydrogenase genes, HydA1 and HydA2, indicating a normal transcriptional response to anaerobiosis. In contrast, the transcription of both hydrogenase genes in sta7-10 is significantly attenuated.