Mutants of the Cyanobacterium Anabaena variabilis Altered in Hydrogenase Activities

Abstract

Abstract Two mutants of the cyanobacterium Anabaena variabilis impaired in the utilization or formation of molecular hydrogen have been obtained by nitroso-guanidine mutagenesis. Cul­tures of both mutants did not show alterations in the growth characteristics or in the hetero­cysts frequency but evolved molecular hydrogen from nitrogenase with enhanced rates. Ac­tivity measurements in extracts showed that one mutant (PK84) did not perform Na2S2O4- dependent H2-formation and was, therefore, unable to express an active bidirectional hydro­genase. Both mutants (PK84, PK 17R) were characterized by lower activity of phenazine-methosulphate-dependent H2-uptake when extracts were assayed from younger cultures. In older cells, particularly when grown with nitrate in the medium , this H2-uptake activity was, how ever, enhanced. Both mutants are likely affected in regulatory hydrogenase genes. The mutant PK84 offers perspectives for potential applications in solar energy conversion programs.