MUTANTS OF THE CYANOBACTERIUM ANABAENA-VARIABILIS ALTERED IN HYDROGENASE ACTIVITIES

Two mutants of the cyanobacterium Anabaena variabilis impaired in the utilization or formation of molecular hydrogen have been obtained by n itroso-guanidine mutagenesis. Cultures of both mutants did not show al terations in the growth characteristics or in the heterocysts frequenc y but evolved molecular hydrogen from nitrogenase with enhanced rates. Activity measurements in extracts showed that one mutant (PK84) did n ot perform Na2S2O4-dependent H-2-formation and was, therefore, unable to express an active bidirectional hydrogenase. Both mutants (PK84, PK 17R) were characterized by lower activity of phenazine-methosulphate-d ependent H-2-uptake when extracts were assayed from younger cultures. In older cells, particularly when grown with nitrate in the medium, th is H-2-uptake activity was, however, enhanced, Both mutants are likely affected in regulatory hydrogenase genes. The mutant PK84 offers pers pectives for potential applications in solar energy conversion program s.