RELATIONSHIP BETWEEN THE PHOTOPRODUCTION OF HYDROGEN AND THE ACCUMULATION OF PHB IN NONSULFUR PURPLE BACTERIA

Wild-type cells of Rhodobacter sphaeroides and Rhodospirillum rubrum strains Ha and S1 as well as mutant cells defective in the synthesis of poly-(3-hydroxybutyric acid) (PHB), were used to study the competition between PHB accumulation and photoproduction of hydrogen for reducing equivalents, Mutants were isolated after transposon (Tn.5) or N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. The PHB-defective mutants of R. sphaeroides lacked PHB synthase activity. In two mutants Tn5 was inserted in the PHB synthase gene. No mutants occurred that lacked the activity of beta-ketothiolase or acetoacetyl-coenzyme A reductase. Pronounced competitive effects occurred only with acetate as the organic substrate. With other organic acids or sugars, which are less readily converted to PHB than acetate, competitive effects were not significant or absent.