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

Wild-type cells of Rhodobacter sphaeroides and Rhodospirillum rubrum s trains Ha and S1 as well as mutant cells defective in the synthesis of poly-(3-hydroxybutyric acid) (PHB), were used to study the competitio n between PHB accumulation and photoproduction of hydrogen for reducin g equivalents, Mutants were isolated after transposon (Tn.5) or N-meth yl-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 th e activity of beta-ketothiolase or acetoacetyl-coenzyme A reductase. P ronounced competitive effects occurred only with acetate as the organi c substrate. With other organic acids or sugars, which are less readil y converted to PHB than acetate, competitive effects were not signific ant or absent.