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Wild-type cells of Rhodobacter sphaeroidesand 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 (Tn5) 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 fl-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.

The current knowledge on the structure and on the organization of polyhydroxyalkanoic acid (PHA)‐biosynthetic genes from a wide range of different bacteria, which rely on different pathways for biosynthesis of this storage polyesters, is provided. Molecular data will be shown for genes of Alcaligenes eutrophus, purple non‐sulfur bacteria, such as Rhodospirillum rubrum, purple sulfur bacteria, such as Chromatium vinosum, pseudomonads belonging to rRNA homology group I, such as Pseudomonas aeruginosa, Methylobacterium extorquens, and for the Gram‐positive bacterium Rhodococcus ruber. Three different types of PHA synthases can be distinguished with respect to their substrate specificity and structure. Strategies for the cloning of PHA synthase structural genes will be outlined which are based on the knowledge of conserved regions of PHA synthase structural genes and of the PHA‐biosynthetic routes in bacteria as well as on the heterologous expression of these genes and on the availability of mutants impaired in the accumulation of PHA. In addition, a terminology for the designation of PHAs and of proteins and genes relevant for the metabolism of PHA is suggested.

From genomic libraries of the purple non-sulfur bacteria Rhodospirillum rubrum Ha and Rhodobacter sphaeroides ATCC 17023 in the broad-host range cosmid pVK100, we cloned a 15- and a 14-kbp HindIII restriction fragment, respectively. Each of these fragments restored the ability to accumulate poly(3-hydroxybutyrate) (PHB), in the PHB-negative mutant Alcaligenes eutrophus PHB-4. These hybrid cosmids also complemented PHB-negative mutants derived from wild-type R. rubrum or R. sphaeroides. Both fragments hybridized with the PHB synthase structural gene of A. eutrophus H16 and conferred the ability to express PHB synthase activity. Only the 15-kbp HindIII fragment from R. rubrum conferred on the mutant PHB-4 the ability to form large PHB granules (length up to 3.5 microns).

Abstract— The photophobic response of 34 strains of nonsulfur and sulfur purple bacteria was examined with respect to response‐eliciting light intensities. The bacteria were grown in defined synthetic media or in Winogradsky columns. Two population methods based on Engelmann's light trap were used to determine the discrimination thresholds of the bacteria. A single‐side irradiation method allowed the estimation of approximate values, while the double‐side irradiation method provided more exact values of the discrimination threshold. Sixteen strains belonging to 9 different species exhibited discrimination thresholds between 0.7% and 2.6%. The motility of the other 18 strains proved to be insufficient to measure light sensitivities with the methods used. The effect of various environmental factors on the light sensitivies of Chromatium vinosum D and Rhodospirillum rubrum Ha was examined. The measurements and observations made in this work recommend strains of Rhodospirillum rubrum and Chromatium vinosum as model organisms for further studies.