The protein patterns of intracytoplasmic membranes and reaction center particles isolated from Rhodopseudomonas capsulata

Forty-five years of developmental biology of photosynthetic bacteria

Developmental biology and cell differentiation of photosynthetic prokaryotes are less noticed fields than the showpieces of eukaryotes, e.g. Drosophila melanogaster. The large metabolic versatility of the facultative purple bacteria and their great capability to adapt to different ecological conditions, however, aroused the inquisitiveness to investigate the process of cell differentiation and to use these bacteria as model system to study structure, function and biosynthesis of the photosynthetic apparatus. The great progress in research in this field paved the way to study principal mechanisms of cellular organization and differentiation in these bacteria. In this article, the history of the research on membrane structure and development of anoxygenic photosynthetic prokaryotes during the last 45 years is described. A personal account of how I entered the field through research on the phototaxis of cyanobacteria is given. Intracytoplasmic membranes (ICM) were detected by electron microscopy in cyanobacteria and in purple non-sulfur bacteria. The formation of ICM by invagination of the cytoplasmic membrane in purple bacteria was observed for the first time. Investigations on the effect of changes in oxygen tension and light intensity on the formation of pigments and intracytoplasmic membranes followed. The isolation, purification, and analysis of light-harvesting complexes and of pigment-binding proteins was the next step of our research. Lipopolysaccharides and peptidoglycans were detected and analyzed in the outer membrane of photosynthetic bacteria. Functional membrane differentiation includes variations in the rates of photophosphorylation and electron transport. Molecular genetic approaches have initiated the investigation of transcriptional regulation and the analysis of correlation between pigment and protein synthesis. Molecular analysis of assembly of light-harvesting complexes and membrane differentiation are the present aspects of our research. Cell differentiation has been considered under evolutionary view.

Construction of a gene bank of Rhodopseudomonas capsulata using a broad host range DNA cloning system

A gene bank of the phototrophic bacterium Rhodopseudomonas capsulata was constructed using the binary plasmid system pRK290/pRK2013. Fragments of about 20 kb of chromosomal DNA of R. capsulata strain 37b4 were inserted into the cloning vector pRK290. The hybrid plasmids of the gene bank, maintained in Escherichia coli HB101 were transferred by conjugation to R. capsulata strains defective in the photosynthetic apparatus with frequencies of 5 X 10(-4) to 5 X 10(-2). Phototrophically growing transconjugants occurred with frequencies of 5 X 10(-7) to 5 X 10(-6). Recombination between the hybrid plasmids and the R. capsulata chromosome was shown. The hybrid plasmid pRCF1002, carrying a 25 kb insert of R. capsulata wild type DNA, was isolated from one E. coli clone of the gene bank. It reconstituted some bacteriochlorophyll- and photosynthetic negative mutants to phototrophic growth.

Modifiable chromatophore proteins in photosynthetic bacteria

The chromatophores of Chromatium vinosum, as well as six other photosynthetic bacteria, contained two or more proteins which were insoluble when heated in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (beta-ME). When the chromatophores were dissolved at room temperature in SDS-beta-ME, these proteins were present in the SDS-polyacrylamide gel electrophoresis profiles, but when the samples were dissolved at 100 degrees C, they were absent or considerably diminished. When one-dimensional gels of chromatophores solubilized at room temperature were soaked in the SDS-beta-ME solution and heated to 100 degrees C and the gels were run in a second dimension, the proteins became immobilized in the original first-dimension gel, where they could be detected by staining. The two major proteins so affected in C. vinosum had apparent molecular weights of 28,000 and 21,000. The chromatophores of several other photosynthetic bacteria also contained predominant proteins between 30,000 and 19,000 molecular weight, which became insoluble when heated in the presence of SDS and beta-ME. In at least two of the species examined, these appeared to be reaction center proteins. The conditions causing the proteins to become insoluble were complex and involved temperature, SDS concentration, and the presence of sulfhydryl reagents. The chromatophores of four of the Chromatiaceae species and two strains of one of the Rhodospirillaceae species examined had a protein-pigment complex that was visible in SDS-polyacrylamide gel profiles of samples dissolved at room temperature but was absent in samples dissolved at 100 degrees C.

Isolation and characterization of membranes from a hydrocarbon-oxidizing Acinetobacter sp

Membranes were isolated and purified from nutrient broth-yeast extract- and hexadecane-grown cells of Acinetobacter sp. strain HO1-N. Two membrane fractions were isolated from nutrient broth-yeast extract-grown cells, the cytoplasmic membrane and the outer membrane. In addition to these two membrane fractions, a unique membrane fraction was isolated from hexadecane-grown cells (band 1) and characterized as a lipid-rich, low-density membrane containing high concentrations of hexadecane. The outer membrane preparations of Acinetobacter, obtained from nutrient broth-yeast extract- and hexadecane-grown cells, exhibited a low ratio of lipid phosphorus to protein and contained phospholipase activity and 2-keto-3-deoxyoctulosonic acid. Phosphatidic acid cytidyltransferase, adenosine triphosphatase, and reduced nicotinamide adenine dinucleotide oxidase were recovered almost exclusively in the cytoplasmic membrane fractions. The cytoplasmic membrane fractions contained 20 to 25 polypeptide species on sodium dodecyl sulfate-polyacrylamide gels, and the outer membrane fractions contained 15 to 20 polypeptide species. A major polypeptide species with an apparent molecular weight of approximately 42,000 to 44,000 was found for all outer membrane fractions. The buoyant densities of the cytoplasmic membrane fractions and the outer membrane fractions were closely similar, necessitating their separation by differential centrifugation. Band 1 of hexadecane-grown cells had a ratio of lipid phosphorus to protein that was almost twice that of cytoplasmic membrane and a correspondingly low buoyant density (1.086 g/cm3). Enzyme activities associated with band 1 were identical to those associated with the cytoplasmic membrane. The electrophoretic banding pattern of band 1 was essentially identical to the banding pattern of the cytoplasmic membrane. The phospholipid and neutral lipid compositions of the isolated membrane fractions were determined as qualitatively similar, with significant quantitative differences. The ultrastructure characteristics of the respective membrane fractions were examined by the negative-stain technique.

Control of composition and activity of the photosynthetic apparatus of Rhodopseudomonas capsulata grown in ammonium-limited continuous culture

Rhodopseudomonas capsulata was grown either phototropically in the light or chemotrophically in the dark at oxygen tensions of 5 mm and 3 mm Hg in ammonium-limited continuous culture. During growth limitation bacteriochlorophyll content of cells and membranes varied dependent on growth rate drastically in chemotrophic cultures. Concomittantly, the ratio of membrane protein to total protein varied in the range of 30-41%. This dependence of membrane differentiation on growth rate was less evident in phototrophically grown cells. The incorporation of the bulk of bacteriochlorophyll was shown to be quantitatively correlated to the incorporation of 1-3 low molecular weight proteins with molecular weights in the range of 14 to less than 10 k daltons. Supported by similar findings of other authors it is proposed, that these proteins are to be attributed to the species of antenna bacteriochlorophyll and represent components of the photosynthetic apparatus. With decreasing growth rates the size of the photosynthetic unit with respect to the population of bacteriochlorophyll- and protein molecules was reduced subsequent to a reduction in the rate of incorporation of antenna-bacteriochlorophyll and the low molecular weight proteins, the reaction-center bacteriochlorophyll content of the membranes remaining constant. A parallel decrease in potential phosphorylating capacity was observed. It is concluded, that under these conditions, primary photochemical reactions in the reaction center were not the rate-limiting step in photophosphorylation. The interaction of growth limitation by an anabolic precursor (NH+4) and control of membrane differentiation by light intensity or oxygen tension is discussed.

Photochemical reaction centers from Rhodopseudomonas capsulata

A photochemically active bacteriochlorophyll-protein complex (reaction center) has been isolated from the carotenoidless mutant A1a+ of Rhodopseudomonas capsulata by treatment of membranes with lauryl dimethyl amine oxide. Three proteins with molecular weights of 20,500, 24,000 and 28,000 (molar ratio 1:1:1) were detected in the reaction center preparations. After mild treatment of intracytoplasmic membranes with Na-dodecyl sulfate (0.5%, 30 degrees C, 1 min) succeeded by polyacrylamide gel electrophoresis two pigmented bands were obtained. Material of one fraction could be bleached reversibly by actinic light and contained two proteins with molecular weights of 20,500 and 24000. The second band is photochemically inactive.

Formation of reaction centers and light-harvesting bacteriochlorophyll-protein complexes in Rhodopseudomonas capsulata

Formation of the photosynthetic apparatus was induced in aerobically grown dark cultures of Rhodopseudomonas capsulata by lowering of the oxygen tension. Besides the wild type strain the carotenoid-less mutant strain A1a+ was investigated. Both strains exhibited initially a decrease of the molar ratio of total bacteriochlorophyll (Bchl) to reaction center (RC) Bchl, followed by an increase. Synthesis of RC-Bchl preceded the synthesis of light-harvesting (LH) Bchl. Activities of photophosphorylation in membrane preparations, isolated from cultures after different periods of incubation at low aeration, decreased on the basis of total Bchl from about 9 to 2 mumole ATP/mumole total Bchl-min, whereas the rate on the basis of RC-Bchl remained constant (about 500 mumole ATP/mumole RC-Bchl-min). Under the same conditions the membrane proteins were labelled with U-14C-protein hydrolysate. Corresponding to RC-Bchl the synthesis of RC-proteins dominated during the first 30 min of incubation at PO2 below 3 mm Hg. After 45-60 min of membrane formation at low aeration the synthesis of LH-complex proteins exceeded the synthesis of RC proteins. The correlations between protein and Bchl synthesis in the sequential formation of RC- and LH-complexes are discussed.

On reconstitution of bacterial photophosphorylation in vitro

Membranes active in oxidative phosphorylation but inactive in photophosphorylation were isolated from a carotenoid-less and bacteriochlorophyll-less mutant strain of Rhodopseudomonas capsulata. These membranes were uncoupled and recombined with coupling factor from the same strain and with reaction centers from a photosynthetically active revertant strain. The reconstituted system was able to form ATP from ADP and inorganic phosphate under anaerobic conditions in the light. Rates of 2 nmoles of ATP formed per min per mug of bacteriochlorophyll were obtained. A high incorporation of (32)P from inorganic phosphate into ADP in the light as well as in the dark was observed, the activity of which was associated with coupling factor. This incorporation occurs both aerobically and anaerobically and appears to be independent of photophosphorylation.