Phototrophic Nonsulfur Bacterium Research Articles

Aerobic anoxygenic phototrophic bacteria.

The aerobic anoxygenic phototrophic bacteria are a relatively recently discovered bacterial group. Although taxonomically and phylogenetically heterogeneous, these bacteria share the following distinguishing features: the presence of bacteriochlorophyll a incorporated into reaction center and light-harvesting complexes, low levels of the photosynthetic unit in cells, an abundance of carotenoids, a strong inhibition by light of bacteriochlorophyll synthesis, and the inability to grow photosynthetically under anaerobic conditions. Aerobic anoxygenic phototrophic bacteria are classified in two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Erythromonas, Porphyrobacter, Roseococcus, and Sandaracinobacter) genera, which phylogenetically belong to the alpha-1, alpha-3, and alpha-4 subclasses of the class Proteobacteria. Despite this phylogenetic information, the evolution and ancestry of their photosynthetic properties are unclear. We discuss several current proposals for the evolutionary origin of aerobic phototrophic bacteria. The closest phylogenetic relatives of aerobic phototrophic bacteria include facultatively anaerobic purple nonsulfur phototrophic bacteria. Since these two bacterial groups share many properties, yet have significant differences, we compare and contrast their physiology, with an emphasis on morphology and photosynthetic and other metabolic processes.

Purification and characterization of a catalase from the nonsulfur phototrophic bacterium Rhodobacter sphaeroides ATH 2.4.1 and its role in the oxidative stress response.

When challenged with reactive oxidants, the nonsulfur phototrophic bacterium Rhodobacter sphaeroides ATH 2.4.1 exhibited an oxidative stress response during both phototrophic and chemotrophic growth. Upon preincubation with 100 microM H2O2, catalase activity increased fivefold. Catalase was also induced by other forms of oxidative stress, heat-shock, ethanol treatment, and stationary-phase conditions. Only one band of catalase activity was detected after native and denaturing PAGE. The enzyme was purified 304-fold with a yield of 7%. The purified enzyme displayed a heterodimeric structure with subunits of 75 and 68 kDa, corresponding to a molecular mass of approximately 150 kDa for the native enzyme. The subunits had almost identical amino-terminal peptide sequences, sharing substantial similarity with other bacterial catalases. The enzyme exhibited an apparent Km of 40 mM and a Vmax of 285,000 U (mg protein)-1. Spectroscopic analysis indicated the presence of protoheme IX. The heme content calculated from pyridine hemochrome spectra was 0.43 mol per mol of enzyme. The enzyme had a broad pH optimum and was inhibited by cyanide, azide, hydroxylamine, 2-mercaptoethanol, and sodium dithionite. These data indicate that this catalase belongs to the class of monofunctional catalases.

Photobiotransformation of indole to its value-added derivatives by Rhodobacter sphaeroides OU5

A purple non-sulfur anoxygenic phototrophic bacterium, Rhodobacter sphaeroides OU5 was able to photobiotransform indole in the presence of various organic substrates to its value-added derivatives tryptophan, tryptamine, indole lactic acid and indigo, which are of high commercial value. The product formed varied with the precursors provided in the medium.

Crystallization and preliminary X-ray diffraction analysis of cytochrome c' from Rubrivivax gelatinosus at 1.3 A resolution.

Cytochrome c' from the purple non-sulfur phototrophic bacterium Rubrivivax gelatinosus has been crystallized by vapour diffusion at pH 5, 6.3 and 8, in sodium acetate, sodium citrate, and Tris-HCl buffers, respectively. Crystals grown at pH 5 and 6.3 diffract, respectively, to 2.0 A (298 K) and 1.4 A (100 K) using synchrotron radiation. Data up to 1.3 A resolution with 99.8% completeness were collected at 100 K on a crystal grown at pH 8. The space group is P3121 or P3221, and the unit-cell parameters are a = b = 69.63, c = 123.63 A.

Cloning of dnaK and dnaJ homologous genes from a purple non-sulfur bacterium Rhodopseudomonas species

The dnaK and dnaJ genes were isolated as a cluster from a purple non-sulfur phototrophic bacterium, Rhodopseudomonas species No. 7 by a polymerase chain reaction (PCR) based method. The deduced products of dnaK (631 amino acids) and dnaJ (379 amino acids) were 67% and 56% identical to the respective Escherichia coli gene products. The functions of DnaK and DnaJ could be confirmed by complementation of the respective E. coli mutants.

Dimethylsulfide:acceptor oxidoreductase from Rhodobacter sulfidophilus. The purified enzyme contains b-type haem and a pterin molybdenum cofactor.

Dimethylsulfide:receptor oxidoreductase was purified from the purple non-sulfur phototrophic bacterium Rhodobacter sulfidophilus. The native form of the enzyme had a molecular mass of 152 kDa and was composed of three distinct subunits of 94, 38 and 32 kDa. Dimethylsulfide:acceptor oxidoreductase did not oxidise other thioethers which were tested. The enzyme was able to reduce a variety of N-oxides using reduced methylviologen as electron donor but it reduced dimethylsulfoxide at a very low rate. The resting form of dimethylsulfide:acceptor oxidoreductase exhibited a spectrum which was characteristic of a reduced cytochrome with absorbance maxima at 562 nm, 533 nm and 428 nm. Pyridine haemochrome analysis established that the cytochrome contained a b-type haem and a content of 0.65 mol protohaem/mol enzyme was determined. After oxidation of the haem with ferricyanide, the absorbance spectrum of the reduced cytochrome was restored by reduction with dimethylsulfide. Metal analysis revealed that dimethylsulfide:acceptor oxidoreductase contained 0.5 mol Mo and 3.5 mol Fe/mol enzyme. Heat treatment of the enzyme released material with fluorescence excitation and emission spectra which were characteristic of form B of the pterin component of the pterin molybdenum cofactor. From this analysis it is concluded that dimethylsulfide:acceptor oxidoreductase is a molybdenum oxotransferase which may also contain a iron-sulfur cluster. It is suggested that the haem and pterin molybdenum cofactor are associated with the 94-kDa subunit.

A new mutation in the pufL gene responsible for the terbutryn resistance phenotype in Rubrivivax gelatinosus

Rubrivivax gelatinosus is a facultative phototrophic non-sulfur bacterium belonging to the β subclass of the purple bacteria. A terbutryn-resistant mutant of R. gelatinosus has been isolated and characterized. Increased resistance levels to terbutryn (300-fold), atrazine (6-fold) and o-phenanthroline (3-fold) were observed for the mutant compared with wild type. Sequence analysis of the mutant revealed a new mutation in the pufL gene coding for the L subunit of the reaction centre (RC) at codon 192 leading to an amino-acid substitution from Gly in the wild type to Asp in the mutant. This substitution is located in the D helix of the L subunit, suggesting an interaction between terbutryn and this part of the polypeptide in the RC of R. gelatinosus. This is the first report of a mutation leading to herbicide resistance and affecting the D helix in purple bacteria. Furthermore R. gelatinosus wild type is highly sensitive to o-phenanthroline compared with other purple bacteria ( Rhodobacter capsulatus and Rhodobacter sphaeroides). Sequence comparison of the L subunit from six purple bacteria in which o-phenanthroline sensitivity was measured suggests that Ser L226 might be responsible for this phenotype.

A new genus of marine budding phototrophic bacteria, Rhodobium gen. nov., which includes Rhodobium orientis sp. nov. and Rhodobium marinum comb. nov.

Strains of a previously undescribed species of purple nonsulfur phototrophic bacteria were isolated from coastal seawater in Japan. These new isolates were gram-negative, motile, budding rods that contained lamellar intracytoplasmic membranes and produced pink to red cultures. Cell extracts of photosynthetic cultures exhibited absorption maxima at 377, 468, 500, 530, 591, 802, and 870 nm, indicating that bacterio-chlorophyll a and carotenoids of the spirilloxanthin series were present. The new isolates were halophilic, facultatively aerobic photoheterotrophs that grew anaerobically in the light or aerobically in the dark. Maximum growth occurred in the presence of 4 to 5% NaCl. Anaerobic growth in the dark with nitrate as a terminal electron acceptor also occurred. Various organic compounds were used as photosynthetic electron donors and carbon sources. Sulfate was used as a sulfur source. Both menaquinone 10 and ubiquinone 10 were produced; these quinones were the major quinones. A phylogenetic analysis based on 16S rRNA gene sequences revealed that strain MB312T (T = type strain), a representative of the new phototrophs, was a member of a lineage that was distinct from members of the genus Rhodopseudomonas; Rhodopseudomonas marina was the closest relative. On the basis of the data described above, we propose the name Rhodobium orientis gen. nov., sp. nov. for the new isolates. We also propose that Rhodopseudomonas marina Imhoff 1983 should be transferred to the genus Rhodobium as Rhodobium marinum comb. nov.

Photosynthetic electron transport and anaerobic metabolism in purple non-sulfur phototrophic bacteria

Purple non-sulfur phototrophic bacteria, exemplified by Rhodobacter capsulatus and Rhodobacter sphaeroides, exhibit a remarkable versatility in their anaerobic metabolism. In these bacteria the photosynthetic apparatus, enzymes involved in CO2 fixation and pathways of anaerobic respiration are all induced upon a reduction in oxygen tension. Recently, there have been significant advances in the understanding of molecular properties of the photosynthetic apparatus and the control of the expression of genes involved in photosynthesis and CO2 fixation. In addition, anaerobic respiratory pathways have been characterised and their interaction with photosynthetic electron transport has been described. This review will survey these advances and will discuss the ways in which photosynthetic electron transport and oxidation-reduction processes are integrated during photoautotrophic and photoheterotrophic growth.

Phototrophic bacteria produce volatile, methylated sulfur and selenium compounds

Abstract Species of phototrophic non-sulfur bacteria produce methylated sulfur compounds, such as dimethylsulfide and dimethyldisulfide. In the presence of selenium oxyanions, analogous organicselenium compounds are formed. These findings suggest that this group of bacteria contribute to the volatilization and biogechemical cycling of sulfur and selenium.

Photosynthesis gene superoperons in purple nonsulfur bacteria: the tip of the iceberg?

The purple, nonsulfur phototrophic bacterium Rhodobacter capsulatus has recently been found to contain several pigment biosynthetic operons that exhibit marked transcription read through into downstream operons that encode polypeptide components of photosynthetic pigment-protein complexes. This phenomenon has been found to be phenotypically significant for adaptation to changes in environmental conditions, and the term superoperon has been proposed to describe this sort of coupled transcriptional arrangement. We summarize the data that led to recognition of this novel transcriptional arrangement and suggest that superoperons might be more prevalent in prokaryotes than has heretofore been recognized. Key words: superoperons, overlapping transcription units, photosynthesis genes.

Purification and properties of L-alanine dehydrogenase of the phototrophic bacterium Rhodobacter capsulatus E1F1.

In the phototrophic nonsulfur bacterium Rhodobacter capsulatus E1F1, L-alanine dehydrogenase aminating activity functions as an alternative route for ammonia assimilation when glutamine synthetase is inactivated. L-Alanine dehydrogenase deaminating activity participates in the supply of organic carbon to cells growing on L-alanine as the sole carbon source. L-Alanine dehydrogenase is induced in cells growing on pyruvate plus nitrate, pyruvate plus ammonia, or L-alanine under both light-anaerobic and dark-heterotrophic conditions. The enzyme has been purified to electrophoretic and immunological homogeneity by using affinity chromatography with Red-120 agarose. The native enzyme was an oligomeric protein of 246 kilodaltons (kDa) which consisted of six identical subunits of 42 kDa each, had a Stokes' radius of 5.8 nm, an s20.w of 10.1 S, a D20,w of 4.25 x 10(-11) m2 s-1, and a frictional quotient of 1.35. The aminating activity was absolutely specific for NADPH, whereas deaminating activity was strictly NAD dependent, with apparent Kms of 0.25 (NADPH), 0.15 (NAD+), 1.25 (L-alanine), 0.13 (pyruvate), and 16 (ammonium) mM. The enzyme was inhibited in vitro by pyruvate or L-alanine and had two sulfhydryl groups per subunit which were essential for both aminating and deaminating activities.

Bicarbonate-stimulated dark fermentative growth of a phototrophic purple nonsulfur bacterium

A phototrophic nonsulfur bacterium, strain FR2, was capable of dark fermentative growth on fructose plus bicarbonate with a doubling time of 4 h. Formate, acetate, succinate, and lactate were formed as major fermentation products. A fumarate reduction system might function to maintain redox balance during fermentative growth of this bacterium.

ELISA analyses of malate dehydrogenases from nonsulfur purple phototrophic bacteria

An enzyme-linked immunosorbent assay using F(ab′)2 fragments of IgG immobilized on a solid surface was used to quantitatively compare the immunological cross-reactivities of the enzyme malate dehydrogenase from purple phototrophic bacteria. The method was found to be reproducible, reliable, and valid for comparative immunological studies of bacterial enzymes. Antisera prepared against purified Rhodobacter capsulatus malate dehydrogenase cross-reacted strongly with the homologous antigen and with that from the related species, R. sphaeroides. Significantly lower cross-reactivities were observed against Rhodospirillum species. Antisera prepared to Rhodospillum rubrum malate dehydrogenase gave just the opposite results. Neither antiserum cross-reacted with malate dehydrogenase from Rhodocyclus species. The taxonomic/phylogenetic conclusions drawn from immunological analyses of phototrophic bacterial malate dehydrogenases were consistent with the grouping of these organisms by 16S ribosomal RNA sequence analyses and with the biochemical properties of their purified malate dehydrogenases. This ELISA method should be applicable for immunological comparisons of enzymes in crude cell extracts and for systematic studies of various bacterial groups.

Quinone systems and cellular fatty acid composition in species of Rhodospirillaceae genera.

Forty nine strains of 12 species of purple nonsulfur phototrophic bacteria (Rhodospirillaceae) and one strain of facultatively methylotrophic bacteria, Protomonas extorquens were investigated with regard to their quinone systems and cellular fatty acid composition. These bacteria had the ubiquinone systems. Some strains had in addition a small amount of menaquinone system, which had the same isoprenoid chain length as the major ubiquinones. The strains in the genera Rhodobacter, Rhodomicrobium, Rhodospirillum, Rhodopseudomonas except for Rhodopseudomonas viridis, and Protomonas extorquens had Q-10 as a major component. Out of the above mentioned strains, the strains of Rhodopseudomonas acidophila also had MK-10 concurrently. The strains of Rhodopila globiformis and Rhodopseudomonas viridis had Q-9 and MK-9. Most of the Rhodocyclus gelatinosus strains had Q-8 and MK-8. The strains of Rhodocyclus gelatinosus contained large amounts of C16:0 acid and C16:1 acid. The strains in the genera Rhodopseudomonas except for Rhodopseudomonas acidophila, Rhodomicrobium, Rhodobacter, and Rhodopila, and in Protomonas extorquens, contained a large amount of C18:1 acid. The strains of Rhodospirillum rubrum, and Rhodopseudomonas acidophila contained large amounts of C16:0 acid, C16:1 acid, and C18:1 acid. Based on these results along with information on other taxonomic properties such as morphology and phylogeny, the relationship of the facultatively methylotrophic bacterium Protomonas extorquens to the species of Rhodospirillaceae genera is discussed.