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Seven different carotenoids with the number of conjugated double bonds (N) from 5 to 11 were incorporated in vitro into carotenoidless complexes LH2 of the sulfur bacterium Allochromatium vinosum strain MSU. The efficiency of their incorporation varied from 4 to 99%. The influence of N in the carotenoid molecules on the energy transfer efficiency from these pigments to bacteriochlorophyll (BChl) in the modified LH2 complexes was studied for the first time. The highest level of energy transfer was recorded for rhodopin (N = 11) and neurosporene (N = 7) (37 and 51%, respectively). In the other carotenoids, this parameter ranged from 11 to 33%. In the LH2 complexes studied, we found no direct correlation between the decrease in N in carotenoids and increase in the energy transfer efficiency from these pigments to BChl. [ABSTRACT FROM AUTHOR]

An alkaliphilic nonsulfur purple bacterial (NPB) strain “Green” was isolated from sediments of the littoral zone of the soda lake (mineralization 22 g/l, pH 9.5) in the Barguzin River valley (Eastern Siberia). The cells of the new isolate are ovoid or polymorphic at latter stages. The photosynthetic membrane structures are of vesicular type. Bacteriochlorophyll a and carotenoids of both spheroidene and spirilloxanthin type are the photosynthetic pigments. Two light-harvesting systems (LH1 and LH2) are present. The new isolate is a photoheterotroph and a facultative aerobe. It grows well in the dark on organic substrates; anaerobic phototrophic growth is poor. The isolate is alkaliphilic with pH optimum of 8.5–9.5. The most abundant cell growth occurred at 5–40 g/l NaCl (optimum at 10 g/l) and 30 °C. The DNA G+C base content was 69.9 mol %. Analysis of 16S rRNA gene sequences revealed a 10% difference with the most closely related NPB ( Rhodobacter species). Rubrimonas cliftoensis, a bacteriochlorophyll a-containing bacterium, is the closest relative (93.3% similarity). It is proposed that strain “Green” should be placed in the new genus and new species Rubribacterium polymorphum gen. nov., sp. nov. GenBank accession number: 16S rRNA-EU857676. [ABSTRACT FROM AUTHOR]

The article presents research on the carotenoid-photosensitized oxidation of bacteriochlorophyll (BChl) dimers in complexes B800-850 that are light-harvesting in "Allochromatium minutissimum" cells. The study examined the photooxidation of bacteriochlorophyll dimers that are sensitized by light absorbed by carotenoids in Alc. minutissimum cells. Results of the study include the high resistance of BChl to white light in pigment-protein complexes in which carotenoid synthesis is inhibited.

A new nonmotile purple sulfur bacterium (strain M9) was isolated from the steppe soda lake Lake Dzun Uldziin Nur (pH 9.4; mineralization, 3.3%) situated in southeastern Mongolia. Individual cells appear as vibrios 0.3–0.5 × 0.7–1 μm in size. The dividing cells often do not separate from each other, forming an almost closed ring. The internal photosynthetic membranes are represented by concentric lamellae lining the cell wall. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. The main carotenoid (>96%) is spirilloxanthin. Two typical light-harvesting complexes (LH1 and LH2) are present in the membranes in a 1 : 1 ratio. The bacterium is an anaerobe and facultative photoorganoheterotroph. Photolithoautotrophic growth on sulfide is scarce. Thiosulfate is utilized as an electron donor only in the presence of organic matter. Globules of elemental sulfur are formed as an intermediary product of sulfide and thiosulfate oxidation and are deposited outside the cells. The end product of oxidation is sulfate. In the presence of sulfide and carbonates, acetate, lactate, malate, pyruvate, propionate, succinate, and fumarate are used as additional sources of carbon in anoxygenic photosynthesis. Vitamins are not required. The bacterium is an alkaliphile, the pH optimum is at 8.3–9.1, the pH range is 7.6–10.1. The optimum NaCl concentration in the medium is 1 to 7%; the range is 0.5 to 0.9%. The optimum carbonate content in the medium is 2%; the range is 1 to 10%. The best growth occurs at 30–35°C. The DNA G+C content is 57.5 mol %. According to the results of analysis of the 16S rRNA gene sequences, the new isolate M9 belongs to the phylogenetic cluster containing representatives of the family Ectothiorhodospiraceae within the class “Gammaproteobacteria.” In this class, the new isolate forms a new branch, which occupies an intermediate position between the representatives of the genera Ectothiorhodospira and Thiorhodospira. Based on the phenotypic and genetic characteristics, the new purple sulfur bacterium was assigned to a new species of a new genus of the family Ectothiorhodospiraceae, Ectothiorhodosinus mongolicum gen. nov., sp. nov. [ABSTRACT FROM AUTHOR]

Presents a study on some spectral characteristics of pigment-protein complexes and their interaction in membranes of Thiorhodospira (Trs.) sibirica. Bifunctional agent used to study the processes of interaction between the pigment-protein complexes in carotenoid-containing and carotenoidless membranes of Trs. sibirica bacterium; Manner in which bacterial cells were disintegrated; Method used to assay the carotenoids; Spectral features of the absorption spectrum of the Trs. sibirica photosynthetic membranes.