Reconstruction of Bacteriochlorophyll Biosynthesis Pathways in the Filamentous Anoxygenic Phototrophic Bacterium Oscillochloris trichoides DG-6 and Evolution of Anoxygenic Phototrophs of the Order Chloroflexalesстатья
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Дата последнего поиска статьи во внешних источниках: 8 ноября 2016 г.
Аннотация:It is commonly accepted that green filamentous anoxygenic phototrophic (FAP) bacteria are the most ancient representatives of phototrophic microorganisms. Modern FAP belonging to the order Chloroflexales are divided onto two suborders - Chloroflexineae and Roseiflexineae. Representatives of Roseiflexineae lack chlorosomes and synthesize bacteriochlorophyll a, whereas those of Chloroflexineae synthesize bacteriochlorophylls a and c and utilize chlorosomes for light harvesting. Involving a small number of species, FAP are quite diverse in their physiology. This bacterial group includes autotrophs and heterotrophs, thermophiles and mesophiles, aerobes and anaerobes, and they occupy both freshwater and halophilic environments. The anaerobic mesophilic autotroph Oscillochloris trichoides DG-6 is still not well studied in its physiology, and its evolutionary origin remains unclear. The goals of this study included identification of the reaction center type of Osc trichoides DG-6, reconstruction of its bacteriochlorophyll biosynthesis pathways, and determination of its evolutionary relationships with other FAP. According to data of enzymatic and genomic analysis, the presence of RCII in Osc trichoides DG-6 was demonstrated and the complete gene set involved in biosynthesis of bacteriochlorophylls a and c was established. We found that the bacteriochlorophyll gene sets differed between aerobic and anaerobic FAP. The aerobic FAP genomes code oxygen-dependent AcsF cyclases, but lack the bchQ/bchR genes, which have been associated with adaptation to low light conditions in the anaerobic FAP. A scenario of evolution of FAP belonging to the order Chloroflexales is proposed.