Studies on the comparative physiology of the aerobic photosynthetic bacteria

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1. Taxonomy, distribution and characteristics: The aerobic photosynthetic bacteria identified so far were facultative methyloprophs and marine bacteria. The genus, Protomonas,for the former and the genus, Erythrobacter, for the latter were proposed. Many unidentified marine bacteria suggested to be the aerobic photosynthetic bacteria.2. Biochemical characteristics: (1) All of the aerobic photosynthetic bacteria tested contained bacteriochlorophyll a and photochemical reaction center and the light-harvesting bacteriochlorophyll protein complexes, all similar to those of common photosynthetic bacteria. In most of the aerobic photosynthetic bacteria unbound carotenoid pigments, which did not transfer light energy to bacteriochlorophyll, were found and these pigments were structurally different from those in the common photosynthetic bacteria. Amino acid sequence of one of the soluble cytochromes in E. OCh 114 had the high homology to that of cytochrome c_2. Cytochrome oxidase (aa_3) in E. … More longus, which consisted of one subunit, was purified. (2) -Aminolevulinic acid synthase and porphobilinogen synthase were purified from Protaminobacter ruber NR-1 and E. OCh 114, respectively. This suggested that biosynthetic pathway of bacteriochlorophyll in the aerobic photosynthetic bacteria was similar to that of the common photosynthetic bacteria.3. Physiological characteristics: (1) Photosynthesis of E. OCh 114 did not take place under anaerobic conditions. In the presence of "auxiliary oxidants" such as trimethylamine-N-oxide, nitrate and nitrite, the photosynthesis was restored ubder anaerobic conditions. These results suggested that the regulation of the redox balance in the electron transport system, especially of photosynthesis, did not operate under anaerobic conditions. (2) E. OCh 114 grew anaerobically in the presence of these auxiliary oxidants. In the presence of nitrate, nitrous oxide was evolved during anaerobic growth, suggesting that this bacterium had the denitrification activity. There was no bacteriochlorophyll formation during the anaerobic growth in both the light and dark. The regulation by molecular oxygen on bacteriochlorophyll formation may be different from that in the case of the common photosynthetic bacteria. Less