Abstract
A new species belonging to the photosynthetic bacterial genus Chromatium is described. This new organism differs from all other Chromatium species in its thermophilic character and hot-spring habitat. In addition, the combination of its carotenoid pigments, physiological peculiarities, and deoxyribonucleic acid base composition clearly define this isolate as a new species of photosynthetic purple bacteria. The organism is a rod-shaped, gram-negative bacterium which produces bacteriochlorophyll ap and grows photoautotrophically with sulfide as an electron donor at an optimum temperature of 48 to 50°C. No growth is observed below 34°C or above 57°C. Globules of elemental sulfur are produced from the oxidation of sulfide and are stored intracellularly. Acetate and pyruvate are the only organic compounds that are photoassimilated. The major carotenoids of the new organism are rhodovibrin and spirilloxanthin, and the deoxyribonucleic acid base composition is 61 mol% guanine plus cytosine. Based on these characteristics, I propose a new species, Chromatium tepidum; the specific epithet refers to the moderately thermophilic nature of this hot-spring photosynthetic bacterium.
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