A purple sulfur bacterium from a high-altitude lake in the Colombian Andes

As a systematic survey of lakes in Colombian Andes, we collected water samples from the Cumbal lake, located at the Western Cordillera at an elevation of 3424 m and recorded simultaneous basic field measurements of water temperature, pH, nutrient and oxygen. Microscopic examination of water drawn from the deeper layers revealed the presence of phototrophic bacteria. From the water samples collected at 18 m depth, a purple sulfur bacterium (strain Bk18) was isolated. Light microscopy revealed spherical cells with intracellular sulfur granules, which are characteristic of the Chromatiaceae. Analysis of the photosynthetic pigments showed the presence of bacteriochlorophyll a with absorption peaks at 373, 800, 853 and 895 nm, respectively. The presence of normal spirilloxanthin carotenoid series was also detected. Gas-chromatography analysis revealed that the following major fatty acids were present: C18:1 (47.58%), C16:1 (27.67%), and C16:0 (12.41%), while the minor fatty acids included C12:0, C13:0, C14:0, C17:0, aC17:0 and C20:1. The morphological and chemotaxonomic properties of the strain Bk18 suggest that this could be placed within the genus Thiocapsa.