title: Phototrophic purple sulfur bacteria as heat engines in the South Andros Black Hole.
abstract: Photosynthetic organisms normally endeavor to optimize the efficiency of their light-harvesting apparatus. However, here we describe two bacterial isolates belonging to the genera Allochromatium and Thiocapsa that demonstrate a novel adaptation by optimizing their external growth conditions at the expense of photosynthetic efficiency. In the South Andros Black Hole, Bahamas, a dense l-m thick layer of these anoxygenic purple sulfur bacteria is present at a depth of 17.8 m. In this layer the water temperature increases sharply to 36 degrees C as a consequence of the low-energy transfer efficiency of their carotenoids (ca. 30%). These include spirilloxanthin, and related polyene molecules and a novel chiral carotenoid identified as spirilloxanthin-2-ol, not previously reported in purple bacteria. To our knowledge, this study presents the first evidence of such a bacterial mass significantly increasing the ambient water temperature. The transduction of light to heat energy to excess heat may provide these anoxygenic phototropic bacteria with a competitive advantage over non-thermotolerant species, which would account for their predominance within the microbial layer.
authors: Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee, DD1 4HN, UK. r.a.herbert@dundee.ac.uk
authors: Rodney A
authors: RA
authors: Herbert
authors: Andrew
authors: A
authors: Gall
authors: Takashi
authors: T
authors: Maoka
authors: Richard J
authors: RJ
authors: Cogdell
authors: Bruno
authors: B
authors: Robert
authors: Shinichi
authors: S
authors: Takaichi
authors: Stephanie
authors: S
authors: Schwabe
mesh_terms: D002338:Carotenoids / Q000302:isolation & purification; D002841:Chromatiaceae / Q000254:growth & development / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D055537:Light Signal Transduction; D019906:Nuclear Magnetic Resonance, Biomolecular; D010788:Photosynthesis; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D002338:Carotenoids