Phototrophic purple sulfur bacteria as heat engines in the South Andros Black Hole.
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.
Herbert
Rodney A
RA
Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee, DD1 4HN, UK. r.a.herbert@dundee.ac.uk
Gall
Andrew
A
Maoka
Takashi
T
Cogdell
Richard J
RJ
Robert
Bruno
B
Takaichi
Shinichi
S
Schwabe
Stephanie
S
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
D002338:Carotenoids