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Phototrophic purple sulfur bacteria as heat engines in the South Andros Black Hole

2007; Springer Science+Business Media; Volume: 95; Issue: 2-3 Linguagem: Inglês

10.1007/s11120-007-9246-1

1573-5079

R. A. Herbert, Andrew Gall, Takashi Maoka, Richard J. Cogdell, Bruno Robert, Shinichi Takaichi, Stephanie Schwabe,

Algal biology and biofuel production

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.