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Photosynth Res DOI 10.1007/s11120-007-9246-1

REGULAR PAPER

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

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

Received: 6 September 2007 / Accepted: 7 September 2007

  • Springer Science+Business Media B.V. 2007

Abstract

Photosynthetic organisms normally endeavor to

optimize the efficiency of their light-harvesting apparatus. However, here we describe two bacterial isolates belonging

to the strate

genera Allochromatium and Thiocapsa that demon- a novel adaptation by optimizing their external

growth ciency.

conditions at the expense of photosynthetic effi- In the South Andros Black Hole, Bahamas, a dense

Electronic supplementary material The online version of this article (doi:10.1007/s11120-007-9246-1) contains supplementary material, which is available to authorized users.

R. A. Herbert (&) Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK e-mail: r.a.herbert@dundee.ac.uk

l-m thick layer of these anoxygenic purple sulfur bacteria is present at a depth of 17.8 m. In this layer the water tem- perature increases sharply to 36C 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 spi- rilloxanthin-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.

Keywords

Anoxygenic

purple sulfur bacteria

A. Gall B. Robert Institut de Biologie et Technologies de Saclay, Commissariat `a l’Energie Atomique, Gif sur Yvette 91191, France

Allochromatium Thiocapsa South Andros Black Hole

Carotenoid Spirilloxanthin

Energy-transfer

A. Gall e-mail: andrew.gall@cea.f

Introduction

T. Maoka Research Institute for Production Development, Shinogamo-morimoto-cho, Sakyou-ku, Kyoto 606-0805 Japan

RichardJ. Cogdell Institute of Biomedical and Life Sciences, University of Glasgow, Biomedical Research Building, Glasgow G12 8TA, UK

S. Takaichi Biological Laboratory, Nippon Medical School, Nakahara, Kawasaki 211-0063, Japan

S. Schwabe International Blue Holes Foundation, 5 Longitude Lane, Charleston, SC 29401, USA

Heat exchange between living cells and their surroundings is a universal phenomenon. It is, however unusual, in natural environments, for microorganisms to significantly raise the temperature of their immediate surroundings since, high cell densities are rarely achieved and metabolic heat generated is usually rapidly dissipated. Notable exceptions to this general rule, however, can be found in artificial high cell density closed systems, such as compost heaps, silage pits, and fermenters (Hunter 1917; Wang et al. 1979; Diaz et al. 1993). In marine environments such as the Baltic, Kahru et al. (1993) using Advanced Very High Resolution Radiometer (AVHRR) satellite images in con- junction with shipboard measurements showed that surface

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