Bacterial zonation,photosynthesis, and spectral light distribution in hot spring microbial mats of Iceland |
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Authors: | Bo Barker Jørgensen Douglas C. Nelson |
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Affiliation: | (1) Institute of Ecology and Genetics, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark;(2) Department of Bacteriology, University of California, 95616 Davis, California, USA |
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Abstract: | The zonation and structure of phototrophic microbial mats were studied along two thermal gradients in sulfide-rich hot springs of southwest Iceland. The green, filamentous bacteriumChloroflexus and the unicellular, high-temperature form (HTF) ofMastigocladus formed mats growing up to a temperature limit of 62–66°C. The dominant phototrophs wereChloroflexus sp.,Mastigocladus laminosus, andPhormidium laminosum, respectively, at the three temperature intervals: >60°C, 60°C to 55–50°C, and <55–50°C. AChloroflexus mat growing at 60°C under 60M H2S was anoxic in the light with the exception of a 0.5 mm thick band of HTFMastigocladus which produced oxygen. The oxygenic photosynthesis of these H2S-sensitive cyanobacteria was probably dependent on a preceding sulfide depletion by the anoxygenicChloroflexus. Measurements of spectral radiance gradients with a fiberoptic microprobe showed maximum light attenuation by carotenoids and bacteriochlorophyllC. AM. laminosus mat growing at 52°C was oxic throughout and showed maximum light attenuation by carotenoids, chlorophyllA, and phycocyanin, but no detectable phycoerythrocyanin absorption. |
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