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Applied and Environmental Microbiology, December 2008, p. 7546-7551, Vol. 74, No. 24
0099-2240/08/$08.00+0 doi:10.1128/AEM.01186-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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Leibniz Institute for Baltic Sea Research, Section Biology, Seestrasse 15, 18119 Rostock-Warnemünde, Germany,1 Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, 1790 AB Den Burg, The Netherlands2
Received 28 May 2008/ Accepted 15 October 2008
Recent studies have indicated that chemoautotrophic Epsilonproteobacteria might play an important role, especially as anaerobic or microaerophilic dark CO2-fixing organisms, in marine pelagic redoxclines. However, knowledge of their distribution and abundance as actively CO2-fixing microorganisms in pelagic redoxclines is still deficient. We determined the contribution of Epsilonproteobacteria to dark CO2 fixation in the sulfidic areas of central Baltic Sea and Black Sea redoxclines by combining catalyzed reporter deposition-fluorescence in situ hybridization with microautoradiography using [14C]bicarbonate and compared it to the total prokaryotic chemoautotrophic activity. In absolute numbers, up to 3 x 105 14CO2-fixing prokaryotic cells ml–1 were enumerated in the redoxcline of the central Baltic Sea and up to 9 x 104 14CO2-fixing cells ml–1 were enumerated in the Black Sea redoxcline, corresponding to 29% and 12%, respectively, of total cell abundance. 14CO2-incorporating cells belonged exclusively to the domain Bacteria. Among these, members of the Epsilonproteobacteria were approximately 70% of the cells in the central Baltic Sea and up to 100% in the Black Sea. For the Baltic Sea, the Sulfurimonas subgroup GD17, previously assumed to be involved in autotrophic denitrification, was the most dominant CO2-fixing group. In conclusion, Epsilonproteobacteria were found to be mainly responsible for chemoautotrophic activity in the dark CO2 fixation maxima of the Black Sea and central Baltic Sea redoxclines. These Epsilonproteobacteria might be relevant in similar habitats of the world's oceans, where high dark CO2 fixation rates have been measured.
Published ahead of print on 24 October 2008.
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