Microbial communities structure of the Japan Trench cold-seeps determined by lipid analysis

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2005-01-01
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Chan, Wai
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Abstract

Seafloor cold seeps support some of the most prolific and diverse ecosystems on Earth. A multitude of microbial habitats are associated with cold seeps. The seeping fluids are enriched in reduced chemical species such as sulfide and methane. These reduced species are utilized by microorganisms to gain energy from the reduction of sulfate and oxidation of methane, or the so-called anaerobic oxidation of methane (AOM). The Japan Trench is the deepest seafloor cold seeps found on earth and characterized by abundant chemosynthesis-based communities associated with the cold seeps. Chemosynthetic communities of Maorithyas hadalis and Calyptogena phaseoliformis have been discovered at depth of over 7,000 m. In this project, four sediments samples from chemosynthetic communities dominated by M. hadalis and C. phaseoliformis and two clam tissue (leg and gill) samples of M hadalis were collected. To obtain quantitative information of the Japan Trench cold-seeps, lipid analysis was used to determine the sedimentary microbial community structure of both communities, and to identify the symbionts living inside the Maorithyas hadalis gill tissue. Phospholipid fatty acids, hopanoids, glycolipid fatty acids, sterols and n-alkanes were isolated from the samples and analyzed using gas chromatography/mass Spectrometry (GC/MS). The total microbial biomass were estimated to be 5.71 x 10⁸ and 4.58 x 10⁸ cells (g dry wt)⁻¹ for the Maorithyas and Calyptogena sediments, respectively. The microbial biomarker assemblages of the sediments indicate similar complex consortia of microorganisms were present in both communities, including sulfate-reducing and sulfur-oxidizing bacteria. The lipid profiles isolated from the M hadalis gills contained large amount of monounsaturated (C16:1, C18:1 and C20:1), terminal-branched (iC15:0, aC15:0, iC17:0), cyclopropane (C17: 0cy) and polyunsaturated fatty acids (C18:2, C20:4, C20:5 and C22:2), suggesting the presence of sulfur-oxidizers including Thiomicrospira species as symbiotic bacteria. From these results, I propose a model of the coupled carbon and sulfur cycling within the chemosynthetic communities in the Japan Trench cold-seeps.

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Sat Jan 01 00:00:00 UTC 2005