Biogeochemical Activity of Methane-Related Microbial Communities in Bottom Sediments of Cold Seeps of the Laptev Sea.

Bottom sediments at methane discharge sites of the Laptev Sea shelf were investigated. The rates of microbial methanogenesis and methane oxidation were measured, and the communities responsible for these processes were analyzed. Methane content in the sediments varied from 0.9 to 37 µmol CH dm. Methane carbon isotopic composition (δC-CH) varied from -98.9 to -77.6‱, indicating its biogenic origin. The rates of hydrogenotrophic methanogenesis were low (0.4-5.0 nmol dm day). Methane oxidation rates varied from 0.4 to 1.2 µmol dm day at the seep stations. Four lineages of anaerobic methanotrophic archaea (ANME) (1, 2a-2b, 2c, and 3) were found in the deeper sediments at the seep stations along with sulfate-reducing . The ANME-2a-2b clade was predominant among ANME. Aerobic ammonium-oxidizing (family ) predominated in the upper sediments along with heterotrophic and , and mehtanotrophs of the classes () and (families and ). Members of the genera and occurred in the sediments of the seep stations. Mehtanotrophs of the classes () and (families and ) occurred in the sediments of all stations. The microbial community composition was similar to that of methane seep sediments from geographically remote areas of the global ocean.