Abstract:

Cold seeps are well developed in Dongsha area, South China Sea, but researches on microbes in cold seeps have been inadequate, especially when the high-throughput sequencing technique is used. In this paper, the archaeal diversity of gravity core 973-5 was analyzed based on high-throughput sequencing. The core was 935 cm long and was collected from the deep-sea cold seep area in Dongsha at a depth of approximately 3,000 m. The cell abundance in the sediments collected by core 973-5 varied from 5.3×10⁸ to 34.0×10⁸ cells/g,which increased with depth. The change trend of cell abundance was similar to that of the methane content. Additionally, it was related to the grain size and total organic carbon (TOC) content. The results obtained using high-throughput sequencing revealed that the predominant archaeal groups were MBGB, C3 and ANME-1,which accounted for 39.9%, 15.8% and 12.0% of the total sequences of archaeal communities, respectively, changing with depth. Large amounts of MBGB and ANME-1 along with the rise of pH in the sediments near the sulfate-methane interface (SMI) at approximately 760 cm might indicate the process of methane anaerobic oxidation. At the bottom of the core, considerable amounts of ANME-1 and ANME-2 were detected. This might demonstrate intensive methane-sulfate redox reaction near SMI as well as the decomposition of gas hydrate and upwelling of methane in the lower part of the core, which are possible nutrients for the ANME group. Compared with other sites in Dongsha area, the higher methane flux was observed in core 973-5, but no methanogens were detected. This suggests that the large quantities of methane might have been transported from the shallow and deep fracture system nearby.

Key words: archaeal diversity, 16S rRNA, high-throughput sequencing, core 973-5, cold seep, Dongsha area, South China Sea