Microbial Diversity In Cold Seep Marine Sediments Of The Dongsha Area In South China Sea

The microbial diversity and abundance in a cold seep sediment core (555 cm long) of the Dongsha Area in northern South China Sea was assessed and correlated with methane concentration throughout the core with the use of an integrated approach including geochemistry (sediment pore water chemistry) and culture-independent microbiology [acridine orange direct count (AODC) and phylogenetic analysis].The AODC result showed that microbial cell abundance was 105-107cells per gramme sediment throughout the core. The variation of the microbial abundance was positively correlated with methane concentration: the higher methane concentration, the higher microbial abundance and vice versa, indicating that methane concentration was a major factor controlling the microbial cell distribution.The phylogenetic analysis showed a wide variety of uncultured bacteria and archaea were present in the studied sediment core. The major group affiliation analysis indicated that the microbial diversity in the studied cold seep sediment core retrieved from South China Sea was much higher than that in other cold seeps worldwide (i.e. the Peru Margin, the Gulf of Mexico). Archaeal clone sequences could be grouped into the Euryarchaeota and the Crenarchaeota domains: the retrieved euryarchaeotal sequences belonged to Marine Benthic Group (MBG)-D, Halobacteriales, Anaerobic Methane Oxidation Group (ANME)-I, South African Gold Mine Euryarchaeotic Group (SAGMEG), Antarctic Deep Lake (ADL) and two unclassified Euryarchaeotic Clusters; and the retrieved crenarchaeotal sequences belonged to MBG-B (a group of archaea that were putatively thought to be confined to gas hydrate-, methane-, organic carbon-rich marine sediments), MBG-C, Miscellaneous Crenarchaeotic Group (MCG), Marine Crenarchaeotic Group I (MGI) and C3, among which the clone sequences affiliated with MBG-B were the most abundant (23.9% of the total archaeal clones).The retrieved bacterial clones were grouped into Proteobacteria (including?-,?-,?-,?-,?-subclass), Planctomycete, Firmicutes, Chloroflexi, Actinobacteria, Acidobacteria, Spirochaetes, Verrucomicrobia, Chlorobi, candidate divisions TM6, OP3, OP8, OP11 and WS3, and unclassified bacteria, among which clones affiliated with Proteobacteria were the most abundant (53.6% of the total bacterial clones)In summary, the positive correlation between microbial abundance and methane concentration and the presence of clones affiliated with ANME-I and MBG-B indicated that the studied cold seep sediments may be undergoing a coupled process of methane oxidation and sulfate reduction. However, presence or absence of gas hydrates in the sampling area could not be determined with certainty without further evidence.