Comparative Study On The Archaeal Diversity Of Two Deep-sea Sediment Columns Collected From Northern South China Sea

Marine biosphere is among the least-understood habits on earth, even through the huge microbial biomass therein plays an important role for potential long-term control on global biogeochemical cycles. South China Sea is the largest sea around China, It significantly influences the climate and environment of China. The study on the sedimental microbial community of South China Sea is helpful for us to understand the diversity of microbes living there and their influence of the whole ecological system.In this paper, the vertical and geographical distribution of archaea and their diversity in the Methane-rich region of the Northern South China Sea were investigated with PCR-based gene library construction method. Sediment column SCS1 was divided into 7 zones, the sediment column SCS2 was divided into 6 zones, expect for zone 7, the others were the same in depth. After 581 gene sequences of 13 Libraries were analyzed using DOTUR software, 102 Operation Taxonomic Units (OTU) were obtained. The similarity between the 16S rRNA gene sequences obtained and those deposited in NCBI database varied from 80% to 99%. Molecular phylogenetic analysis showed that all clones belonged to Crenarchaeota and Euryarchaeota. Crenarchaeota included Miscellaneous Crenarchaeotic Group (MCG), Marine Group I (MGI) and Deep-Sea Archaeal Group(DSAG). Euryarchaeota included South African Gold Mine Euryarchaeotic Group (SAMEG), Marine Benthic Group D(MBGD) and Novel Euryarchaeotic Group(NEG). The similarest sequences of MGI fund in database were found to represent the microbes involved in the oxidation of ammonia, of them, Nitrosopumilus maritimus SCM is a culturable archaeal ammoxidator. These finding indicated that MGI was an Ammoxidation group, involving in the biogeochemical cycles of nitrogen. Miscellaneous Crenarchaeotic Group and Marine Benthic Group D were the two most dominant aechaeal 16S rRNA gene clone groups in two columns. MCG was the predominent phylotype in the top zone of SCS1 and SCS2.The archaeal phylotype of SCS1 is basically as same as that of SCS2.Using DOTUR software, Shannon-Weaver index, Simpson Index, Chao1 Index and ACE Index each library were calculated. For the two columns, diversity was generally low, but increased with depth. The results indicated that diversity of each zone of SCS1 was higher than that of corresponding zone of SCS1. Our data suggested that the community structure and diversity of archaea varied greatly with depth, possibly being relating with the change of physical and chemical conditions. The recognition of archaeal group prevailingness under distinctive subseafloor environment is a key step toward determining the role these communities play in Earth′s essential biogeochemical processes.