Microbial Diversity in the Deep Marine Sediments from the Qiongdongnan Basin in South China Sea

Abstract

The continental shelf and slope in the northern South China Sea is well known for its prospect of oil/gas/gas-hydrate resources. To study microbial communities and their roles in carbon cycling, a 4.9-m sediment core was collected from the Qiongdongnan Basin on the continental slope of the South China Sea during our cruise HY4-2005-5 in 2005. Geochemical, mineralogical, and molecular phylogenetic analyses were carried out. Sulfate concentration in pore water decreased with depth. Abundant authigenic carbonates and pyrite were observed in the sediments. The bacterial community was dominated by aerobic and facultative organisms. Bacterial clone sequences belonged to the Gamma-, Alpha-, Deltaproteobacteria and Firmicutes group, and they were related to Fe(III) and/or Mn(IV) reducers, sulfate reducers, aromatic hydrocarbon degraders, thiosulfate/sulfite oxidizers, and denitrifiers. Archaeal clone sequences exhibited greater overall diversity than the bacterial clones with most sequences related to Deep-Sea Archaeal Group (DSAG), Miscellaneous Crenarchaeotic Group (MCG), and Uncultured Euryarchaeotic Clusters (UECs). Archaeal sequences related to Methanosarcinales, South African Gold Mine Euryarchaeotic Group (SAGMEG), Marine Benthic Group-D (MBG-D) were also present. Most of these groups are commonly present in deep-sea sediments, particularly in methane/organic-rich or putative methane hydrate-bearing sediments.

Keywords:

• 16S rRNA gene analysis
• Archaea
• Bacteria
• diversity
• South China Sea

Acknowledgments

This research was partly supported by National Science Foundation grant EAR-0345307 to HD and National Science Foundation of China (40228004, 40472064). The authors wish to thank Dr. Richard Edelmann for his valuable assistance in SEM observations and John P. Morton for his help in cation and anion analysis. We are grateful to Tim Williams and one anonymous reviewer for improving the quality of this manuscript.

Hailiang Dong is also affiliated with Geomicrobiology Laboratory, China University of Geosciences, Beijing, 100083, China.