Stratification of Microbial Community in Marine Sediments of the Ross Sea, Antarctica

Abstract

The deep subseafloor biosphere is the least-understood habitat on Earth, even though the amount of microbial biomass therein plays important roles in the biogeochemical cycles and remineralization of organic materials. In this study, microbial community of 21 sediment horizons from one gravity core (approximately 4 m) collected in the Ross Sea was profiled by pyrosequencing. Distinct stratification in the microbial community within the gravity core was observed. Bacterial community showed distinctive stratification from Proteobacteria, Planctomycetes, Bacteroidetes, Acidobacteria, and Chlorobi in the aerobic upper sediment column towards OP9, Chloroflexi, and Actinobacteria in anaerobic sediment horizons. Interestingly, uncultured candidate phylum OP9 was predominant from 40 cm below seafloor composing upto 54.2%, indicating initial constraints for their microbial habitat preferences. Archaea also showed a dramatic shift in community composition at the oxic-anoxic transition zone as was the case for bacteria. Crenarchaeota was the most dominant archaeal phylum throughout the sediment. However, relative abundance of Crenarchaeota classes varied considerably along the depth. Eukaryotic community showed Stramenopiles and unassigned group to any phyla were dominant throughout the sediment. However, relative abundance of Alveolata and Metazoa showed significant decrease along sediment depth, especially across the oxic？anoxic transition.