Microbial communities in semi-consolidated carbonate sediments of the Southwest Indian Ridge.

White semi-consolidated carbonate sediments attached to black ferromanganese oxide films were collected approximately 50 km west of a newly discovered hydrothermal field near the Southwest Indian Ridge (SWIR). The biodiversity of the prokaryotic communities within the field was examined using clone library-based culture-independent analysis of the exterior black oxides and the interior white carbonates. Subsequent 16S rRNA gene analysis suggested that Gamma-proteobacteria, Acidobacteria, and Thaumarchaeota members dominated the bacterial and archaeal clone libraries. To further characterize the metabolic processes within the microbial community, analyses of the amoA (coding the alpha subunit of the ammonia monooxygenase for Archaea) and aprA (coding the alpha subunit of the dissimilatory adenosine-5'-phosphosulfate reductase for the sulfate-reducing and sulfur-oxidizing prokaryotes) functional genes were conducted. The functional gene analysis results suggested that Thaumarchaeota and Alphaproteobacteria members were the potential players that participated in N and S cycles in this marine carbonate sedimentary environment. This paper is the first to describe the microbial communities and their potential metabolic pathways within the semi-consolidated carbonate sediments of the SWIR.