Taxonomic and Functional Metagenomic Investigations of Microbial Communities in Authigenic Carbonate Crust (ACC) Sediment

Abstract

The formation of authigenic carbonate crust (ACC) and its burial in marine sediments accounts for around 80% of the total carbon removed from the Earth’s surface. To access the microbial diversity associated with ACC in the Ulleung Basin, East Sea of Korea, we compared microbial community between ACC and carbonate-free sediments using quantitative PCR (Q-PCR) and 16S rRNA gene tag pyrosequencing. The abundance of archaeal and bacterial 16S rRNA gene copies in ACC sediment were 4.0 and 11.3 times higher than carbonate-free sediment, respectively. Furthermore, ANME-1 (1.75×107±6.80×105 copies/gwet) and ANME-2c (1.08×107±1.94×105 copies/gwet) was only detected in ACC sediment. Based on the partial sequences of 16S rRNA gene revealed that ANME groups were only identified in ACC sediment, accounting for half of the archaeal proportion with following order: ANME-1 (25.0%), ANME-2a/b (18.8%) and ANME-2c (6.0%). We obtained 3.6 G bp (13 million reads with average sequence length of 278 bp) of metagenomic sequences from ACC sediment. Taxonomic profiling showed that sequencing reads related with Methanosarcinales and Vibrionales were overrepresented accounting for 16.9% and 14.1% of total reads, respectively. The de novo assembly of single reads from ACC datasets resulted in 43,648 contigs (>1 kb in length). The mappping analysis of contigs to reference genomes showed that most of the contigs were aligned to ANME-1 and ANME-2a draft genome, not methanogens. This study serves as a relationship between authigenic carbonate crust formation and anaerobic oxidation of methane by ANME groups in marine sediments.