Community Structure of Methane-Cycling Archaea in Different Geochemical Zones in Aarhus Bay, Denmark

Methanogenesis and anaerobic oxidation of methane are dominant processes regulating methane cycle in the deep biosphere in marine environments, both of which are executed by microbes. The diversity of methane-cycling archaea has been intensively studied by exploring 16S ribosomal RNA gene and alpha subunit of methyl coenzyme M reductase gene (mcrA). In marine sediments, methanogens and methane-oxidizing archaea are mainly found in methane zone (MZ) and in sulfate-methane transition zone (SMTZ), respectively. However, methane-cycling archaea are also present in zones other than their usual residing geochemical zones. Next generation sequencing of mcrA genes from 5 gravity cores shows that both methanogens and methane-oxidizing archaeal group - ANME-1 are ubiquitous in all biogeochemical zones in Aarhus Bay. We will further discuss below questions: which methanogens and methanotrophs are present and active in the presence of sulfate, and which are restricted in SMTZ or MZ? How do activity and pathway of methanogenesis / methanotrophy change with depth and substrate availability?