Cold seeps are deep-sea extreme environments where deeply sourced methane-rich geofluids discharge from the deep subsurface to the sediment-water interface (SWI). The SWI of cold seeps hosts numerous chemolithotrophic microbial communities, which drive element cycles and enhance methane consumption. However, little is known about the metabolic processes of dominant microbes in the SWI of various habitats in cold seeps. In this study, we used metagenomic and metatranscriptomic approaches to investigate the composition and metabolic activity of microbial communities across distinct habitats (high-methane-plume, low-methane-plume, and seep-biota sites) at two active cold seeps in the South China Sea. Methylomonadaceae capable of methane oxidation were predominant in methane-rich sites, Beggiatoaceae was the major bacterial group and only presented in the sulfide-rich site. Genes encoding aerobic methane oxidation (AeOM) were highly expressed in almost all sampling sites, while genes encoding denitrification were highly expressed in low-methane-plume and sulfur oxidation processes in low-methane-plume and seep-biota sites. Some novel Methylomonadaceae genomes were identified, and genes encoding denitrifying and sulfur/thiosulfate-oxidizing enzymes were found to be highly expressed in low-methane-plume and seep-biota sites. Furthermore, we also verified via Stable Isotope Probing (SIP) experiments that nitrate and thiosulfate could stimulate Methylomonadaceae to oxidize methane under hypoxic conditions. The global distribution pattern of these methanotrophs showed that they were widespread in marine methane-rich environments. Our findings demonstrate that aerobic methane oxidation was the dominant metabolic process in the SWI of cold seeps, in which aerobic methanotrophs could couple denitrification and Sox pathways to methane oxidation in oxygen-limited niches across various habitats. Nitrate and thiosulfate could stimulate AeOM in surface sediment of cold seeps. By global metagenomic analysis, these methanotrophs are frequently distributed in marine methane-rich and hypoxic environments, such as cold seeps and hydrothermal vents. This study provides new insights into the composition and metabolic functions of microbial communities inhabiting various habitats of the SWI of cold seeps, offers a deeper understanding of the aerobic methanotrophic metabolic versatility and adaptation mechanisms in hypoxic and sulfide-rich conditions, and enhances underestimated contributions of aerobic methanotrophs to methane oxidation in the SWI of cold seeps.

暂无