Biological Nitrogen Fixation Driven by Methane Anaerobic Oxidation Supports the Complex Biological Communities in Cold-Seep Habitat

Abstract

Cold seeps represent a class of chemosynthetic ecosystems that are prevalent in deep-sea environments. Despite being biological hotspots with numerous new species discoveries, the microbial functional dynamics at the Haima cold seep, which is located along the northwest continental slope of the South China Sea, remain largely unexplored. Here, we employed metagenomic sequencing to investigate the microbial communities of the Haima cold seep sediments, paying particular attention to microorganisms participating in biogeochemical cycles at varying spatial scales. In the surface layer of regular sediment areas, the various sulfur-oxidizing bacteria Chromatiates, PS1, SZUA-229 and GCF-002020875 were the most numerically abundant groups, which recycle sulfide and generate sulfate with nitrate removal to support the methane anaerobic oxidation in subsurface layer. However, in the biogenous sediments of cold seep ecosystems, methane anaerobic oxidation and nitrogen fixation emerge as the predominant pathways. The microbial coupling groups sulfate reducing bacteria C00003060 and ANME-1 use the electrons and energy from methane anaerobic oxidation to complete nitrogen fixation metabolic pathway. These data suggest that the cold-seep diazotrophs can support complex biological communities by providing them with the fixed nitrogen. This study expands our understanding of the functional microbial structure and metabolic capabilities of the cold seep ecosystem.

Keywords: Cold seep, Element cycling, Methane anaerobic oxidation, Nitrogen fixation