Methanotrophs and Co-occurring Microbial Taxa: Genomic Potential for Carbon, Nitrogen, and Sulfur Cycles in Newly Formed High-altitude Proglacial Lakes.
The extreme and fragile environments of high-altitude proglacial lakes shape unique microbial communities and metabolic networks, serving as active interfaces in the biogeochemical cycles of carbon (C), nitrogen (N), and sulfur (S). However, the metabolic processes underlying microbially driven biogeochemical cycling in these lakes remain poorly understood. In this study, by integrating field investigations and isotopic analyses across multiple seasons, we observed geochemical and genomic evidence consistent with significant microbial methane (CH4) oxidation in the surface sediments of cryo-oligotrophic proglacial lakes in the Nyainqentanglha Range on the Tibetan Plateau. Metagenome-assembled genomes (MAGs) analysis revealed that Methylobacter was the dominant methanotroph in surface sediments, possessing complete pathways for aerobic CH4 oxidation, partial denitrification (nitrate → nitrous oxide), and sulfide oxidation (sulfide → elemental S), suggesting its genetic capacity to potentially participate in C, N, and S transformations. The co-occurring Nitrospira (Palsa-1315) was identified as a key player in the N cycle through complete ammonia oxidation (comammox, ammonia → nitrate), while Rhodoferax and Thiobacillus were considered important contributors via heterotrophic and autotrophic denitrification (nitrate → dinitrogen), respectively. Additionally, Thiobacillus may be the key genus involved in the S cycle through S/sulfide oxidation (S0/sulfide → sulfate). Overall, this study reveals the key microbial taxa involved in CH4, N, and S cycling and highlights the potential importance of methanotrophy in rapidly expanding proglacial ecosystems amid ongoing climate warming.