Depth-Stratified Microbial Communities Drive Methane Cycling and Mercury Methylation in East Dongting Lake Sediments

Lake sediments are significant sources of methane and hotspots for microbial-mediated biogeochemical processes, including anaerobic oxidation of methane (AOM) and mercury methylation. This study investigated the microbial community composition and diversity in surface sediments of East Dongting Lake (EDL) at three depths (deep, middle, and shallow layers). Results revealed distinct microbial communities across depths, with Crenarchaeota dominating the deep layer and Chloroflexi prevalent in middle and shallow layers. Methanogens, primarily acetotrophic and hydrogenotrophic, exhibited higher abundance in the middle layer, correlating with elevated total organic carbon (TOC). AOM microorganisms, including ANME-1 and Desulfosarcinaceae, varied with depth, with ANME-1 dominating the deep layer. Mercury-methylating microorganisms, notably Bacillus, were abundant in the deep layer, linked to higher methylmercury (MMHg) concentrations despite low total mercury (THg). Environmental factors such as pH, TN, and THg significantly influenced microbial composition. The presence of Desulfobulbus, involved in both sulfate-dependent AOM and mercury methylation, highlights its ecological role. These findings enhance understanding of methane and mercury cycling in freshwater sediments, emphasizing the interplay between microbial communities and environmental conditions.