Metabolic potential of the microbial community along a depth gradient in Lake Kinneret sediments

Despite the crucial role of lake sediments in global biogeochemical cycling as a source of the greenhouse gas methane, our understanding the intrinsic microbial communities and their role in geochemical cycles in this environment is limited. Here, we used metagenomics and geochemical analyses to assess the microbial methane, iron, sulfur, and nitrogen cycling in depth profiles of sedimental samples from lake Kinneret, a warm monomictic subtropical lake. In these sediments microbes catalyze anaerobic methane oxidation and iron reduction beneath the sulfate reduction and the main methanogenic zones. High quality metagenome-assembled genomes revealed a broad potential for respiratory sulfur and nitrogen metabolism. Wood-Ljungdahl pathway used by acetogens and methanogens was found to be highly common given the widespread occurrence of the genes encoding the key enzyme carbon-monoxide dehydrogenase. Acetate, alcohol, and hydrogen are the prominent substrates for the fermentative metabolism. Methane metabolism was found in Methanotrichales Methanomicrobiales, Methanomethyliales, ANME-1 and Methanomassiliicoccales, and the bacterial Methylomirabilales. Iron reduction genes such as porins, MtrABC and outer membrane cytochromes were observed in Thermodesulfovibrionales, Geobacterales, Burkholderiales and Myxococcales. Our results indicated flexible metabolic capabilities of core microbial community, which could adapt to changing redox conditions.