Genome-Resolved Approach of Guerrero Negro Hypersaline Microbial Mats Reveals the Metabolic Potential of Key Players in a Stratified Community.

Hypersaline microbial mats at Guerrero Negro harbor a stratified, highly diverse community with diel metabolic changes. While oxygenic photosynthesis and sulfate reduction are the dominant bacterial metabolic processes, methylotrophic methanogenesis is the main archaeal pathway. Although these metabolic processes have been biochemically characterized, the identity and encoded metabolism of the microorganisms have been inferred only from gene-marker data. Here, a genome-resolved approach in both environmental, as well as experimental dark condition samples (control, H2/CO2, TMA, and H2/CO2-TMA) was used to stimulate less-known anaerobic strategies, determine the metabolic potential of the main microbial players, and analyze the community. Representative metagenome-assembled genomes (170 MAGs) were obtained, encompassing 25 bacterial and 4 archaeal phyla. The metabolic analyses of three basic elements (carbon, sulfur, nitrogen) encoded in the MAGs suggested that in environmental samples, phototrophic taxa were the main source of the organic matter that fueled most of the community. Different sulfur species acting as electron acceptors led to the metabolism of partially degraded organic matter in the lower layers of the mat. These results link and clarify the biochemical processes and microbial players, adding a novel genomic component for the ecological understanding of the microbial mats of Guerrero Negro.