Woesearchaeal metagenome-assembled genome informs its role in blue hole water column and sediments

Blue holes are nearshore subsurface caverns formed in calcareous bedrock that feature biogeochemical characteristics distinct from the surrounding seafloor. Their rims are biological hot spots, with rich communities of invertebrates and high biomass of fish and other macrofauna. Blue holes have relatively shallow (~10-50 m) openings and hypothesized depths up to 150 m. Due to their narrow openings, they remain underexplored and harbor poorly understood microbial habitats. Our team used a combination of a robotic lander and technical SCUBA diving to sample the water column and sediment microbial communities of a West Florida Shelf blue hole. We will present the metagenome-assembled genomes from these environments, with particular focus on a Woesearchaeotal lineage. The Woesearchaeota are a poorly understood archaeal phylum whose members have been observed in anoxic freshwater and marine systems but whose biochemical roles are unknown. This taxon comprised up to 40% of the water column community below the oxycline around 100 m, which also featured elevated sulfide levels. Bioinformatic analyses are ongoing but we anticipate this will be the most complete genome thus far reported from this phylum, which has no cultured representatives. Combined with the chemical features of the water column and sediments, we will describe metabolic pathways and potential biogeochemical roles of this organism. These likely include a strict anaerobic lifestyle and possible syntrophy with a sulfate-reducing gammaproteobacterial clade. Characterization of this microbial taxon has important implications for understanding the unique biogeochemistry of blue hole systems, as well as other shallow oxygen minimum zones worldwide.