Discharge of gas-saturated brines fuels chemosynthetic ecosystem in the deep Eastern Mediterranean Sea

Discharge of gas-rich fluids from the seabed yields unique hotspots of biodiversity in the barren deep Mediterranean Sea offshore Israel. Microbes play a crucial role in this habitat, as they control emissions of the greenhouse gas methane and produce vast biomass through chemosynthesis. Using deep-sea-going robotics, we recently discovered and sampled a system of brine pools at the water depth of 1150 m within Palmahim Disturbance. This system not only accommodates rich chemosynthetic communities but also serves as breeding grounds for deep-sea sharks, suggesting that chemosynthetic microbial productivity at the seafloor has broad ecological implications. We investigate the diversity and functions of these microbes, asking how they interact with the environment and another biota. Metagenomics shows that in brines and adjacent sediments, where we measured very high methane and sulfide concentrations (in the millimolar range), microbes cooperate to catalyze sulfur and methane cycling, as well as degradation of organics. Microbial degradation of organic matter fuels sulfur cycling also at the nearby heavily-bioturbated sediments, which do not receive direct methane inputs. Tubewroms and mollusks, whose nutrition fully relies on their diverse thiotrophic and methylotrophic microbial partners thrive en masse at the brine pool margins. The discovery of this unique deep-sea habitat provides an exciting opportunity to explore microbes in an extreme environment and opens a door for multidisciplinary collaborative studies in various related fields.