Supplemental Information for Materials and Methods from Cellular mechanisms underlying extraordinary sulphide tolerance in a crustacean holobiont from hydrothermal vents

The shallow-water hydrothermal vent system of Kueishan Island has been described as one of the world's most acidic and sulphide-rich marine habitats. The only recorded metazoan species living in the direct vicinity of the vents is Xenograpsus testudinatus, a brachyuran crab endemic to marine sulphur-rich vent systems. Despite the toxicity of hydrogen sulphide, X. testudinatus occupies an ecological niche in a sulphide-rich habitat, with the underlying detoxification mechanism remaining unknown. Using laboratory and field-based experiments, we characterized the gills of X. testudinatus that are the major site of sulphide detoxification. Here sulphide is oxidized to thiosulphate or bound to hypotaurine to generate the less toxic thiotaurine. Biochemical and molecular analyses demonstrated that the accumulation of thiosulphate and hypotaurine is mediated by the sodium-independent sulphate anion transporter (SLC26A11) and taurine transporter (Taut), which are expressed in gill epithelia. Histological and metagenomic analyses of gill tissues demonstrated a distinct bacterial signature dominated by Epsilonproteobacteria. Our results suggest that thiotaurine synthesized in gills is used by sulphide-oxidizing endo-symbiotic bacteria, creating an effective sulphide-buffering system. This work identified physiological mechanisms involving host-microbe interactions that support life of a metazoan in one of the most extreme environments on our planet