Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient

Marine hydrothermal vents are extreme environments that naturally select for organisms with strong resistance and the ability to cope with special conditions of acidification. Sea anemones are an interesting example that are able to buffer intracellular pH conditions. In this study, the influence of a natural pH gradient on microbial communities associated with Anemonia viridis (Cnidaria, Anthozoa) tentacles was investigated. We hypothesized that exposure to a natural pH gradient would be associated with changes in the structure and activity of A. viridis-associated microbial communities, potentially contributing to the host's resilience in hydrothermal environments. Microbial enzymatic activities within anemones' tentacles were investigated by incubation with fluorogenic compounds. The leucine amino peptidase activity was highest in the tentacles of specimens living in more acidified sites. A microbial biodiversity loss was observed in bacterial symbionts from less acidified to more acidified sites, with a reduction of relative abundance in certain groups (i.e., Planctomycetota, Firmicutes, and Desulfobacterota). Results obtained by a metabarcoding approach provided interesting insights into the taxonomic shifts of the A. viridis holobiont system in naturally acidified environments.