Resumo

Marine sponges are ecologically diverse hotspots of unexplored microbial communities and essential components of marine benthic communities. Bacterial symbionts constitute 30–60% of the sponge mesohyl, mostly occurring as intracellular symbionts (endosymbionts). In addition to the production of bioactive compounds, the bacteria associated with the sponges can be used as indicators of contamination in the marine ecosystem. Mercury is one of the most toxic heavy metals and its level of contamination in the environment has increased over a thousand-fold as a consequence of anthropogenic activities, such as the discharge of wastewaters from chlor-alkali plants, the incineration of coal and metal mining. So, ionic and organic forms of mercury (Hg) are powerful cytotoxic and neurotoxic agents in both humans and wild life. In this study, it was analyzed the resistance patterns of cultivable bacteria isolated from eleven sponge species on the coast of Rio de Janeiro (Praia Vermelha beach and Cagarras Archipelago), Brazil to inorganic mercury and methylmercury and the possible role of these bacterial strains in detoxification. In addition, it was evaluated the mercury resistant bacteria (MRB) for their capacity to volatilize Hg2+ and their capacity of biosurfactant production. Out of the 1,236 colony forming units (CFU) associated with eleven species of marine sponges, 100 morphologically different bacterial strains were analyzed in this study. Of these, 21 strains were resistant to Hg, 14 of which were classified as highly resistant because they grew despite exposure to 100 µM HgCl2. Fifteen resistant strains reduced Hg and presented merA in their genomes. The remaining six strains produced biosurfactants, suggesting that they may tolerate Hg by sequestration. Eleven strains grew in the presence of methylmercury (MeHg), two in media supplemented with 2.5 µM of MeHg, four with 10 µM and five with 20 µM. Our results suggest a potential for mercury detoxification by marine sponge-associated resistant bacteria, either through reduction or sequestration, as well as the possibility of bioremediation of toxic waste containing mercury.