Resumo

Most marine sponges harbor large number of microorganisms, about 30–60 % of the sponge mesohyl is constituted of sponge-associated bacteria. The aim of this study was to analyze the resistance profile of bacteria isolated from marine sponges at the coast of Rio de Janeiro (Praia Vermelha beach and Cagarras Archipelago), Brazil, to inorganic and organic forms of mercury (Hg). Praia Vermelha beach is highly contaminated by a mixture of domestic and petroleum wastes, with sediment mercury (Hg) levels at the ppm range, while Cagarras Archipelago is less contaminated. Ionic and organic forms of Hg are considered to be among the most powerful cytotoxic and neurotoxic agents for humans and wild life. For this study, a total of 100 morphologically different bacterial strains associated with marine sponges were isolated. Of these, 21 isolates were resistant to Hg, 14 of which were classified as highly resistant because they grew at 100 µM HgCl2. Eighteen resistant strains reduced Hg and 14 also contained putative merA genes in their genomes. The remaining four strains produced exopolysaccharides suggesting that may tolerate Hg by sequestrations. Eleven strains grew in presence of methylmercury (MHg), two in media supplemented with 2.5 µM of MeHg, four with 10 µM, and five with 20 µM. One of the 20 µM MeHg isolates produced elemental Hg when incubated with 16 µM MeHg. Bacteria recovered from sponges collected at Praia Vermelha beach were more resistant to organic and inorganic Hg than those from Cagarras Archipelago. These findings suggest that the observed different profiles could be due to the higher contamination levels in Praia Vermelha as compared to Cagarras Archipelago. Our results suggest a potential for mercury detoxification by marine sponges-associated resistant bacteria, either by its reduction or sequestration, as well as the possibility of bioremediation of toxic waste containing mercury.