Characterization of mercury resistance mechanisms in marine sediment microbial communities.

While estuarine sediments are often severely polluted with mercury, few studies have focused on the mechanisms of adaptation to mercury contamination in marine sediment microbial communities. In this study, we report a high frequency of Gram-negative bacterial isolates that are resistant to the heavy metal mercury obtained from the aerobic culturable marine microbial community. We detected a low frequency of genes homologous to mer(Tn21) in isolates from three out of four different estuarine environments. Other mercury resistant culturable bacterial isolates lacking homology to the known mer genes were able to reduce Hg(II) to its volatile Hg(0) form, indicating the presence of divergent mer genes. In addition, a number of mercury resistant isolates, obtained from three of the four marine sites investigated, exhibited decreased resistance to mercury in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone. Representative mercury resistant bacterial isolates were identified by phylogenetic analysis as belonging to the alpha and gamma subclasses of the class Proteobacteria.