Research Product

The role of mer(Tn21) in adaptation of aquatic microbial communities to Hg2+ was investigated. Elemental mercury was the sole product of Hg2+ volatilization by freshwater and saline microbial communities. Bacterial activity was responsible for biotransformation because most microeukaryotes did not survive the exposure conditions, and removal of larger microbes (>1 µm) from adapted communities did not significantly (P >0.01) reduce Hg2+ volatilization rates. DNA sequences homologous to mer(Tn21) were found in 50% of Hg2+ resistant bacterial strains representing two fresh water communities, but in only 12% of strains representing two saline communities (the difference was highly significant; P < 0.001). Thus, mer(Tn21) played a significant role in Hg2+ resistance among strains isolated from freshwaters where microbial activity had a limited role in Hg2+ volatilization. In saline environments where microbially mediated volatilization was the major mechanism of Hg2+ loss, other bacterial genes coded for this biotransformation.