Adaptation of Aquatic Microbial Communities to Hg 2+ Stress

Abstract

The mechanism of adaptation to Hg 2+ in four aquatic habitats was studied by correlating microbially mediated Hg 2+ volatilization with the adaptive state of the exposed communities. Community diversity, heterotrophic activity, and Hg 2+ resistance measurements indicated that adaptation of all four communities was stimulated by preexposure to Hg 2+ . In saline water communities, adaptation was associated with rapid volatilization after an initial lag period. This mechanism, however, did not promote adaptation in a freshwater sample, in which Hg 2+ was volatilized slowly, regardless of the resistance level of the microbial community. Distribution of the mer operon among representative colonies of the communities was not related to adaptation to Hg 2+ . Thus, although volatilization enabled some microbial communities to sustain their functions in Hg 2+ -stressed environments, it was not mediated by the genes that serve as a model system in molecular studies of bacterial resistance to mercurials.