Advances in characterizing microbial community change and resistance upon exposure to lead contamination: Implications for ecological risk assessment

Recent advancement in molecular techniques has spurred numerous studies on responses of microorganisms to lead exposure, leveraging detailed phylogenetic analyses and functional gene identification to discern the effects of lead toxicity on microbial communities. A comprehensive review of recent research is provided on (1) lead resistance mechanisms of microorganisms; (2) microbial community changes in contaminated aquatic sediments and terrestrial soils; and (3) lead resistance genes applied to lead biosensor development. Ample evidence in the literature, including both in vitro and in situ studies, indicates that exposure to lead inhibits microbial activities (such as respiration and metabolism), reduces biomass and alters microbial community structure. Even at sites where microbial communities do not vary compositionally with contaminant levels, functional differences between microbial communities are evident. The main mechanisms of lead resistance involve extracellular and intracellular biosorption, precipitation, complexation, and/or efflux pumps. The suites of genes associated with lead resistance mechanisms can serve, when considered with phylogenetic information, as indicators of lead contamination. This holds potential for development of next generation lead biosensors. To promote applications of advanced knowledge, molecular techniques, and lead biosensor technology, perspectives on using microbial indicators for site ecological assessment are presented.