Adaptation of soil microorganisms to trace element contamination: a review of mechanisms, methodologies and consequences for risk assessment and remediation.

This review provides an updated and integrated view of the adaptation of soil microorganisms to elevated concentrations of trace elements. Starting with a summary of the occurrence of trace elements in soils and their effects on soil microorganisms, the scientific evidence underlying adaptation of microorganisms to trace elements from species to community level is discussed. Insights are given regarding the main physiological processes involved in the resistance of bacteria to toxic elements including the potential importance of horizontal gene transfer in the adaptation process. The review continues with a discussion of how new molecular and biotechnological techniques can enrich this field of study. Scientific evidence is utilized in constructing an illustration of microbial community responses with reference to ecological indicators during various adaptation stages, while the related effects on community biological functionality and resilience are discussed. We conclude with an evaluation of the importance of considering adaptation in risk assessment and possible remediation of trace element contaminated sites.