Molecular mechanisms of resistance to heavy metals in bacteria and their applications in bioremediation

Abstract

Heavy-metal dissemination in superficial sediments and subground water is considered as a worldwide
problem and its solution constitutes a challenge for the environmental cleaning-up. Several heavy-metals are essential
nutrients required in trace concentrations for bacteria (range of nanomolar); however they are toxic in concentrations
higher than micromolar. Heavy metals are considered as a biological threat for microorganisms because these elements
are not biodegradable, contrary to organic pollutants. Only microorganisms encoding heavy metal resistance genetic
determinants are able to survive in environments with high concentrations of these elements. Currently, heavy metals
containing wastes are treated basically by chemical and physical methods but these are complicated, expensive and their
efficiency is low. Release of great volumes of liquid and solid wastes which still contain high amounts of heavy metals is
another of the disadvantages of the aforementioned methods. Bioremediation of effluents and waste waters using heavy
metal resistant microorganisms based technologies may provide an alternative for environmental protection. Microorganisms
might be effective metal accumulators and evidences support that the biomass-based clean-up processes are
economically viable. However, many aspects of metal-microbe interactions remain unknown and unexploited in biotechnology.
The application of bioremediation processes required a deeper knowledge of the biotransformation pathways and
genetic determinants encoded by organisms from indigenous microbial communities of these ecosystems. The aim of
this paper is to review the molecular mechanisms of heavy metal resistance described in bacteria and their applications
in bioremediation.
Introducción
La contaminación ambiental