A Review of Mechanisms of Resistance to Heavy Metals in Microorganisms and Their Applications in Bioremediation

One of the most important issues in the world is the environmental pollution caused by toxic metals. Human activities such as the extraction of metals from mines, industrial wastes production led to the heavy metals accumulation in the environment that cause toxic effects on living organisms. On the other hand, the only way of environmental cleanup is metal removing, recycling and reusing, due to lack of metals biodegradability. For this purpose, the use of biological processes and microorganisms is one of the adopted solutions. Biological processes are based on interactions between microorganisms and metals. The identification of microorganisms resistant to metals plays an important role in the removal of environmental pollution. In order to survive, microorganisms can be resistant to heavy metals by different mechanisms as they contacted with metals. In this paper, the effects of toxic metals on microorganisms, resistance mechanisms, and applications of resistance mechanisms to metals such as bioaccumulation, biosorption, biotransformation, biomineralization and bioleaching of metals have been studied. The results illustrate that the use of microorganisms is a natural, sustainable and economical solution to recycle wastes and clean up the environment from heavy metals and could have a high percentage of valuable and toxic metals recovery and/or detoxification.