Microbial technologies for heavy metal remediation: effect of process conditions and current practices

Heavy metal (HM) contamination is a persisting environmental problem in many countries. The major sources of soil contamination due to heavy metals (HMs) include pesticides, organic compounds, paints, waste generation by industrial (including small and medium enterprises) and mining activities. The remediation of soils contaminated with HMs is essential, given the fact that the latter causes direct and indirect damage to living organisms and the environment. There have been efforts to tackle the indefinite persistence of HMs in the soil for a long time; however, the problem persists due to a surge in HM utilization and lack of proper technologies for their eradication. To prevent HM contamination in the environment, novel, resilient ecotechnologies are necessary to remove and recover HMs from contaminated water and soil environments. Microbial bioremediation offers a cost-effective solution for the treatment of environmental sites contaminated with HMs. Microbes have the capacity to degrade environmental pollutants through their metabolic activity. Microbial degradation of HMs proceeds through diverse processes, such as biosorption, bioleaching, biomineralization, biotransformation and intracellular accumulation. The use of genetically modified microorganism with increased bioremediation potential, biomining using hybrid technologies and omics-based approaches is helpful to explore the realms of HM bioremediation. The implementation of these (bio) technologies has assisted in restoring soil contaminated by HMs and in protecting the environment. This review compiles information on the recent advances and applications of microbe-mediated bioremediation of soils contaminated with HMs.Graphical abstract