Microbial stress response to heavy metals in the environment
Heavy metal contamination is a global environmental issue as it poses a significant threat to public health, and exposure to metals above a certain threshold level can cause deleterious effects in all living organisms including microbes. To survive in such harsh environments, some microbes evolved a few defence mechanisms to metabolize and transform heavy metal into a less hazardous form, resulting in the formation of heavy-metal-resistant microbes. Heavy-metal-resistant microbes can be used in bioremediation to remediate the contaminated areas. Bioremediation uses natural biological activities, is relatively low-cost, and has high public acceptance. Herein, we summarize the interactions and mechanisms that occur between the microbes and heavy metal, including stress responses and defence mechanisms, which involve aggregation and biofilm formation, production of extracellular polymeric substances (EPS), and development of resistance genes and signalling pathways against heavy metals.