Research progress on the effect of heavy metal exposure on the evolution of antibiotic resistance genes in the environment

Antibiotic resistance genes (ARGs) have been listed as an emerging contaminant in the environment. Their pollution dissemination and environmental evolution have become the attentive focuses and research hotspots in the field of ecological environment. Due to their non-degradability, heavy metals can stably exist in the environment and have long-term bioavailability, posing a continuous selection pressure on ARGs. The different resistant mechanisms of bacteria to antibiotics and heavy metals, as well as their synergistic effects were summarized. The influence of heavy metals on the environmental behaviors including gene abundance and horizontal transfer of ARGs was emphatically discussed. The results showed that a variety of heavy metals and their compounds would affect the abundance and horizontal transfer of ARGs. Different types and concentrations of heavy metals may have different effects. Heavy metals affected the horizontal transfer of ARGs mainly by affecting the secretion of EPS, changing the cells permeability, and affecting genes’ expression, etc. Different types of heavy metals could affect the horizontal transfer of ARGs in different ways. Although there had been many research reports on the impact of heavy metals on the environmental behavior process of ARGs, the internal mechanism of the influence of heavy metals on ARGs and the synergistic selection effect of heavy metals on the abundance and horizontal transfer of ARGs in different environmental media need to be further studied.