A review on the mechanisms and applications of bacteria in responding, adsorbing and transporting heavy metals.

Abstract

Bioremediation of heavy metal-contaminated sites is currently considered one of the most promising strategies for environmental remediation. Bacteria, with their simple structure and ease of modification, serve as ideal biological resources. Although numerous review studies have examined the mechanisms of microbial adsorption of heavy metals, most focus on macro-level processes. However, there is a lack of systematic research on how microorganisms respond to heavy metal stress and how their cellular components and metabolites in the adsorption and transport of heavy metals. In this review, we collected scientific information on bacterial-mediated bioremediation of heavy metals and conducted a comprehensive induction and analysis of it in combination with our own insights. The results showed that due to their structural composition, bacterial cell walls and membranes serve as barriers against heavy metal stress. Bacterial cells achieve heavy metal adsorption, detoxification, and transport through extracellular adsorption, intracellular chelation, and efflux. Specifically, extracellular adsorption involves ion exchange, complexation, redox reactions, nanoparticle formation, and biomineralization. Intracellular chelation is primarily mediated by bacterial metabolites such as metallothioneins and siderophores, while transport is mainly facilitated by components of efflux systems, including P-ATPases, CDF family proteins, and CBA transporters. This review aims to clarify patterns of organism-environment interactions, advance the development and application of heavy metal biosorbents, and further mitigate the risks of heavy metals to humans and the environment.