Bacterial Homeostasis and Tolerance to Potentially Toxic Metals and Metalloids through Diverse Transporters: Metal-Specific Insights

The dependence on metals and metalloids significantly impacts global heavy metal pollution and the fate of living organisms on this planet. Microorganisms like bacteria are no exception, and due to continuous exposure to metalliferous environments, many bacteria have evolved heavy metal resistance. Bacteria can also detoxify and subsequently remove the toxic metals using a variety of mechanisms. Efflux systems and associated transporter proteins are integral to heavy metal homoeostasis, tolerance, and detoxification in bacteria. Transport proteins are crucial for facilitating the transfer of hydrophilic substrates across hydrophobic membranes, constituting a varied array of proteins with distinctions in topology, substrate specificity, energy coupling mechanisms, and sequence similarity. This category of transporter proteins encompasses P-type ATPases, RND (resistance, nodulation, cell division), CDF (cation diffusion facilitator), ATP binding cassette (ABC) transporters, HoxN, CHR, MIT family proteins, and more. This article provides metal-specific insights into transporters, delineating their functions in bacterial resistance and homeostasis concerning potentially toxic metals and metalloids. The roles of assorted genes and operons in fulfilling this purpose and the physiological impact of different heavy metals on bacterial cells are also elaborated upon in this review.