A bacterial view of the periodic table: genes and proteins for toxic inorganic ions

Abstract

Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO2-, AsO4(3-), Cd2+ Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, TeO3(2-), Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite.

Two naphthalene degrading bacteria belonging to the genera Paenibacillus and Pseudomonas isolated from a highly polluted lagoon perform different sensitivities to the organic and heavy metal contaminants

“…It is known that the bacterial resistance mechanisms towards these two elements are related (Silver and Phung 2005) and most probably more effective in the Gram-positive than in the Gram-negative bacterium.…”

Structural and functional genomics of plasmid pSinA of Sinorhizobium sp. M14 encoding genes for the arsenite oxidation and arsenic resistance

“…ArsB permease and ArsC reductase are the key enzymes in the arsenic detoxification systems of most Archaea and Bacteria (Silver and Phung, 2005b). Genes encoding other types of reductases were also identified within the pSinA ars locus: arsH, that encodes an NADPH-dependent FMN reductase and trkA, that encodes a major facilitator superfamily protein.…”

“…The gene product of merR from Gram-negative and Gram-positive bacteria functions as an activator protein for the regulation of mercury (Hg 2+ ) resistance. MerT is an inner membrane uptake protein and MerP is a small protein that binds Hg 2+ in the periplasm, whereas MerA is a reductase enzyme involved in reduction of Hg 2+ to Hg 0 (Silver and Phung, 2005b).…”

Insight into heavy metal resistome of soil psychrotolerant bacteria originating from King George Island (Antarctica)

“…To lessen the toxic effect of heavy metals, many microorganisms have developed efficient resistance mechanisms. To date, three main types of such mechanisms have been described: (i) efflux of toxic ions from bacterial cells, (ii) enzymatic transformations of metals, and (iii) incorporation of heavy metals into complexes by metal-binding proteins, which makes them less toxic to the cell (Silver and Phung le 2005;Dziewit and Drewniak 2016).…”

“…Model examples of enzymatic detoxification systems in bacteria are mercury-and arsenate-resistance mechanisms. The third heavy metal-resistance mechanism involves intracellular sequestration of heavy metals as complexes, by small, cysteine-rich, metal-binding proteins-metallothioneins (Silver and Misra 1988;Silver et al 1989;Nies 2003;Silver and Phung le 2005;Haferburg and Kothe 2007;Blindauer 2011;Dziewit and Drewniak 2016).…”