Significance Of Metal Resistance Genes

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In microorganisms metal resistance character is regulated by genes which are organized in operons. Commonly, the heavy metal resistance genes are found on plasmid carried by metal resistant bacteria. In the presence of specific metals in the vicinity of bacterial niche the heavy metal resistance genes are expressed and induced. The regulation of expression of metal resistant gene is specific for each heavy metal and is dependent upon metal species concentration. The promoter and regulator genes of the bacterial operons responsible for resistance property and can be used to form metal-specific biosensors. Bacterial sensors which are metal specific coupled with tools for chemical analyses and can be used for differentiation of the concentration …show more content…
In Gram negative bacteria cadmium is targeted on DsbA gene in the periplasm. DsbA gene is responsible for the formation of disulfide. Cadmium resistance in some gram-positive bacteria was also found to be mediated by CadA-like proteins (Liu et al., 1997). In S. cerevisiae, cadmium is bound by glutathione, and the resulting cadmium-bis-glutathione to complex is transported by an ABC transporter the YCF1p transporter, into the vacuole (Li et al., 1996; Li et al., 1997). This may be a general principle in all eukaryotes. The multidrug-resistance-associated protein from man may complement YCF1 mutation with respect to cadmium resistance (Tommasini et al., 1996). In cyanobacteria transport may also be necessary for cadmium resistance because it contains various types of RNA- and P-type transport systems. Ncc, a nickel exporter (Schmidt and Schlegel 1994) and RND-driven systems like Czc a zinc exporter [53-54 Nies, 1995; Nies 1989b) present in gram-negative bacteria, and involved in detoxification of …show more content…
Cadmium binds with the glutathione and the sulfhydryl groups of proteins and disturbs the cysteine biosynthesis pathway and protein function (Nies, 1999; Helbig et al., 1978) and cadmium is also responsible for DNA damaging (Mitra and Bernstein, 1978; Badisa et al., 2007). Different bacteria used different types of resistance mechanisms for cadmium such methods are metal exclusion by reduced membrane permeability, intra- or extracellular sequestration or active export (Bruins et al., 2000; Wang et al., 2010). Out of these different mechanisms active export is the main mechanism in cadmium tolerant bacteria. CadA (Smith and Novick, 1972; Nucifora et al., 1989), Ncc (also exporting cobalt and nickel) (Schmidt and Schlegel, 1994), Czc (also exporting cobalt and zinc) (Nies 1995), and CzcP Scherer and (Nies, 2009) are the four active export systems that are reported in resistance mechanisms of bacteria. In Gram negative bacteria CzcP and Ncc were found and worked as the main heavy metal export system, and the P1-type ATPase CadA, was firstly identified in Staphylococcus aureus, Listeria and Lactococcus species (Lebrun et al., 1994; Bal et al., 2003), worked as the ‘efflux system of Gram-positive bacteria’ (Silver and Phung, 1996). CadA exporter not only works in resistance to cadmium but also to high concentrations of zinc and lead and expression of CadA is induced

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