Functional characterization of a cadmium resistance operon in Staphylococcus aureus ATCC12600: CadC does not function as a repressor

Abstract

Sequencing of a cadmium resistance operon from a Staphylococcus aureus ATCC12600 plasmid revealed that it is identical to a cadCA operon found in MRSA strains. Compared to plasmid-cured and cadC-mutant strains, cadC-positive ATCC12600 cells had increased resistance to cadmium (1 mg ml À1 cadmium sulfate) and zinc (4 mg ml À1 zinc sulfate), but not to other metal ions. After growth in media containing 20 mg ml À1 cadmium sulfate, cadC-mutant cells contained more intracellular cadmium than cadC-positive ATCC12600 cells, suggesting that cadC absence results in impaired cadmium efflux. Electrophoretic mobility shift assays were performed with CadC proteins encoded by the S. aureus ATCC12600 plasmid and by the cadC gene of pI258, which is known to act as a transcriptional repressor and shares only 47% protein sequence identity with ATCC12600 CadC. Mobility shifts occurred when pI258 CadC protein was incubated with the promoter DNA-regions from the pI258 and S. aureus ATCC12600 cadCA operons, but did not occur with S. aureus ATCC12600 CadC protein, indicating that the ATCC12600 CadC protein does not interact with promoter region DNA. This cadCA operon, found in MRSA strains and previously functionally uncharacterized, increases resistance to cadmium and zinc by an efflux mechanism, and CadC does not function as a transcriptional repressor.

Supramolecular Kandinsky circles with high antibacterial activity

“…Such ‘synergistic’ effects are of interest as they may help circumvent resistance and reduce the toxicity of conventional antibiotics. Indeed, the resistance of MRSA to cadmium salts can be >1 mg/mL 48 , much higher than the MIC of G2−G4 . We speculated that the toxicity of Cd(II) ions could be substantially reduced in the coordination with multi-armed tpy ligands, which act as the chelation agent like EDTA used in the standard chelation therapy for Cd(II).…”

Minicells as an Escherichia coli mechanism for the accumulation and disposal of fluorescent cadmium sulphide nanoparticles

“…In E. coli the ATP-dependent transporter ZntA releases zinc and cadmium to the periplasmic space for subsequent excretion [ 20 , 54 , 55 ]. Additionally, CadA functions as an efflux ATPase, regulating the intracellular levels of cadmium and other metals, and is regulated by the cadmium-binding proteins CadR in Pseudomonas putida [ 56 ] and CadC in Staphylococcus aureus [ 57 ]. Sequestration of heavy metals inside the cell is another strategy involving adsorption by cell-produced molecules like metallothioneins, peptides rich in cysteine capable of trapping metal ions [ 58 – 60 ].…”

Determinantes Genéticos Y Sus Mecanismos De Acción Implicados en La Resistencia Bacteriana a Metales Pesados: Una Revisión.

“…El sistema de resistencia al cadmio en las bacterias Gram positivas es el sistema cad, se ha identificado el conjunto de genes cadCA en S. aureus ATCC12600 aislado de un ambiente hospitalario, en Bacillus vietamensis 151-6 y Bacillus marisflavi 151-25 aisladas de un suelo contaminado con cadmio (64,65,66,67). Por otro lado, en el genoma de la cepa JMAK1 de Bacillaceae aislada de la estación Concordia de la Antártica, se ha evidenciado la presencia de los genes cadA, cadC y cadD (68).…”

“…El gen cadC codifica para el represor CadC que se disocia del operador/promotor de cad tras la unión de Cd 2+ (65). CadC de la cepa ATCC12600 presenta dos sitios de unión al metal (64). Por el contrario, CadC de Listeria monocytogenes EGDe, carece del sitio de tipo II.…”