Cloning and Expression of cadD , a New Cadmium Resistance Gene of Staphylococcus aureus

Abstract

A cadmium resistance gene, designated cadD, has been identified in and cloned from the Staphylococcus aureusplasmid pRW001. The gene is part of a two-component operon which contains the resistance gene cadD and an inactive regulatory gene, cadX*. A high degree of sequence similarity was observed between cadD and thecadB-like gene from S. lugdunensis, but no significant similarity was found with either cadA orcadB from the S. aureus plasmids pI258 and pII147. The positive regulatory gene cadX* is identical tocadX from pLUG10 over a stretch of 78 codons beginning at the N terminus, but it is truncated at this point and inactive. Sequence analysis showed that the cadmium resistance operon resides on a 3,972-bp element that is flanked by direct repeats of IS257. The expression of cadD in S. aureus and Bacillus subtilis resulted in low-level resistance to cadmium; in contrast, cadA andcadB from S. aureus induced higher level resistance. However, when the truncated version ofcadX contained in pRW001 is complemented intrans with cadX from plasmid pLUG10, resistance increased approximately 10-fold suggesting that the cadmium resistance operons from pRW001 and pLUG10 are evolutionarily related. Moreover, the truncated version ofcadX contained in pRW001 is nonfunctional and may have been generated by deletion during recombination to acquire the cadmium resistance element.

Zn(II) metabolism in prokaryotes

“…Bacterial resistance to Cd(II) is usually based on the efflux of this divalent metal ion and Cd(II) resistance determinants are widespread [175,215–218]. Although the founder members of the growing group of Cd(II) resistance determinants were first identified in S. aureus [198,219,220], plasmid‐borne Cd(II)‐resistant determinants have been more recently identified in Helicobacter pylori [193,203,204,221–223], Staphylococcus lugdunensis [224,225], S. aureus [226,227], P. putida [228], Ralstonia strains (section 1.11.1) and in clinical isolates of L. monocytogenes [216,229,230]. In addition, chromosomally encoded determinants have also been identified in Stenotrophomonas maltophilia [231] and various Pseudomonas species [232,233].…”

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

“…Wildtype S. aureus ATCC12600 tolerate at least 1 mg ml À1 cadmium sulfate, compared to less than 20 mg ml À1 for plasmid-cured S. aureus ATCC12600. This is significantly higher than the tolerance to 150 mg ml À1 cadmium sulfate in S. aureus carrying intact copies of the cadD and cadX genes [13]. It is also higher than the MIC of 256 mM cadmium acetate conferred by pLUG10 in Staphylococcus lugdunensis [14], and the MIC of 12 mM cadmium chloride observed in Streptococcus salivarius 57.I [30].…”

Investigation of the yvgW Bacillus subtilis chromosomal gene involved in Cd2+ ion resistance

“…The results of our study demonstrate that B. subtilis has chromosomally determined resistance to the Cd 2 ions. The cadA gene provides a level of resistance to Cd 2 , which is much lower than the resistance provided by the cadA operon from S. aureus plasmid pI258 after its expression in B. subtilis [7]. A similar rather weak e¡ect has been described for the chromosomal Cd 2 resistance determinant of S. aureus [10].…”

“…The small 122-amino acid CadC protein serves as a positive transcription regulator of the cadmium operon [5,6]. The cadA operon represents one of three known mechanisms of plasmid-mediated cadmium resistance in S. aureus (cadA, cadB and cadD) [1,2,7].…”