Regulation of the cadA cadmium resistance determinant of Staphylococcus aureus plasmid pI258

Abstract

Regulation of the cadA cadmium and zinc resistance determinant of Staphylococcus aureus plasmid p1258 was demonstrated by using gene fusions and direct measurements of transcription. In growth experiments, cells harboring the intact cadA operon were induced with different cations and challenged by an inhibitory concentration of ZnC12, a substrate of the CadA resistance system. Uninduced cells did not grow for 8 h after Zn2+ addition, whereas induced cells grew in the presence Zn2+. Cd2" was a strong inducer, and Bi3+ and Pb2+ also induced well; Co2, and Zn2+ were weak inducers. A translational (-lactamase fusion to the cadA gene showed the same induction specificity as that seen with growth experiments with the intact cadA operon. A short j-lactamase transcriptional fusion to the cadC gene also showed the same pattern of induction, establishing that the cadC gene was not involved in regulation. In Northern (RNA) blot hybridization experiments, a cadmium-inducible, 2.6-kb, operon-length transcript was detected. Primer extension experiments determined that Cd2+-inducible transcription of the cad4 operon begins at nucleotides 676 and 677 of the published sequence (G. Nucifora, L. Chu, T. K. Misra, and S. Silver, Proc. Natl. Acad. Sci. USA 86: [3544][3545][3546][3547][3548] 1989).The cadA cadmium resistance determinant of Staphylococcus aureus plasmid pI258 contains two open reading frames (8). The protein products of the cadA efflux ATPase gene (727 amino acids) and of the shorter cadC gene (122 amino acids) have been identified, and the need for both genes for cadmium and zinc resistance has been established in the accompanying paper (24). In the present report, the induction pattern of the cadA operon by various toxic heavy metal cations is described. The cadA cadmium resistance system was previously thought to function constitutively (8,12,20,22) stop sequence, were the gifts of R. P. Novick and were used to construct cadA-blaZ fusions. Cell growth on 2XNY medium, the use of the antibiotics ampicillin (100 ,ug/ml), erythromycin (10 ,ug/ml), and chloramphenicol (5 ,ug/ml), and measurements of growth by turbidity were as described in the accompanying report (24). Cell mass as dry weight was calculated from a curve of dry weight versus turbidity (6).DNA procedures. The manipulation of DNA with enzymes was as described by Sambrook et al. (13). The structure of each fusion was confirmed by nucleotide sequencing by the dideoxynucleotide method (15).Materials. Cadmium chloride, cobalt dichloride, zinc chloride, manganese chloride, lead chloride, and potassium bismuth tartrate were used as cation salts. 5-Bromo-4-chloro-3-indolyl-p-D-galactopyranoside (X-Gal) and isopropyl-p-D-thiogalactopyranoside (IPTG)

A second gene in the Staphylococcus aureus cadA cadmium resistance determinant of plasmid pI258

“…An alternative possibility for the role of the second ORF in gene regulation was eliminated by experiments described in the accompanying paper (36). The results presented here establish that the second ORF is required for full Cd2+ and Zn2+ resistance.…”

Improving the sensitivity of bacterial bioreporters for heavy metals

“…The existence of a Zn-specific sensor element is peculiar, as all of the transcription factors and resistance mechanisms known for Zn 2+ thus far cross-react with Cd 2+ and Pb 2+ (see Table 1). 17,[21][22][23][24] However, as only three sensor elements (the promoters of zntA from E. coli, cadA from P. putida and cadA from S. aureus) have been previously used for the construction of Zn/Cd/Pb-bioreporters, it is still possible that an open-minded search for new heavy-metal-regulated promoters would yield bioreporters with different specificities.…”

Chromosome‐Determined Zinc‐Responsible Operon czr in Staphylococcus aureus Strain 912

“…CzrA was homologous to the SmtB in Synechococcus PCC7942, CadC of pI258 and ArsR of p1258 in S. aureus (13,36,40,44). SmtB, ArsR and CadC contained helix-turn-helix DNA binding motifs and are assumed to be the repressors for smtA (methalothionein), arsABC (arsenate and antimony transport system proteins) and CadA (cadmium transport system), respectively.…”

“…3A) (7). The amino acid sequence for czrA exhibited 34.5% amino acid identities with SmtB in Synechococcus PCC7942, 31.2% CadC of pI258 in S. aureus, and 25.6% ArsR of pI258 in S. aureus (13, 40,44).…”