A DNA fragment conferring resistance to zinc and cobalt ions was
A DNA fragment conferring resistance to zinc and cobalt ions was isolated from a genomic DNA library of RN450. metal ions are toxic in excess of normal physiological levels (28). Increasing environmental concentrations of these heavy metals pose a challenge to bacteria. Therefore, bacteria have evolved mechanisms to regulate the influx and efflux processes to maintain the relatively constant intracellular level of the heavy metal ions. Different molecular mechanisms have been reported that are responsible for resistance to various trace heavy metal ions in bacteria (2, 8, 13, 18, 22, 23, 27). The molecular mechanisms involve a number of proteins, such as ion transporters, reductases, glutathione-related cadystins and cysteine-rich metallothioneins, and low-molecular-weight cysteine-rich metal ligands (27). These protein molecules either export the metal ions out of cells or detoxify or sequester them so that the cells can grow in an environment made up of high levels of toxic metals. However, there is no common mechanism of resistance to all heavy metal ions. In bacteria, the genes encoding resistance to heavy metals are located either around the bacterial chromosome, around the plasmids, or on both (18, 27). is usually a common human pathogen associated with a number of diseases. Understanding of metal resistance in staphylococci has progressed rapidly in the past 10 years, with well-established cadmium, mercury, antimony, and arsenic resistance systems encoded by plasmids (20, 25, 27). However, staphylococcal strains without plasmids show resistance to heavy metal ions, such as zinc and cobalt. This implies that a plasmid-independent chromosomal determinant might encode resistance to heavy metals such as zinc and cobalt. Although operons encoding cobalt, zinc, and cadmium in (17) and zinc in (2) have 114-80-7 IC50 been investigated, relatively little is known about the transport of and resistance mechanisms to zinc 114-80-7 IC50 and cobalt ions in strains were produced on tryptic soy agar or broth (TSA or TSB), whereas strains were produced on Luria-Bertani (LB) agar or broth at 37C with shaking (200 rpm). When necessary for selection, ampicillin (50 g/ml), kanamycin (30 g/ml for was isolated by using DNAzol kits (Molecular Research Center, Inc., Cincinnati, Ohio). Plasmid was purified with the QIAgen plasmid minipreparation kit (Qiagen, Inc., Chatsworth, Calif.). PCR-amplified products and DNA fragments from agarose gels were purified with QIAquick gel extraction kits. DNA probes were labeled by using the Rediprime DNA labeling system (Amersham Life Science, Arlington Heights, Ill.). All DNA restriction and modification enzymes were obtained from Promega (Madison, Wis.) and used according to 114-80-7 IC50 the manufacturers instructions. DNA sequences were decided with an ABI Prism 310 genetic analyzer system (Perkin-Elmer, Foster City, Calif.). Two pairs of oligonucleotide primers were used for PCR amplification: PCA1 and PCA2 (5-TAAAGGCGGCGACACTTCACAC-3 and 5-CTGGTGGTTTTTGCCCAAATTG-3) and CAF1 and CAB1 (5-TTAGATGACATCCACGTAGCAACT-3 and 5-GACCAAACAAGTCGCCATAAAGAC-3). DNA sequences were analyzed by the MacVector (version 5.0) program, and multiple protein alignments were performed by the ClustalW program (29). Construction of the mutant and complementation. The 2 2.9-kb and was cloned into vector pTZ18R. The resulting plasmid pTZ18R-ZC (5.8 kb) was digested with was then subcloned into the pBT2 shuttle vector that contained a temperature-sensitive staphylococcal origin of replication (4). The resulting plasmid pBT2-ZCK was electroporated into qualified RN4220 cells. Selection for double-crossover events with the chromosome of was carried out at 43C FANCD as described previously (3, 4). One representative mutant was analyzed by Southern blotting in order to exclude possible rearrangement adjacent to the insertion sites or a single crossover event by using the 2.9-kb and was cloned into the pCU1 shuttle vector (1). The resulting plasmid, pCU1-ZC, was electroporated into the mutant strain RN-MZ. Analysis of zinc ion accumulation. Zinc concentration was measured as described by Beard et al. (2). Cultures grown overnight were transferred to 40 ml of fresh TSB to give an OD580 of approximately 0.1. When the optical density of cultures came close to 1.0, appropriate amounts of ZnCl2 were added to the cultures.