1999 Volume 43 Issue 2 Pages 115-125
A novel operon, czrAB (zinc-responsible genes), was identified in the chromosome of Staphylococcus aureus. The operon consists of two genes, czrA and czrB. The czrA gene, coding for an 11.5kDa protein, was homologous to cadC, arsR of S. aureus plasmid pI258 and smtB of Synechococcus PCC7942. The czrB, coding for a 36kDa membrane spanning protein, was homologous to the czcD gene, cobalt, zinc and the cadmium -resistant factor of Bacillus subtilis and Alcaligenes eutrophus. In the presence of zinc (0.1-10mM), the transcription of czrAB was enhanced in a concentration-dependent manner. Other heavy metals, such as cobalt, copper, manganese and nickel showed no effect on czrAB expression. The disruptant of the czrB gene became sensitive to zinc ion (MIC, 2mM; MBC, 10mM), and the complementation with the plasmid recovered the resistance to zinc at the same concentration as a parental strain (MIC, 5mM; MBC, 20mM). The disruptant accumulated intracellular zinc up to 0.4mg per g dry weight of the organism, while that of the parental strain was 0.25mg per g dry weight. The findings indicated that the novel operon czrAB should play a role in the transportation of zinc across the cell membrane to maintain the proper intracellular concentration.
