Cloning and expression of cadD, a new cadmium resistance gene of Staphylococcus aureus

A cadmium resistance gene, designated cadD, has been identified in and clon ed from the Staphylococcus aureus plasmid pRW001, The gene is part of a two -component operon which contains the resistance gene cadD and an inactive r egulatory gene, cadX*. A high degree of sequence similarity was observed be tween cadD and the cadB-like gene from S. lugnunensis, but no significant s imilarity was found with either cadA or cadB from the S, aureus plasmids pI 258 and pII147. The positive regulatory gene cadX* is identical to cadX fro m 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 ca dmium resistance operon resides on a 3,972-bp element that is flanked by di rect repeats of IS257, The expression of cadD in S, aureus and Bacillus sub tilis resulted in low-level resistance to cadmium; in contrast, cadA and ca dB from S, aureus induced higher level resistance. However, when the trunca ted version of cadX contained in pRW001 is complemented in trans with cadX from plasmid pLUG10, resistance increased approximately 10-fold suggesting that the cadmium resistance operons from pRW001 and pLUG10 are evolutionari ly related. Moreover, the truncated version of cadX contained in pRW001 is nonfunctional and may have been generated by deletion during recombination to acquire the cadmium resistance element.