A CHROMOSOMAL ARS OPERON HOMOLOG OF PSEUDOMONAS-AERUGINOSA CONFERS INCREASED RESISTANCE TO ARSENIC AND ANTIMONY IN ESCHERICHIA-COLI

Operons encoding homologous arsenic-resistance determinants (ars) have been discovered in bacterial plasmids from Gram-positive and Gram-neg ative organisms, as well as in the Escherichia coli chromosome. Howeve r, evidence for this arsenic-resistance determinant in the medically a nd environmentally important bacterial species Pseudomonas aeruginosa is conflicting. Here the identification of a P. aeruginosa chromosomal ars operon homologue via cloning and complementation of an E. coli ar s mutant is reported. The P. aeruginosa chromosomal ars operon contain s three potential ORFs encoding proteins with significant sequence sim ilarity to those encoded by the arsR, arsB and arsC genes of the plasm id-based and E. coli chromosomal ars operons. The cloned P. aeruginosa chromosomal ars operon confers augmented resistance to arsenic and an timony oxyanions in an E. coli arsB mutant and in wild-type P. aerugin osa. Expression of the operon was induced by arsenite at the mRNA leve l. DNA sequences homologous with this operon were detected in some, bu t not all, species of the genus Pseudomonas, suggesting that its conse rvation follows their taxonomic-based evolution.