Dual Regulation of inaA by the Multiple Antibiotic Resistance (Mar) and Superoxide (SoxRS) Stress Response Systems of Escherichia coli
The roles of the marR4B (multiple antibiotic resistance) operon and soxRS (superoxide response) genes in the regulation ofinaA, an unliked weak-acid-inducible gene, were studied. inA expression was estimated ftom the P-galactosidase activity of a chromosomal iawA::lcZ transcriptional fusion. marR mutations that elevate marRAB transcription and engender multiple antibiotic resistance elevated inaA4 expression by 10- to 20fold over that of the wild-type. Similarly, one class of ina4 constitutive mutants that mapped to the mar region were multiply antibiotic resistant. Overexpression of marA alone on a multicopy plasmid caused hgh constitutive expression of iAa4 in a strain with an extensive (39-kbp) marR4B deletion. Salicylate, an inducer of marRAB and of an unidentified mar-independent antibiotic resistance system, induced ina4 by 6.fold. A portion of this induction was also mar independent Two sokRS constitutive mutants that were tested showed elevated levels of inaA. Paraquat, an inducer of the soxRS system, elevated GaeA expression by 6- to 9-fold. This induction was soxRS dependent and not mar dependent, whereas induction of ina4 by salicylate was not dependent on saxRS. Paraquat induced resistance to norfioxacin In the mar-deleted strain but not in a soxRS-deleted strain. Thus, induction of multiple antibiotic resistance and inaA by salicylate occurs via mar and an unidentified pathway, while induction by paraquat occurs via soxRS.
Journal of Bacteriology