Genetic relationship between soxRS and mar loci in promoting multiple antibiotic resistance in Escherichia coli

Abstract

Multiple antibiotic resistance in Escherichia coli has typically been associated with mutations at the mar locus, located at 34 min on the E. coli chromosome. A new mutant, marC, isolated on the basis of a Mar phenotype but which maps to the soxRS (encoding the regulators of the superoxide stress response) locus located at 92 min, is described here. This mutant shares several features with a known constitutive allele of the soxRS gene, prompting the conclusion that it is a highly active allele of this gene. The marC mutation has thus been given the designation soxR201. This new mutant was used to examine the relationship between the mar and sox loci in promoting antibiotic resistance. The results of these studies indicate that full antibiotic resistance resulting from the soxR201 mutation is partially dependent on an intact mar locus and is associated with an increase in the steady-state level of mar-specific mRNA. In addition, paraquat treatment of wild-type cells is shown to increase the level of antibiotic resistance in a dose-dependent manner that requires an intact soxRS locus. Conversely, overexpression of MarA from a multicopy plasmid results in weak activation of a superoxide stress response target gene. These findings are consistent with a model in which the regulatory factors encoded by the marA and soxS genes control the expression of overlapping sets of target genes, with MarA preferentially acting on targets involved with antibiotic resistance and SoxS directed primarily towards components of the superoxide stress response. Furthermore, compounds frequently used to induce the superoxide stress response, including paraquat, menadione, and phenazine methosulfate, differ with respect to the amount of protection provided against them by the antibiotic resistance response.

Identification and analysis of aarP, a transcriptional activator of the 2'-N-acetyltransferase in Providencia stuartii

“…In addition, multiple copies of aarP in E. coli resulted in a threefold increase in the accumulation of ␤-galactosidase from an nfo-lacZ fusion, which is normally activated by the SoxS protein (37). This level of activation is similar to that previously reported for MarA, which was capable of activating an nfo-lacZ fusion twofold (26).…”

“…In contrast, marA is the second member of the three-gene marRAB operon (8). In addition, accumulation of the aarP transcript was not increased by exposure of cells to salicylate, a potent inducer of marA (9,26). Therefore, an alternative possibility is that aarP has a cellular role unrelated to antibiotic resistance but is capable of cross-activating genes in the mar regulon manner similarly to SoxS, presumably as a result of the extensive amino acid identity in the helix-turn-helix regions of AarP and MarA (Fig.…”

“…The chromosomal AmpC ␤-lactamase is under the control of the activator AmpR (23a), and genes involved in multiple antibiotic resistance in Escherichia coli are subject to activation by the MarA (8,16) and SoxS (7,26) proteins. To determine if aac(2Ј)-Ia is also subject to regulation by a positive activator(s), we have initiated a search for plasmids containing random fragments of the P. stuartii chromosome which confer increased aac(2Ј)-Ia expression.…”

Differential Expression of over 60 Chromosomal Genes in Escherichia coli by Constitutive Expression of MarA

“…Our findings provide suggestive evidence for a pu- The exact mechanisms for the overlapping regulation by MarA and SoxS are still poorly understood. Multiple-antibiotic resistance encoded by the soxRS locus appeared partly dependent on an intact mar locus; strains overexpressing SoxS showed increased levels of marRAB transcription (41). On the other hand, other work showed that regulation of some genes by mar and by soxRS can occur through independent pathways, e.g., inaA (46).…”

“…SoxS is the activator of the soxRS regulon (17), which mediates a cellular response to oxidative stress and, like MarA, is a member of the XylS/AraC family of transcriptional activators (20). Many oxidative stress genes, which are known to respond to SoxS, are also responsive to MarA (30,41). Conversely, SoxS is able to confer a Mar phenotype via activation of genes that are under the control of MarA (4,25).…”