A regulatory cascade involving AarG, a putative sensor kinase, controls the expression of the 2′‐N‐acetyltransferase and an intrinsic multiple antibiotic resistance (Mar) response in Providencia stuartii

Abstract

A recessive mutation, aarG1, has been identified that resulted in an 18-fold increase in the expression of beta-galactosidase from an aac(2')-lacZ fusion. Transcriptional fusions and Northern blot analysis demonstrated that the aarG1 allele also resulted in a large increase in the expression of aarP, a gene encoding a transcriptional activator of aac(2')-Ia. The effects of aarG1 on aac(2')-Ia expression were mediated by aarP-dependent and -independent mechanisms. The aarG1 allele also resulted in a multiple antibiotic resistance (Mar) phenotype, which included increased chloramphenicol, tetracycline and fluoroquinolone resistance. This Mar phenotype also resulted from aarP-dependent and -independent mechanisms. Sequence analysis of the aarG locus revealed the presence of two open reading frames, designated aarR and aarG, organized in tandem. The putative AarR protein displayed 75% amino acid identity to the response regulator PhoP, and the AarG protein displayed 57% amino acid identity to the sensor kinase PhoQ. The aarG1 mutation, a C to T substitution, resulted in a threonine to isoleucine substitution at position 279 (T279I) in the putative sensor kinase. The AarG product was functionally similar to PhoQ, as it was able to restore wild-type levels of maganin resistance to a Salmonella typhimurium phoQ mutant. However, expression of the aarP and aac(2')-Ia genes was not significantly affected by the levels of Mg2+ or Ca2+, suggesting that aarG senses a signal other than divalent cations.

The PhoP-PhoQ Two-Component Regulatory System of Photorhabdus luminescens Is Essential for Virulence in Insects

“…(iii) It is possible that PhoPQ is sensitive to other signals present in vivo in the hemocoel. It has been suggested previously that in Erwinia chrysanthemi and Providencia stuartii (42,56) the PhoPQ system may sense chemical signals other than divalent cations. In E. coli, the system has been shown to respond to a mildly acidic pH and acetate in addition to Mg 2ϩ (4,41).…”

The Pleiotropic Two-Component Regulatory System PhoP-PhoQ

“…carotovora (23,24). On the other hand, the PhoQ protein of Providencia stuartii does not appear to respond to Mg 2ϩ but to a yet undefined signal (68).…”

Identification and Characterization of the Point Mutation Which Affects the Transcription Level of the Chromosomal 3- N -Acetyltransferase Gene of Streptomyces griseus SS-1198

“…In contrast, the cloning of the wild-type gene with a high-copy-number vector demonstrated that the wild-type gene could confer a low level (50 g/ml) of Km resistance to S. lividans, suggesting that the difference between resistance levels conferred by the wild-type gene and the mutant genes would be due not to derepression in the heterologous host but to a gene dosage effect. However, we cannot rule out the presence of negative regulators, such as aar factors which regulate the expression of the aac(2Ј)-Ia gene in P. stuartii (21)(22)(23)(24). We have currently found that protoplast regeneration treatment is not necessary for obtaining Km-resistant mutants, because we isolated such mutants without protoplasting (unpublished data).…”