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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
Author(s) -
Rather Philip N.,
Paradise Michael R.,
Parojcic Milica M.,
Patel Shilpa
Publication year - 1998
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1998.00900.x
Subject(s) - biology , genetics , gene , response regulator , microbiology and biotechnology , mutant , activator (genetics) , peptide sequence , wild type
A recessive mutation, aarG1 , has been identified that resulted in an 18‐fold increase in the expression of β‐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 Mg 2+ or Ca 2+ , suggesting that aarG senses a signal other than divalent cations.