An ompR-envZ Two-Component System Ortholog Regulates Phase Variation, Osmotic Tolerance, Motility, and Virulence in Acinetobacter baumannii Strain AB5075

• Type of Material: Article
• Authors: Kyle A. Tipton, Emory University; Philip Rather, Emory University
• Language: English
• Date: 2017-02-01
• Publisher: American Society for Microbiology
• Publication Version: Final Published Version
• Copyright Statement: © 2017 American Society for Microbiology. All Rights Reserved.
• Final Published Version (URL): http://dx.doi.org/10.1128/JB.00705-16
• Title of Journal or Parent Work: Journal of Bacteriology
• ISSN: 0021-9193
• Volume: 199
• Issue: 3
• Grant/Funding Information: P.N.R. is also supported by grants from the Merit Review program and a Research Career Scientist Award, both from the Department of Veterans Affairs.; This study was funded by grant 1R21AI115183 from the National Institutes of Health and by funds from the Atlanta Research and Education Foundation.
• Keywords: SIGNAL-TRANSDUCTION; MUTANTS; osmotic stress; ESCHERICHIA-COLI K-12; Microbiology; IN-VITRO; PORIN; Life Sciences & Biomedicine; EXPRESSION; RESISTANCE; Acinetobacter; PHOSPHATE; SURFACE-ASSOCIATED MOTILITY; PSEUDOMONAS-AERUGINOSA; Science & Technology; phase variation
• Research Categories: Biology, Microbiology

Abstract

Recently, a novel phase-variable colony opacity phenotype was discovered in Acinetobacter baumannii strain AB5075, where colonies interconvert between opaque and translucent variants. Opaque colonies become mottled or sectored after 24 h of growth due to translucent variants arising within the colony. This easily distinguishable opaque-colony phenotype was used to screen for random transposon insertions that increased the frequency of sectoring at a time point when wild-type colonies were uniformly opaque. A colony was identified that contained multiple papillae of translucent variants, and the insertion in this mutant mapped to an ortholog of the two-component system response regulator ompR. Subsequent investigation of in-frame deletions of ompR and the sensor kinase envZ (located adjacent to ompR) showed that the switching frequency from opaque to translucent was increased 401-and 281-fold, respectively. The ompR mutant also exhibited sensitivity to sodium chloride in growth medium, whereas the envZ mutation did not elicit sensitivity to sodium chloride. Mutation of either gene reduced motility in A. baumannii strain AB5075, but a mutation in both ompR and envZ produced a more profound effect. The ompR and envZ genes were cotranscribed but were not subject to autoregulation by OmpR. Both ompR and envZ mutant opaque variants were attenuated in virulence in the Galleria mellonella infection model, whereas mutation of ompR had no effect on the virulence of the translucent variant.