Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Ribosomal proteins can act as oxidative stress sensors in Acinetobacter baumannii (#215)

Uwe H Stroeher 1 , Betty Suryawati 1 , Melissa H Brown 1
  1. Flinders University, Adelaide, SA, Australia

Acinetobacter baumannii is a pathogen that can cause significant hospital borne infections due to its ability to survive environmental stresses. One of these, oxidative stress, was examined under varying zinc availability conditions. The L31 ribosomal protein RpmE1 acts as a major reservoir of zinc through binding this cation to a CxxC motif. During low zinc conditions, RpmE1 is replaced in the ribosome by RmpE2 (which lacks a CxxC zinc-binding motif) allowing for release of zinc that was bound to RmpE1. We constructed two individual deletion mutants (ΔrpmE1 and ΔrpmE2) in A. baumannii ATCC 17978 by gene replacement and examined them phenotypically and transcriptomically. Both strains showed a ~30% reduction in intracellular zinc levels under zinc-deplete conditions, however, in zinc-replete conditions, ΔrpmE1 strains contained more zinc than either ΔrpmE2 or the parent. Subsequent transcriptome profiling of the ΔrpmE1 mutant revealed that the major regulator of zinc homeostasis (zur) was down-regulated, leading to the up-regulation of zinc uptake systems. Cations, including zinc, are known to be protective against oxidative stressors, therefore we examined the ability of the strains to survive and grow under paraquat-induced oxidative stress. Our studies revealed that although ΔrpmE1 cells contain more intracellular zinc they display a higher level of paraquat sensitivity. One possible explanation for this is that the absence of the CxxC zinc-binding motif in ΔrpmE1 cells results in a reduction in their ability to sense oxidative stress. Therefore, RT-PCR was undertaken on parental and ΔrpmE1 cells to analyse expression of genes known to be involved in the oxidative stress response. Compared to the parent, in the ΔrpmE1 background these genes showed lower induction levels during stress. This may explain the increased paraquat sensitivity of ΔrpmE1 cells implying that RmpE1 in A. baumannii is a sensor of oxidative stress.