Abstract
Acinetobacter baumannii is one of the major causes of hard to treat multidrug-resistant hospital infections. A. baumannii features contributing to its spread and persistence in clinical environment are only beginning to be explored. Bacterial toxin-antitoxin (TA) systems are genetic loci shown to be involved in plasmid maintenance and proposed to function as components of stress response networks. Here we present a thorough characterization of type II system of A. baumannii, which is the most ubiquitous TA module present in A. baumannii plasmids. higBA of A. baumannii is a reverse TA (the toxin gene is the first in the operon) and shows little homology to other TA systems of RelE superfamily. It is represented by two variants, which both are functional albeit exhibit strong difference in sequence conservation. The higBA2 operon is found on ubiquitous 11 Kb pAB120 plasmid, conferring carbapenem resistance to clinical A. baumannii isolates and represents a higBA variant that can be found with multiple sequence variations. We show here that higBA2 is capable to confer maintenance of unstable plasmid in Acinetobacter species. HigB2 toxin functions as a ribonuclease and its activity is neutralized by HigA2 antitoxin through formation of an unusually large heterooligomeric complex. Based on the in vivo expression analysis of gfp reporter gene we propose that HigA2 antitoxin and HigBA2 protein complex bind the higBA2 promoter region to downregulate its transcription. We also demonstrate that higBA2 is a stress responsive locus, whose transcription changes in conditions encountered by A. baumannii in clinical environment and within the host. We show elevated expression of higBA2 during stationary phase, under iron deficiency and downregulated expression after antibiotic (rifampicin) treatment.
Highlights
Acinetobacter baumannii is an emerging Gram-negative opportunistic pathogen, causing serious hospital-acquired infections (Antunes et al, 2014)
Further homology search has shown that the closest GP49-domain homologues of HigBAb mentioned in the literature are Mycobacterium tuberculosis Rv2022c-Rv2021c and Rv3182-Rv3183 toxin-antitoxin systems (TAs) systems, whose toxins share more than 40% protein sequence identity with HigBAb (Figure 1A)
The higBAAb module found in plasmid pAB120 (Povilonis et al, 2013), which we characterize in this study, represents the less conservative version higBA2Ab, while the conserved version higBA1Ab has been characterized previously as a representative higBAAb module carried by strain 35 in a pilot study of A. baumannii TA systems (Jurenaite et al, 2013)
Summary
Acinetobacter baumannii is an emerging Gram-negative opportunistic pathogen, causing serious hospital-acquired infections (Antunes et al, 2014). Bacterial type II toxin-antitoxin (TA) systems are the most ubiquitous among six types of prokaryotic toxin-antitoxin systems (TAs), known to date (Chan et al, 2016; Page and Peti, 2016; Rocker and Meinhart, 2016). They are encoded on the low copy plasmids or chromosomes and code for two proteins, one of which (toxin) is toxic to the cell, whereas the other (antitoxin) neutralizes its toxicity by forming strong protein– protein complex, which is non-harmful. The TA systems can adjust the metabolic processes at a large scale, such as shutting down protein synthesis and switching to a dormant cellular state (Kedzierska and Hayes, 2016; Lee and Lee, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
