Characterization of the Effects of an rpoC Mutation That Confers Resistance to the Fst Peptide Toxin-Antitoxin System Toxin

Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion SD.
Journal of bacteriology (Impact Factor: 2.81). 10/2012; 195(1). DOI: 10.1128/JB.01597-12
Source: PubMed


Overexpression of the Fst toxin in Enterococcus faecalis strain OG1X leads to defects in chromosome segregation, cell division and, eventually, membrane integrity. The M7 mutant
derivative of OG1X is resistant to most of these effects but shows a slight growth defect in the absence of Fst. Full-genome
sequencing revealed two differences between M7 and its OG1X parent. First, OG1X contains a frameshift mutation that inactivates
the etaR response regulator gene, while M7 is a wild-type revertant for etaR. Second, the M7 mutant contains a missense mutation in the rpoC gene, which encodes the β′ subunit of RNA polymerase. Mutagenesis experiments revealed that the rpoC mutation was primarily responsible for the resistance phenotype. Microarray analysis revealed that a number of transporters
were induced in OG1X when Fst was overexpressed. These transporters were not induced in M7 in response to Fst, and further
experiments indicated that this had a direct protective effect on the mutant cells. Therefore, exposure of cells to Fst appears
to have a cascading effect, first causing membrane stress and then potentiation of these effects by overexpression of certain

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Available from: Roger Bumgarner, Jun 25, 2014
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    • "Differential decay patterns of RNA I and RNA II elicit translation of the former in plasmid-free cells. The toxin disrupts cell membrane function by an as yet unknown mechanism [26]. "
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    ABSTRACT: Multidrug-resistant variants of human pathogens from the genus Enterococcus represent a significant health threat as leading agents of nosocomial infections. The easy acquisition of plasmid-borne genes is intimately involved in the spread of antibiotic resistance in enterococci. Toxin-antitoxin (TA) systems play a major role in both maintenance of mobile genetic elements that specify antibiotic resistance, and in bacterial persistence and virulence. Expression of toxin and antitoxin genes must be in balance as inappropriate levels of toxin can be dangerous to the host. The controlled production of toxin and antitoxin is usually achieved by transcriptional autoregulation of TA operons. One of the most prevalent TA modules in enterococcal species is axe-txe which is detected in a majority of clinical isolates. Here, we demonstrate that the axe-txe cassette presents a complex pattern of gene expression regulation. Axe-Txe cooperatively autorepress expression from a major promoter upstream of the cassette. However, an internal promoter that drives the production of a newly discovered transcript from within axe gene combined with a possible modulation in mRNA stability play important roles in the modulation of Axe:Txe ratio to ensure controlled release of the toxin.
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    • "Over-expression of Fst leads to chromosome condensation and mis-segregation as well as cell division defects (Patel and Weaver, 2006). The precise mechanism of action of the toxin remains undetermined, but recent evidence indicates that lethality might relate to over-expression of transporter proteins (Brinkman et al., 2013). As in many other TA systems, multiple chromosomal homologs of the par system have recently been identified (Weaver et al., 2009b). "
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