Abstract
Sub-inhibitory concentrations (sub-MIC) of antibiotics play a very important role in selection and development of resistances. Unlike Escherichia coli, Vibrio cholerae induces its SOS response in presence of sub-MIC aminoglycosides. A role for oxidized guanine residues was observed, but the mechanisms of this induction remained unclear. To select for V. cholerae mutants that do not induce low aminoglycoside-mediated SOS induction, we developed a genetic screen that renders induction of SOS lethal. We identified genes involved in this pathway using two strategies, inactivation by transposition and gene overexpression. Interestingly, we obtained mutants inactivated for the expression of proteins known to destabilize the RNA polymerase complex. Reconstruction of the corresponding mutants confirmed their specific involvement in induction of SOS by low aminoglycoside concentrations. We propose that DNA lesions formed on aminoglycoside treatment are repaired through the formation of single-stranded DNA intermediates, inducing SOS. Inactivation of functions that dislodge RNA polymerase leads to prolonged stalling on these lesions, which hampers SOS induction and repair and reduces viability under antibiotic stress. The importance of these mechanisms is illustrated by a reduction of aminoglycoside sub-MIC. Our results point to a central role for transcription blocking at DNA lesions in SOS induction, so far underestimated.
Highlights
Vibrio cholerae is a human pathogen that grows planktonically or as biofilms on crustacean shells, where it couples genome plasticity and adaptation to a changing environment, through the modulation of the SOS response
We previously studied the effect of sub-minimal inhibitory concentrations of antibiotics from different structural families on induction of the SOS response in V. cholerae and Escherichia coli
To gain further insight into mechanisms connecting AG treatment and the SOS response in V. cholerae, we developed a genetic screen to select for V. cholerae mutants that do not induce the SOS response upon exposure to sub-MIC AGs but that are still capable of inducing it in other conditions
Summary
Vibrio cholerae is a human pathogen that grows planktonically or as biofilms on crustacean shells, where it couples genome plasticity and adaptation to a changing environment, through the modulation of the SOS response. Sub-MICs of antibiotics are commonly found in various environments due to the increased production and use of antibiotics for the treatment of humans and animals. Their presence in the environment [4,5,6,7] can be a potent stressor for bacteria and likely plays a very important role for selection of resistances [8]. We observed that sub-MICs of aminoglycosides (AGs) induce the SOS response in V. cholerae but not in E. coli [9] This observation was interesting, as AGs do not target DNA but rather affect translation. We obtained evidence showing that low AG concentrations induce the incorporation of oxidized guanine (8-oxo-G) residues from the dNTP
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