Activation of phenotypic subpopulations in response to ciprofloxacin treatment in Acinetobacter baumannii
Ashley E Macguire1, Meining Carly Ching, Brett H Diamond
1Department of Biology, Northeastern University, Boston, Massachusetts, USA.
Abstract:
The multidrug-resistant, opportunistic pathogen, Acinetobacter baumannii, has spread swiftly through hospitals worldwide. Previously, we demonstrated that A. baumannii regulates the expression of various genes in response to DNA damage. Some of these regulated genes, especially those encoding the multiple error-prone DNA polymerases, can be implicated in induced mutagenesis, leading to antibiotic resistance. Here, we further explore the DNA damage-inducible system at the single cell level using chromosomal transcriptional reporters for selected DNA damage response genes. We found the genes examined respond in a bimodal fashion to ciprofloxacin treatment, forming two phenotypic subpopulations: induced and uninduced. This bimodal response to ciprofloxacin treatment in A. baumannii is unique and quite different than the Escherichia coli paradigm. The subpopulations are not genetically different, with each subpopulation returning to a starting state and differentiating with repeated treatment. We then identified a palindromic motif upstream of certain DNA damage response genes, and have shown alterations to this sequence to diminish the bimodal induction in response to DNA damaging treatment. Lastly, we are able to show a biological advantage for a bimodal response, finding that one subpopulation survives ciprofloxacin treatment better than the other.
Insights
Acinetobacter baumannii exhibits a unique bimodal response to DNA damage, creating distinct subpopulations with varying survival rates. This finding offers insights into antibiotic resistance mechanisms in this opportunistic pathogen.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Acinetobacter baumannii is a multidrug-resistant pathogen causing hospital-acquired infections.
- This bacterium regulates gene expression in response to DNA damage, potentially influencing antibiotic resistance.
- Previous work showed DNA damage response in A. baumannii, but the single-cell dynamics were unexplored.
Purpose of the Study:
- To investigate the DNA damage-inducible system in Acinetobacter baumannii at the single-cell level.
- To characterize the unique response of A. baumannii to DNA damaging agents like ciprofloxacin.
- To identify genetic elements and biological advantages associated with this response.
Main Methods:
- Utilized chromosomal transcriptional reporters to monitor DNA damage response genes in single cells.
- Analyzed gene expression patterns in response to ciprofloxacin treatment.
- Identified and manipulated a palindromic DNA motif upstream of response genes.
- Assessed survival rates of different subpopulations under ciprofloxacin exposure.
Main Results:
- Acinetobacter baumannii displays a bimodal response to ciprofloxacin, forming induced and uninduced subpopulations.
- This bimodal response is genetically identical within subpopulations and reversible.
- A specific palindromic motif was identified as crucial for the bimodal induction.
- One subpopulation demonstrated enhanced survival during ciprofloxacin treatment, indicating a biological advantage.
Conclusions:
- The bimodal DNA damage response in A. baumannii is a novel phenomenon distinct from other bacteria like E. coli.
- This response, regulated by a specific DNA motif, provides a survival advantage against antibiotics.
- Understanding this system is critical for developing new strategies against Acinetobacter baumannii infections.
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