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Class 1 integrons are low-cost structures in Escherichia coli
Yohann Lacotte1, Marie-Cécile Ploy1, Sophie Raherison1
1Université de Limoges, INSERM, CHU Limoges, UMR_S 1092, Limoges, France.
The ISME Journal
|April 8, 2017
Summary
Class 1 integrons, which confer antibiotic resistance in bacteria, have a low fitness cost, especially when regulated by the SOS response. Subinhibitory antibiotic concentrations promote the selection of bacteria carrying these low-cost integrons.
Area of Science:
- Microbiology
- Bacterial Genetics
- Evolutionary Biology
Background:
- Resistance integrons are mobile genetic elements that capture and express antibiotic resistance genes.
- Integron maintenance and evolution are poorly understood, despite their clinical significance.
- Integrase (IntI) expression is regulated by the SOS response in E. coli.
Purpose of the Study:
- To assess the fitness cost of class 1 integrons in E. coli.
- To understand the evolutionary dynamics of integron-carrying bacterial populations.
Main Methods:
- Pairwise competition experiments were conducted.
- Fitness costs associated with integrons were evaluated.
- The impact of SOS regulation and gene cassette arrays on fitness was analyzed.
Main Results:
- Class 1 integrons represent low-cost genetic structures.
- The SOS response effectively downregulates costly integrases.
- Integron cost is influenced by the Pc promoter strength, number of gene cassettes, and specific cassette types.
- Subinhibitory antibiotic concentrations select for integron-carrying bacteria, particularly those with strong Pc promoters.
Conclusions:
- Integron regulation by the SOS response minimizes fitness costs.
- The evolution and maintenance of integrons are influenced by gene cassette composition and promoter strength.
- Environmental factors like subinhibitory antibiotics can drive the selection of antibiotic-resistant bacteria harboring integrons.