title: Class 1 integrons are low-cost structures in Escherichia coli.
abstract: Resistance integrons are bacterial genetic platforms that can capture and express antibiotic resistance genes embedded within gene cassettes. The capture and shuffling of gene cassettes are mediated by the integrase IntI, the expression of which is regulated by the SOS response in Escherichia coli. Gene cassettes are expressed from a common Pc promoter. Despite the clinical and environmental relevance of integrons, the selective forces responsible for their evolution and maintenance are poorly understood. Here, we conducted pairwise competition experiments in order to assess the fitness cost of class 1 integrons in E. coli. We found that integrons are low-cost structures and that their cost is further reduced by their tight regulation. We show that the SOS response prevents the expression of costly integrases whose cost is activity dependent. Thus, when an integron is repressed, its cost depends mostly on the expression of its gene cassettes array and increases with Pc strength and the number of cassettes in the array. Furthermore, different cassettes have different costs. Lastly, we showed that subinhibitory antibiotic concentrations promoted the selection of integron-carrying bacteria, especially those with a strong Pc promoter. These results provide new insights into the evolutionary dynamics of integron-carrying bacterial populations.
authors.affiliation: Université de Limoges, INSERM, CHU Limoges, UMR_S 1092, Limoges, France.
authors.forename: Yohann
authors.initials: Y
authors.lastname: Lacotte
authors.affiliation: Université de Limoges, INSERM, CHU Limoges, UMR_S 1092, Limoges, France.
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Ploy
authors.affiliation: Université de Limoges, INSERM, CHU Limoges, UMR_S 1092, Limoges, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Raherison
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D005075:Biological Evolution; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D019426:Integrases / Q000235:genetics; D032023:Integrons / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic; D013014:SOS Response, Genetics / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D019426:Integrases