Prevalence of SOS-mediated control of integron integrase expression as an adaptive trait of chromosomal and mobile integrons
Mobile DNA publish this investigation article
April 30th, 2011
BACKGROUND: Integrons are found in hundreds of environmental bacterial species, but are mainly known as the agents responsible for the capture and spread of antibiotic resistance determinants among Gram-negative pathogens. The SOS response is a regulatory network under control of the repressor protein LexA targeted at addressing DNA damage, thus promoting genetic variation in times of stress. We recently reported a direct link between the SOS response and the expression of integron integrases in Vibrio cholerae and a plasmid-borne class 1 mobile integron. SOS regulation enhances cassette swapping and capture in stressful conditions, while freezing the integron in steady environments. We conducted a systematic study of available integron integrase promoter sequences to analyze the extent of this relationship across the Bacteria domain.
RESULTS: Our results showed that LexA controls the expression of a large fraction of integron integrases by binding to Escherichia coli-like LexA binding sites. In addition, the results provide experimental validation of LexA control of the integrase gene for another Vibrio chromosomal integron and for a multiresistance plasmid harboring two integrons. There was a significant correlation between lack of LexA control and predicted inactivation of integrase genes, even though experimental evidence also indicates that LexA regulation may be lost to enhance expression of integron cassettes.
CONCLUSIONS: Ancestral state reconstruction on an integron integrase phylogeny leads us to conclude that the ancestral integron was already regulated by LexA. The data also indicates that SOS regulation has been actively preserved in mobile integrons and large chromosomal integrons, suggesting that unregulated integrase activity is selected against. Nonetheless, additional adaptations have probably arisen to cope with unregulated integrase activity. Identifying them may be fundamental in deciphering the uneven distribution of integrons in the Bacteria domain
Cambray G., Sanchez-Alberola N., Campoy S., Guerin E., Da Re S., Gonzalez-Zorn B., Ploy MC., Barbe J., Mazel D. and Erill I.
 | Servicio de Zoonosis de Transmisión Alimentaria y Resistencia a Antimicrobianos (ZTA). Centro de Vigilancia Sanitaria Veterinaria (VISAVET). Universidad Complutense (UCM). |
| Departamento de Sanidad Animal. Facultad de Veterinaria. Universidad Complutense (UCM). |
 | Bacterial Genome Plasticity (BGP). Department of Genomes and Genetics. Institut Pasteur. |
| Department of Biological Sciences. University of Maryland Baltimore County (UMBC). | |
 | Faculté de Médecine. Université de Limoges (UL). |
 | Departament de Genčtica i de Microbiologia. Universitat Autňnoma de Barcelona (UAB). |
