A new route for integron cassette dissemination among bacterial genomes

Abstract

Integrons are genetic elements involved in bacterial adaptation. They can capture, shuffle and express adaptive functions embedded in cassettes. These events are governed by the integron integrase through site-specific recombination between attC and attI integron sites. Here, we demonstrated that the integrase can efficiently catalyze insertion of cassettes in bacterial genomes, outside the att sites. We showed that, once inserted in genomes, cassettes can be expressed, if located near bacterial promoters, and can be excised at the insertion point and even outside, inducing chromosomal modifications in the latter case. Analysis of more than 5 x 105 independent insertion events revealed a very large genomic insertion landscape with recombination sites greatly different, in terms of sequence and structure, from classical att sites. We named these new sites attG. These results unveil a new efficient route for dissemination of adaptive functions and expand the role of integrons in bacterial evolution.