Integrons are genetic elements that play an important role in the evolution of bacteria and contribute to the emergence of antibiotic resistant bacterial strains. In their study published last month in NAR (Vit et al., Nucleic Acid Research, 2021 May 28; full-text available here), Dr Celine Loot and colleagues (Bacterial Genome Plasticity team lead by Didier Mazel) performed the first study of cassette integration in the sedentary chromosomal integron of Vibrio cholerae.
They show that cassette integration is efficiently triggered by the endogenous integrase expressed after SOS response induction triggered by the entry of cassettes during horizontal transfer. The cassette insertion events almost exclusively occur at attIA sites where they can be expressed. Vit et al. also present evidence that regulation of cassette integration relies on specific host factors, unlike Mobile Integrons (MI). Escaping the need for host factors may therefore be part of the mechanism that allow the widespread dissemination of MIs in bacteria and explain their impact on the emergence of new antibiotic resistant strains.