Integrons: Genetic Dynamic Elements in Aeromonas

Abstract

Integrons are genetic elements able to incorporate, express, and exchange cassettes. Cassette exchanges are mediated by an integrase that excises and reinserts them via site-specific recombination between flanking att sequences. Cassettes lack for the most part a promoter, and their excision and reinsertion at the attI site, downstream a Pc promoter, render them transcriptionally active. This work documents the occurrence of complete integrons or parts of them in Aeromonas and examines the dynamics of these elements. Class 1 integrons linked to antibiotic-resistant cassettes were the most abundant in strains isolated from environmental and clinical samples. Detection of class 2 and 3 integrons was infrequent. Only one report of a class 4-like integron in Aeromonas sp. genomospecies paramedia was found, but a search of these integrons in Aeromonas genomes revealed that class 4-like integrons were the second most abundant after those belonging to class 1. In addition to complete integrons, clusters of attC sites lacking a neighboring integron-integrase (CALINs), single attC sites lacking integron-integrase (SALINs), and orphan integrase genes were found in chromosomes, and a low percentage in Aeromonas plasmids. Concerning the integron behavior, it is known to be regulated by SOS response and could be also controlled by host specific factors.