Costly Class-1 integrons and the domestication of the the functional integrase

Class-1 integrons play an important role in the emergence and spread of antimicrobial resistance determinants. In a recent study we showed that host fitness was dramatically reduced following acquisition of these elements. These fitness costs were due to the presence of an active integrase and we suggested that the mechanistic explanation was due to reduced genetic stability through IntI1 mediated recombination events between attI/attC and non-canonical sites in the chromosome. Here we demonstrate that the attI degenerated target sequence is highly prevalent in our model organism Acinetobacter baylyi adding support to the hypothesis that IntI1 is costly due to genomic instability.