Chromosomal Integrons are Genetically and Functionally Isolated Units of Genomes

Abstract

Integrons are genetic elements that increase the evolvability of bacteria by capturing new genes and stockpiling them in arrays. Sedentary chromosomal integrons (SCIs), can be massive and highly stabilized structures encoding hundreds of genes, whose function remains generally unknown. SCIs have co-evolved with the host for aeons and are highly intertwined with their physiology from a mechanistic point of view. But, paradoxically, other aspects, like their variable content and location within the genome, suggest a high genetic and functional independence. In this work, we have explored the connection of SCIs to their host genome using as a model the Superintegron (SI), a 179-cassette long SCI in the genome ofVibrio choleraeN16961. We have relocated and deleted the SI using SeqDelTA, a novel method that allows to counteract the strong stabilization conferred by toxin-antitoxin systems within the array. We have characterized in depth the impact inV. cholerae’sphysiology, measuring fitness, chromosome replication dynamics, persistence, transcriptomics, phenomics and virulence. The deletion of the SI did not produce detectable effects in any condition, proving that -despite millions of years of co-evolution-, SCIs are genetically and functionally isolated units of genomes.

Mobile Integrons Encode Phage Defense Systems

“…An extreme case of this is shown by Darracq et al in a back-to-back paper in this issue, where they describe the presence of PICs in the Superintegron of Vibrio cholerae. Indeed, in a recent work we have shown that the Superintegron is carried at no measurable cost 59 . Additionally, their findings proves that chromosomal integrons are virtually infinite repositories of PICs from where they can be recollected by mobile integrons.…”