www.landesbioscience.com Mobile Genetic Elements e24774-1 Mobile Genetic Elements 3:2, e24774; March/April 2013; © 2013 Landes Bioscience LEttEr to thE Editor LEttEr to thE Editor

Mobile genetic elements (MGEs) are key players in the emergence and spread of adaptive traits in bacterial populations. When they move horizontally they can provide ready-to-use genes, operons, and even clusters of genes such as integrons, conjugative transposons, and genetic islands already pre-adapted in other strains and species.1 When compared with genome evolution limited to processes within the single cell, primarily driven by the slow accumulation of rare point mutations, dele-tions, and gene-amplification events,2 it is clear that successful acquisition of MGEs can provide giant leaps in bacterial adapta-tion to for example environmental stress-ors. Nowhere is this more evident than the rapid emergence and spread of antibiotic resistance determinants residing on various MGEs in clinically relevant bacterial spe-cies. Yet, with the exception of plasmids,3-6 surprisingly few studies have addressed the impact MGE acquisitions on the popula-tion dynamics of the bacterial host or the subsequent co-evolutionary trajectories following successful transfer events. Such research is important from the perspective of both emergence and reversal of antibi-otic resistance determinants.7,8 One class of MGE’s where data on the effects on the population dynamics of the novel host is limited is the ubiquitous integrons. Costly Class-1 integrons and the domestication of the the functional integras