Transposase-Mediated Excision, Conjugative Transfer, and Diversity of ICE Elements in Staphylococcus aureus.

ICE represents one of two families of integrative conjugative elements (ICEs) identified in the pan-genome of the human and animal pathogen Here we investigated the excision and conjugation functions of ICE and further characterized the diversity of this element. ICE excision was not significantly affected by growth, temperature, pH, or UV exposure and did not depend on The IS-like DDE transposase (Tpase; encoded by and ) of ICE must be uninterrupted for excision to occur, whereas disrupting three of the other open reading frames (ORFs) on the element significantly affects the level of excision. We demonstrate that ICE conjugatively transfers to different backgrounds at frequencies approaching that of the conjugative plasmid pGO1. We found that excision is required for conjugation, that not all backgrounds are successful recipients, and that transconjugants acquire the ability to transfer ICE Sequencing of chromosomal integration sites in serially passaged transconjugants revealed a significant integration site preference for a 15-bp AT-rich palindromic consensus sequence, which surrounds the 3-bp target site that is duplicated upon integration. A sequence analysis of ICE from different host strains of and from eight other species of staphylococci identified seven divergent subfamilies of ICE that include sequences previously classified as a transposon, a plasmid, and various ICEs. In summary, these results indicate that the IS-like Tpase functions as the ICE recombinase and that ICE represents a diverse family of mobile genetic elements that mediate conjugation in staphylococci. Integrative conjugative elements (ICEs) encode the abilities to integrate into and excise from bacterial chromosomes and plasmids and mediate conjugation between bacteria. As agents of horizontal gene transfer, ICEs may affect bacterial evolution. ICE represents one of two known families of ICEs in the pathogen , but its core functions of excision and conjugation are not well studied. Here, we show that ICE depends on its IS-like DDE transposase for excision, which is unique among ICEs, and we demonstrate the conjugative transfer and integration site preference of ICE A sequence analysis revealed that ICE has diverged into seven subfamilies that are dispersed among staphylococci.