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Mol Microbiol. 2010 Nov;78(3):576-88. doi: 10.1111/j.1365-2958.2010.07364.x. Epub 2010 Sep 28.

Integrating conjugative elements of the SXT/R391 family trigger the excision and drive the mobilization of a new class of Vibrio genomic islands.

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1
Centre d'Étude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Université de Sherbrooke, Sherbrooke, QC, Canada.

Abstract

In vibrios and enterobacteria lateral gene transfer is often facilitated by integrating conjugative elements (ICEs) of the SXT/R391 family. SXT/R391 ICEs integrate by site-specific recombination into prfC and transfer by conjugation, a process that is initiated at a specific locus called the origin of transfer (oriT(SXT) ). We identified genomic islands (GIs) harbouring a sequence that shares >63% identity with oriT(SXT) in three species of Vibrio. Unlike SXT/R391 ICEs, these GIs are integrated into a gene coding for a putative stress-induced protein and do not appear to carry any gene coding for a conjugative machinery or for mobilization proteins. Our results show that SXT/R391 ICEs trigger the excision and mediate the conjugative transfer in trans of the three Vibrio GIs at high frequency. GIs' excision is independent of the ICE-encoded recombinase and is controlled by the ICE-encoded transcriptional activator SetCD, which is expressed during the host SOS response. Both mobI and traI, two ICE-borne genes involved in oriT recognition, are essential for GIs' transfer. We also found that SXT/R391 ICEs mobilize in trans over 1 Mb of chromosomal DNA located 5' of the GIs' integration site. Together these results support a novel mechanism of mobilization of GIs by ICEs of the SXT/R391 family.

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