Comparative analysis of MOBQ4plasmids demonstrates that MOBQis acis-acting-enriched relaxase protein family

Abstract

ABSTRACTA group of small mobilizable plasmids is increasingly being reported in epidemiology surveys of enterobacteria. Some of them encode colicins, while others are cryptic. All of them encode a relaxase belonging to a previously non-described group of the MOBQclass, MOBQ4. While highly similar in their mobilization module, two families with unrelated replicons can be distinguished, MOBQ41and MOBQ42. Members of both groups were compatible between them and stably maintained inE. coli. MOBQ4plasmids were mobilized by conjugation. They contain two transfer genes,mobAcoding for the MOBQ4relaxase andmobC, which was non-essential but enhanced the plasmid mobilization frequency. The origin of transfer was located between these two divergently transcribedmobgenes. MPFIconjugative plasmids were the most efficient helpers for MOBQ4conjugative transmission. No interference in mobilization was observed when both MOBQ41and MOBQ42were present in the same donor cell. Remarkably, MOBQ4relaxases exhibited acis-acting preference for theiroriTs, a feature already observed in other MOBQplasmids. These findings indicate that MOBQ4plasmids can efficiently spread among enterobacteria aided by coresident IncI1, IncK and IncL/M plasmids, while ensuring their self-dissemination over highly-related elements.IMPORTANCEPlasmids are key vehicles of horizontal gene transfer and contribute greatly to bacterial genome plasticity. A group of plasmids, called mobilizable, is able to disseminate aided by helper conjugative plasmids. Here, we studied a group of phylogenetically-related mobilizable plasmids, MOBQ4, commonly found in clinically-relevant enterobacteria, uncovering the helper plasmids responsible for their dissemination. We found that the two plasmid species encompassed in the MOBQ4group can coexist and transfer orthogonally, despite origin-of-transfer cross-recognition by their relaxases. Specific discrimination among their highly similaroriTsequences is guaranteed by the preferentialcisactivity of the MOBQ4relaxases. Such strategy would be biologically relevant in a scenario of co-residence of non-divergent elements to favor self-dissemination.