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J. Bacteriol. doi:10.1128/JB.01257-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Lagging strand DNA replication origins are required for conjugal transfer of the promiscuous plasmid pMV158

Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9. E-28040 Madrid, Spain

^* To whom correspondence should be addressed. Email: mespinosa{at}cib.csic.es.

	Abstract

The promiscuous streptococcal plasmid pMV158 is mobilizable by auxiliary plasmids and replicates by the rolling circle mechanism in a variety of bacterial hosts. The plasmid has two lagging strand origins, ssoA and ssoU, involved in the conversion of single stranded DNA intermediates into double stranded plasmid DNA during vegetative replication. Transfer of the plasmid also would involve conversion of single-stranded DNA molecules into double-stranded plasmid forms in the recipient cells by conjugative replication. To test whether lagging-strand origins played a role in horizontal transfer, pMV158-derivatives defective in one or in both sso were constructed and tested for their ability to colonize new hosts by means of intra- and inter-species mobilization. Whereas either sso supported transfer between strains of Streptococcus pneumoniae, only those plasmids that had an intact ssoU could be efficiently mobilized from S. pneumoniae to Enterococcus faecalis. Thus, it appears that ssoU is a critical factor for pMV158 promiscuity and that the presence of a functional sso plays an essential role in plasmid transfer.