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

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The promiscuous streptococcal plasmid pMV158 replicates via rolling-circle mechanism.
• It possesses two lagging-strand origins, ssoA and ssoU, essential for vegetative replication.
• Plasmid transfer involves conjugative replication and conversion of single-stranded DNA.

Purpose of the Study:

• To investigate the role of lagging-strand origins (ssoA and ssoU) in the horizontal transfer of plasmid pMV158.
• To determine the contribution of each origin to intra- and interspecies plasmid mobilization.

Main Methods:

• Construction of pMV158 derivatives with defects in ssoA, ssoU, or both.
• Testing the mobilization efficiency of these derivatives between different bacterial hosts (Streptococcus pneumoniae and Enterococcus faecalis).

Main Results:

• Both ssoA and ssoU individually supported transfer between Streptococcus pneumoniae strains.
• Efficient mobilization from S. pneumoniae to Enterococcus faecalis required an intact ssoU.
• Plasmids lacking functional ssoU showed significantly reduced interspecies transfer.

Conclusions:

• The lagging-strand origin ssoU is a critical determinant of pMV158 promiscuity.
• A functional sso is essential for efficient plasmid transfer, particularly in interspecies mobilization.
• ssoU plays a key role in the broad host range and horizontal transfer capabilities of pMV158.