Bringing them together: plasmid pMV158 rolling circle replication and conjugation under an evolutionary perspective
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Published on: December 14, 2019
Fabián Lorenzo-Díaz1, Cris Fernández-López2, M Pilar Garcillán-Barcia3
1Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria and Instituto Universitario de Enfermedades Tropicales y Salud Pública de Canarias, Centro de Investigaciones Biomédicas de Canarias, Universidad de La Laguna, Santa Cruz de Tenerife, Spain.
Abstract:
Rolling circle-replicating plasmids constitute a vast family that is particularly abundant in, but not exclusive of, Gram-positive bacteria. These plasmids are constructed as cassettes that harbor genes involved in replication and its control, mobilization, resistance determinants and one or two origins of lagging strand synthesis. Any given plasmid may contain all, some, or just only the replication cassette. We discuss here the family of the promiscuous streptococcal plasmid pMV158, with emphasis on its mobilization functions: the product of the mobM gene, prototype of the MOBV relaxase family, and its cognate origin of transfer, oriT. Amongst the subfamily of MOBV1 plasmids, three groups of oriT sequences, represented by plasmids pMV158, pT181, and p1414 were identified. In the same subfamily, we found four types of single-strand origins, namely ssoA, ssoU, ssoW, and ssoT. We found that plasmids of the rolling-circle Rep_2 family (to which pMV158 belongs) are more frequently found in Lactobacillales than in any other bacterial order, whereas Rep_1 initiators seemed to prefer hosts included in the Bacillales order. In parallel, MOBV1 relaxases associated with Rep_2 initiators tended to cluster separately from those linked to Rep_1 plasmids. The updated inventory of MOBV1 plasmids still contains exclusively mobilizable elements, since no genes associated with conjugative transfer (other than the relaxase) were detected. These plasmids proved to have a great plasticity at using a wide variety of conjugative apparatuses. The promiscuous recognition of non-cognate oriT sequences and the role of replication origins for lagging-strand origin in the host range of these plasmids are also discussed.
Insights
Rolling circle plasmids, abundant in Gram-positive bacteria, possess diverse replication and mobilization genes. This study details the pMV158 plasmid family, revealing distinct origin of transfer and single-strand origin types, influencing bacterial host range.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Rolling circle-replicating plasmids are prevalent in Gram-positive bacteria, carrying essential genes for replication, control, mobilization, and DNA synthesis.
- The streptococcal plasmid pMV158 serves as a model for studying promiscuous plasmid families, particularly their mobilization mechanisms.
Purpose of the Study:
- To analyze the mobilization functions of the pMV158 plasmid family, focusing on the MOBV relaxase and its origin of transfer (oriT).
- To investigate the diversity of origin of transfer (oriT) and single-strand origin (sso) sequences within the MOBV1 plasmid subfamily.
- To explore the association between rolling-circle replication initiator families (Rep_1 and Rep_2) and their preferred bacterial hosts, as well as their link to MOBV1 relaxases.
Main Methods:
- Comparative analysis of plasmid sequences to identify and classify oriT and sso types.
- Phylogenetic analysis of MOBV1 relaxases and replication initiator proteins.
- Bioinformatic assessment of plasmid distribution across bacterial orders.
Main Results:
- Three distinct oriT sequence groups (pMV158, pT181, p1414) and four sso types (ssoA, ssoU, ssoW, ssoT) were identified within the MOBV1 subfamily.
- Plasmids with Rep_2 initiators are more common in Lactobacillales, while Rep_1 initiators favor Bacillales.
- MOBV1 relaxases associated with Rep_2 initiators show distinct clustering compared to those linked with Rep_1 plasmids.
- MOBV1 plasmids are mobilizable and exhibit broad host range plasticity by utilizing various conjugative systems.
Conclusions:
- The study clarifies the diversity of mobilization and replication origins in rolling circle plasmids.
- Host range plasticity is influenced by the promiscuous recognition of oriT sequences and replication origins.
- MOBV1 plasmids are exclusively mobilizable, relying on diverse conjugative apparatuses for transfer.
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