Why is entry exclusion an essential feature of conjugative plasmids?

Entry exclusion is a property of plasmids by which the cells that contain them become bad recipients in additional conjugation rounds. This work reviews entry exclusion essential features and analyzes the mechanisms of action of the best studied systems. We searched for homologs of the proteins resp...

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Bibliographic Details
Published in:Plasmid 2008-07, Vol.60 (1), p.1-18
Main Authors: Garcillán-Barcia, M. Pilar, de la Cruz, Fernando
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Conjugation inhibition
Conjugation, Genetic - physiology
DNA, Bacterial - genetics
Entry exclusion
Molecular Sequence Data
Plasmid conjugation
Plasmids - chemistry
Plasmids - genetics
Surface exclusion
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Summary:Entry exclusion is a property of plasmids by which the cells that contain them become bad recipients in additional conjugation rounds. This work reviews entry exclusion essential features and analyzes the mechanisms of action of the best studied systems. We searched for homologs of the proteins responsible for experimentally known exclusion systems. Results were used to classify exclusion systems in families of related elements. We arrive to the conclusion that all conjugative plasmids contain at least one entry exclusion gene. Although entry exclusion genes seem to be part of the plasmid conjugative machinery, they are systematically absent in phylogenetically related type IV protein exporting machines involved in virulence for plants and animals. We infer from this fact that entry exclusion is an essential feature of conjugative plasmid biology. Mathematical models suggest that plasmids expressing entry exclusion selectively eliminate plasmids lacking it, reinforcing its essential character and suggesting that entry exclusion plays a direct role in plasmid survival. Other experimental results confirm that entry exclusion is essential for the stability of a conjugative plasmid. We suggest that entry exclusion limits the damage of lethal zygosis (bacterial death produced by excessive rounds of conjugation). Additionally, it avoids competition in a host among identical plasmid backbones. Conversely, the lack of entry exclusion in conjugative transposons can be understood as a means of generating rapid evolutionary change.
ISSN:0147-619X
1095-9890
DOI:10.1016/j.plasmid.2008.03.002