Conjugative transposons: the tip of the iceberg

Authors

  • Vincent Burrus,

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    • Present address: Division of Geographic Medicine/Infectious Diseases, New England Medical Center and Tuft University School of Medicine, Boston, MA 02111, USA.

  • Guillaume Pavlovic,

    1. Laboratoire de Génétique et Microbiologie, UMR INRA-UHP 1128, IFR110, Faculté des Sciences et Techniques, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
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  • Bernard Decaris,

    1. Laboratoire de Génétique et Microbiologie, UMR INRA-UHP 1128, IFR110, Faculté des Sciences et Techniques, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
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  • Gérard Guédon

    Corresponding authorSearch for more papers by this author

Summary

Elements that excise and integrate, such as prophages, and transfer by conjugation, such as plasmids, have been found in various bacteria. These elements appear to have a diversified set of characteristics including cell-to-cell contact using pili or cell aggregation, transfer of single-stranded or double-stranded DNA, low or high specificity of integration and serine or tyrosine recombinases. This has led to a highly heterogeneous nomenclature, including conjugative transposons, integrative ‘plasmids’, genomic islands and numerous unclassified elements. However, all these elements excise by site-specific recombination, transfer the resulting circular form by conjugation and integrate by recombination between a specific site of this circular form and a site in the genome of their host. Whereas replication of the circular form probably occurs during conjugation, this replication is not involved in the maintenance of the element. In this review, we show that these elements share very similar characteristics and, therefore, we propose to classify them as integrative and conjugative elements (ICEs). These elements evolve by acquisition or exchanges of modules with various transferable elements including at least ICEs and plasmids. The ICEs are probably widespread among the bacteria.

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