Transfert, accrétion et mobilisation des éléments intégratifs conjugatifs et des îlots génomiques apparentés de "Streptococcus termophilus" : Un mécanisme clef de l'évolution bactérienne ?

Abstract : Analyses of genomes had suggested that numerous bacterial genomic islands would be integrative conjugative elements (ICEs) or elements deriving from them. ICEs excise under a circular form by site-specific recombination, transfer by conjugation, and integrate in a recipient cell. The type of elements is very widespread in genomes of bacteria and archaea. Various related genomic islands are integrated at the 3' of the fda ORF in different Streptococcus thermophilus strains. This family includes 2 integrative and potentially conjugative elements, of which ICESt3, and 4 elements deriving from ICEs by deletion and named CIMEs (cis mobilizable elements). This work has demonstrated that ICESt3 transfers between S. thermophilus and related species. This element is the first conjugative element identified in this streptococcus. The ICESt3 transfer to a cell already carrying an ICE or a CIME leads to the characterization of site-specific accretions of ICESt3 and a related genomic island. Using donor cell harboring a CIME-ICE tandem, the co-transfer of the CIME and the ICE, the transfer of the ICE and the transfer of the only CIME were obtained, demonstrating conjugative mobilization of a CIME by ICESt3. Thus, the genomic islands from S. thermophilus evolve by site-specific accretion and conjugative mobilization. Moreover, an analysis of sequences from databases and an analysis of literature strongly suggest that CIMEs are widespread and that site-specific accretions between genomic islands play a key role in bacterial evolution.
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Xavier Bellanger. Transfert, accrétion et mobilisation des éléments intégratifs conjugatifs et des îlots génomiques apparentés de "Streptococcus termophilus" : Un mécanisme clef de l'évolution bactérienne ?. Génomique, Transcriptomique et Protéomique [q-bio.GN]. Université Henri Poincaré - Nancy 1, 2009. Français. ⟨NNT : 2009NAN10125⟩. ⟨tel-01748335⟩

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