Thèse de doctorat en Sciences biologiques
Sous la direction de Patrick Forterre.
Soutenue en 2007
à Paris 11 , en partenariat avec Université de Paris-Sud. Faculté des sciences d'Orsay (Essonne) (autre partenaire) .
The study of plasmids and viruses has been critical for increasing the knowledge about molecular mechanisms of life. During the last two decades, very different types of viruses have been discovered in hyperthermophilic Archaea from terrestrial hot springs. In order to investigate whether such viral diversity is also found in marine hyperthermophilic Archaea, I have screened and characterized new extra-chromosomal elements from the hyperthermophilic order Thermococcales. I found four new plasmids. The smallest (pTN1) replicates via the rolling circle mechanism, and I have studied the biochemical activities of the two proteins it encodes. Two other plasmids (pTN2 and pP12-1, c. A. 12 kb) belong to a new family characterized by the presence of a gene encoding a putative superfamily I helicase. Some genes of these plasmids also have homologues in Pyrococcus abyssi virus 1 (PAV1) genome. A fourth plasmid (21,6 kb) revealed many homologous genes within integrated elements found in different genomes of euryarchaeotes. I did not find new viruses. However, I have observed that many Thermococcales strains produce vesicles that are sometimes associated with genomic DNA from the host. This work allowed the discovery of new plasmid families in Thermococcales, revealing evolutive relationships with viruses. In other respects, vesicles (sometimes associated with DNA) might protect extra-cellular DNA at high temperatures ; they might be involved in horizontal gene transfers.
Screening and characterization of extra-chromosomal elements from hyperthermophilic Archaea of the order Thermococcales
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