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Accueil > Actualités

Salle de réunion bat. LWOFF

Lundi 03/11 - 11h00

Marie-Eve Val, Institut Pasteur, Paris.
Title : New insights into the bi-chromosomal organization of the Vibrio cholerae genome

Most bacteria have a single circular chromosome, varying in size from barely 100 kb to over 12 Mb. Bacteria with multiple chromosomes are nonetheless frequent and stably present in several independent taxa. This is the case for numerous pathogens, like Vibrio or Burkholderia, as well as for important symbionts like Rhizobia. Despite their significance, how and why secondary chromosomes arise is currently poorly understood. Current knowledge of bacteria with secondary chromosomes comes primarily from studies in Vibrio cholerae, which harbors two circular chromosomes, a 3 Mbp chromosome one (chr1) and a 1 Mbp chromosome two (chr2). Despite all the gathered information on replication and segregation of chr1 and chr2 in V. cholerae, knowledge of the mechanisms coordinating the maintenance of the two chromosomes is largely incomplete and much remains to be learned about their functional interrelationships. Our approach to tackle these questions is to rationally alter V. cholerae’s genome structure to probe the underlying functionality and regulation of divided chromosomal organization. Construction of a library of synthetic genomic mutants of V. cholerae, coupled to their extensive directed analysis, allows us to progressively draw a comprehensive picture of multipartite bacterial genomes and shed light on the cellular mechanisms coordinating the maintenance of multiple chromosomes. Unexpectedly, this work also resulted in the isolation of spontaneous natural mutants of V. cholerae with a single fused chromosome. The selective advantage of this new genome configuration is enforced by the depletion of the Dam methylase which is essential for chr2 replication