Biology of Spirochetes  


  HEADDr PICARDEAU Mathieu / mpicard@pasteur.fr
  MEMBERSPICARDEAU Mathieu Assistant Professor, PhD / CORNET Murielle Head of the NRCs for Borrelia and Leptospira, MD, PhD / FERQUEL Elisabeth Deputy manager of the NRC for Borrelia, MD / BOURHY Pascale Engineer, PhD Deputy manager of the NRC for Leptospira / BOURGUIGNON Claudia Master 2 student / CRODA Julio PhD student
LAGADEC Quentin Master 2 student / LOUVEL Hélène PhD student / RISTOW Paula PhD student / CHAUMET Delphine Technician / COUEILLE Solange Secretary / MOREL Viviane Technician / GARNIER Martine Technician / SERTOUR Natacha Technician


  Annual Report

Spirochetes are the causative agents of several important animal and human diseases such as Lyme disease and leptospirosis. The unit is composed of a research group on Leptospira and the National Reference Centers for Borrelia and Leptospira (also WHO collaborating Center for Leptospira ).

In 2007, the main research activities included:

i) Comparative genomics between saprophytic and pathogenic Leptospira

In collaboration with the Genomic Platform of the Pasteur Institute, we sequenced the genome of the saprophyte Leptospira biflexa which is our model bacteria. Indeed, numerous tools for genetic manipulation of this saprophytic strain have been developed by our group in the recent years, including random and targeted mutagenesis. We have started the comparison of the genetic content between L. biflexa and pathogenic species that have been already sequenced. Comparative genomics reveals clues on the life-styles of Leptospira in the environment and in the infected host.

ii) Characterization of a genomic island in the pathogen L. interrogans

Comparative genomics of the pathogens L. interrogans serovar Lai and L. interrogans serovar Copenhageni, both belonging to serogroup Icterohaemorrhagiae, revealed a few genetic differences, including a 54-kb genomic island which was only found in serovar Lai. This locus contains a large number of hypothetical ORFs. We successfully amplified a PCR product corresponding to the predicted fragment if the genomic island was excised from the chromosome and its left and right ends joined together. The presence of replication and partition mechanisms typical of circular replicons further confirm that this genomic island can be circularly permuted. This genomic island may confer new phenotypic traits, allowing bacteria to adapt to new environment/host conditions.

iii) Identification of virulence factors in Leptospira

The main objective of the unit is the study of virulence factors in pathogenic strains of Leptospira and the identification of vaccine candidates. Recently, we have demonstrated gene transfer for pathogenic strains of Leptospira using transposition of a transposon of eukaryotic origin. One of the first transposon mutants characterized was a mutant with an insertion into a putative gene encoding a OmpA-domain containing protein. The resulting mutant did not express Loa22 and was attenuated in virulence in the guinea pig and hamster models of leptospirosis, whereas the genetically complemented strain was restored in Loa22 expression and virulence. In addition, our results show that Loa22 was expressed during host infection and exposed on the cell surface. Loa22 is, to our knowledge, the first genetically defined virulence factor in Leptospira species.

iv) Diagnosis and epidemiology of Leptospira and Borrelia

The main objective of the National Reference Centers is to transmit, each year, the epidemiological traits of leptospirosis and Lyme disease to Health authorities. We also have the duty to improve diagnostic techniques. For example, we developed a rapid and simple typing method based on the analysis of the polymorphism of variable-number tandem repeats (VNTR) loci in the genome of the pathogenic species of Leptospira .

Keywords: Spirochetes, Leptospira, Borrelia, epidemiology, genetics, mutagenesis

Spiro.jpg

Electronic microscopy of L. biflexa



  Publications

Bourhy, P., H. Louvel, I. Saint Girons, and M. Picardeau. 2005. Random insertional mutagenesis of Leptospira interrogans, the agent of leptospirosis, using a marinertransposon. J. Bacteriol. 187 :3255-3258. PMID: 15838053

Louvel, H., S. Bommezzadri, N. Zidane, C. Boursaux-Eude,S. Creno, A. Magnier, Z. Rouy, C. Médigue, I. Saint Girons, C. Bouchier, and M. Picardeau. 2006. Comparative and functional genomic analyses of iron transport and regulation in Leptospiraspp. J. Bacteriol. 188:7893-7904. PMID: 16980464

Salaun, L., F. Merien, S. Gurianova, G. Baranton, and M. Picardeau. 2006. Application of multilocus variable-number tandem-repeat analysis for molecular typing of the agent of leptospirosis. J. Clin. Microbiol. 44:3954-3962. PMID: 17088367

Bourhy, P., L. Salaun, A. Lajus, C. Medigue, C. Boursaux-Eude, and M. Picardeau. 2007. A genomic island of the pathogen Leptospira interrogans serovar Lai can excise from its chromosome. Infect. Immun. 75:677-683. PMID: 17118975

Ristow, P., P. Bourhy , F.W. McBride, C.P. Figueira, M. Huerre, P. Ave, I.S. Girons, A.I. Ko, and M. Picardeau. 2007. The OmpA-like protein Loa22 is essential for leptospiral virulence. PLoS Pathog. 3: 0894-0903. PMID: 17630832



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Activity Reports 2007 - Institut Pasteur
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