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Presentation of the laboratory and its research topics:
Leptospira spp. belong to the phylum of spirochetes. This phylum includes saprophytes as well as pathogens species which are responsible for the widespread zoonotic disease leptospirosis. The clinical manifestations of this infection range from flu-like symptoms to kidney failure and pulmonary hemorrhage and more than one million cases are estimated to occur each year. Leptospira are understudied bacteria and their basic biology is largely unknown.
Our laboratory is interested in identifying virulence factors of Leptospira and to study the basic physiology of Leptospira spp. We employ a combination of genetics, basic microbiology, biochemistry and structural biology to explore the mechanism whereby Leptospira infect, colonize and survive inside their mammalian hosts.
Our laboratory also hosts the National Reference Center and WHO Collaborating Center for Leptospirosis devoted to the surveillance of the disease in mainland France and french overseas territories. We develop and improve new tools for leptospirosis diagnosis and we identify Leptospira strains allowing to study the epidemiology of this disease.
Description of the project:
(1 page, Arial font size 11 : 600 words in total with at least 50% dedicated specifically to the PhD project(s))
Leptospira spp. exhibit unique and fascinating morphological features. They are thin, helical and highly motile bacteria. Like classical Gram-negative bacteria, Leptospira have a double-membrane envelope structure, but the outer membrane is rich in surface exposed lipoproteins and the lipid A constituting their LPS is unique. Their motility is driven by two endoflagella located in the periplasmic space.
The Leptospira pathogenic strains are slow growing organisms with an in vitro doubling time of about 20 hours and targeted mutagenesis is still a challenge in these species. However, the saprophyte L. biflexa has a faster growth (doubling time of 5 hours) and a more efficient mutagenesis. Therefore, the saprophyte strain is often used as a model organism to study the basic biology of Leptospira.
The current understanding of their virulence mechanism and general physiology remains unknown. The aim of this PhD project is to determine the mechanisms used by pathogenic strains to colonize and survive inside the host environment.
The difficulty of targeted gene inactivation has hampered the identification of virulence factors of Leptospira. Our laboratory has developed genetic tools to generate random transposon mutant libraries in the pathogen strain L. interrogans and we are constantly increasing the number of mutants constituting the L. interrogans mutant library. One aim of this project will be to search the library for mutants impaired in virulence. Mutants inactivated in putative virulence factors will be used in infection of animal models. Once identified, these mutants will be further characterized for ability to survive in different conditions in vitro, especially those encountered inside a host. The virulence factor inactivated in the mutants will be characterized at biochemical and structural levels.
We have already identified several factors involved in Leptospira virulence including the heat shock proteins ClpB and Hsp90, a catalase responsible for peroxyde detoxification, flagellar proteins essential for Leptospira motility, and Leucine-Rich Repeat (LRRs) containing proteins generally involved in interaction with host cells. Other important pathways such as regulation of oxydative stress and iron uptake and metabolism are also studied in our laboratory. Another aim of this project is to explore one of these different pathways in the pathogen L. interrogans as well as in the model saprophyte strain L. biflexa by several approaches including molecular microbiology, biochemistry and structural biology.
Further progress in our understanding of the virulence of Leptospira will contribute to the
development of novel strategies for the diagnostic and prevention of this neglected emerging
Picardeau M, Bulach DM, Bouchier C, Zuerner RL, Zidane N, Wilson PJ, Creno S, Kuczek ES, Bommezzadri S, Davis JC, McGrath A, Johnson MJ, Boursaux-Eude C, Seemann T, Rouy Z, Coppel RL, Rood JI, Lajus A, Davies JK, Médigue C, Adler B. Genome sequence of the saprophyte Leptospira biflexa provides insights into the evolution of Leptospira and the pathogenesis of leptospirosis. PLoS One. 2008 Feb 13;3(2):e1607.
Lambert A, Picardeau M, Haake DA, Sermswan RW, Srikram A, Adler B, Murray GA. FlaA proteins in Leptospira interrogans are essential for motility and virulence but are not required for formation of the flagellum sheath. Infect Immun. 2012 Jun;80(6):2019-25.
Slamti L, de Pedro MA, Guichet E, Picardeau M. Deciphering morphological determinants of the helix-shaped Leptospira. J Bacteriol. 2011 Nov;193(22):6266-75.
Ko AI, Goarant C, Picardeau M. Leptospira: the dawn of the molecular genetics era for an emerging zoonotic pathogen. Nat Rev Microbiol. 2009 Oct;7(10):736-47.
Lourdault K, Cerqueira GM, Wunder EA Jr, Picardeau M. Inactivation of clpB in the pathogen Leptospira interrogans reduces virulence and resistance to stress conditions. Infect Immun. 2011 Sep;79(9):3711-7.
Slamti L, Picardeau M. Construction of a library of random mutants in the spirochete Leptospira biflexa using a mariner transposon.
Methods Mol Biol. 2012;859:169-76.
Figueira CP, Croda J, Choy HA, Haake DA, Reis MG, Ko AI, Picardeau M. Heterologous expression of pathogen-specific genes ligA and ligB in the saprophyte Leptospira biflexa confers enhanced adhesion to cultured cells and fibronectin. BMC Microbiol. 2011 Jun 9;11:129.