Coxiella burnetii is an obligate intracellular gram-negative bacterium responsible of the zoonosis Q fever, a disease that manifests as an acute flu-like illness. Due to its high infectivity it has been classified as a class B biothreat. In natural infections Coxiella mainly targets macrophages whereas in vitro is capable of infecting a wide variety of cell types. As several other pathogens Coxiella replicates in a large phagosomal vacuole, but differently from any other known pathogen, Coxiella has the capacity of thriving in a parasitophorous vacuole which is biochemically indistinguishable from lysosomes. Despite the interest that Coxiella infections raise, its obligate intracellular nature has hampered the research activity due to the impossibility of genetic manipulation and growth in broth. The mechanisms of subversion of host functions remain therefore obscure and the number of Coxiella virulence factors identified is limited to the bacterial LPS. The recent characterization of a specific growth medium that allows axenic growth of Coxiella opens the way to genetic engineering of the bacterium. The aim of this project is the large-scale identification of Coxiella virulence factors by generating a bank of mutants by transposon mutagenesis. This will be coupled to the set up of robust high throughput screens to identify phenotypes that will allow the characterization of virulence factors.