Prof. Bernard C. Rossier

Ms Marie-Madeleine
+41 22 704 36 41


Chemin Rieu 17
P.O. Box 270
1211 Geneva 17
+41 22 704 36 36
+41 22 704 36 37


Raphael H. Valdivia

Duke University Medical Center, Durham (USA)

Department of Molecular Genetics and Microbiology

Tuesday, October 23, 16:30 - 17:00

NextGen approaches to tackle "genetically intractable" microbial systems

Chlamydia trachomatis, a pathogen responsible for diseases of significant clinical and public health importance, remains poorly characterized because of its intractability to routine molecular genetic manipulation.  In this lecture, I will describe the development of both proteomic, functional, genomic, and finally, deep DNA sequencing approaches to define gene function in these pathogens. In particular, I will describe a combinatorial approach to rapidly generate a comprehensive library of genetically defined mutants.

We used chemical mutagenesis, coupled with whole genome sequencing (WGS) and a system for DNA exchange within infected cells, to generate Chlamydia mutants with distinct phenotypes, map the underlying genetic lesions, and generate isogenic strains. As a result, we identified mutants with altered glycogen metabolism, including attenuated strains defective for effector protein secretion. The methods described here, coupled with chemically induced gene variation and WGS to establish genotype-phenotype associations should be broadly applicable to the large list of medically and environmentally important microorganisms currently intractable to genetic analysis.



Raphael H. Valdivia obtained his PhD in 1997 with Stanley Falkow at Stanford University. He was then awarded a Damon Runyon Fellowship to study the molecular basis of membrane transport with Randy Schekman at the University of California, Berkeley. He started his independent position at Duke University in 2002, with a new programme to study the cellular microbiology of Chlamydia trachomatis, the agent of trachoma and many sexually transmitted infections. In the process he has pioneered methods for the analysis of microbes considered recalcitrant to conventional genetic and biochemical approaches. Raphael H. Valdivia is a Burroughs Wellcome Investigator in the Pathogenesis of infectious Diseases.