1. Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA.
2. Laboratoire Adaptation et Pathogénie des Microorganismes, Université Joseph Fourier, Institut Jean Roget, F-38041 Grenoble, France.
3. CNRS UMR5163, F-38041 Grenoble, France.
4. Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.