1. University of Calgary, Department of Microbiology and Infectious Diseases, Faculty of Medicine, 3330 Hospital Dr., NW Calgary, Alberta T2N 4N1, Canada.
2. University Zürich, Department of Microbiology, Institute of Plant Biology, CH-8057 Zürich, Switzerland.
3. University Zürich, Department of Microbiology, Institute of Plant Biology, CH-8008 Zürich, Switzerland.