Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.