Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.|Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.