Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu|Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu|Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu|Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu|Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu|Department of Microbiology, University of Washington, Seattle, WA 98195, USA. mbrittna@uw.edu