1. Departments of Molecular Physiology and Biological Physics, and
2. Microbiology, University of Virginia, Charlottesville, VA 22906‐0011, USA,
3. Research Center of Aging and Adaptation, Shinshu University School of Medicine, Matsumoto 390‐8621, Japan and
4. Osaka Medical Center, PRESTO, JST, Osaka 537‐8511, Japan