1. L. Bry and J. I. Gordon, Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110, USA.
2. P. G. Falk, Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110, USA, and Department of Medicine and Laboratory of Medical Microbial Ecology, Karolinska Institute, S-17177 Stockholm, Sweden.
3. T. Midtvedt, Laboratory of Medical Microbial Ecology, Karolinska Institute, S-17177 Stockholm, Sweden.