Environmental Sciences and Life Sciences Divisions, Oak Ridge National Laboratory, Oak Ridge, TN 37831; Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824; Center for Biotechnology Information, National Institutes of Health, Bethesda, MD 20894; and Uniformed Services University of the Health Sciences, Bethesda, MD 20814 (At 2003-03-21)