1. Division of Science and Mathematics, Eastern Oklahoma State College, Idabel, Oklahoma 74745, U.S.A. (e-mail: )
2. Department of Microbiology, Midwestern University, Glendale, Arizona 85308, U.S.A. (e-mail: )
3. San Diego Field Station, Western Ecological Research Center, U.S. Geological Survey, 4165 Spruance Road, Suite 200, San Diego, California 92101, U.S.A. (e-mail: )