1. Department of Environmental Science and Engineering and International Environmental Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea, Department of Soil, Water, and Climate and BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108, and School of Biological Sciences, Seoul National University, NS70, 56-1 Daehak-dong, Kwanak-gu, Seoul 151-742, Republic of Korea