1. Department of Bacteriology; Yokohama City University School of Medicine; Yokohama, Kanagawa 236-0004 Japan
2. Laboratory of Microbiology, Department of Biotechnology; Akita Prefectural University; Akita, Akita 010-0195 Japan
3. Department of Environmental Life Science; Graduate School of Life Science, Tohoku University; Sendai Miyagi 980-8577 Japan