1. Department of Bacteriology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan1
2. Department of Biochemistry, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan2
3. Department of Food Science, Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri099-2422, Japan3