Two intestinal bacterial strains MT4s-5 and MT42 involved in the degradation of (-)-epigallocatechin (EGC) were isolated from rat feces. Strain MT4s-5 was tentatively identified as Adlercreutzia equolifaciens. This strain converted EGC into not only 1-(3, 4, 5-trihydroxyphenyl)-3-(2, 4, 6-trihydroxyphenyl)propan-2-ol (1), but also 1-(3, 5-dihydroxyphenyl)-3-(2, 4, 6-trihydroxyphenyl)propan-2-ol (2), and 4'-dehydroxylated EGC (7). Type strain (JCM 9979) of Eggerthella lenta was also found to convert EGC into 1. Strain MT42 was identified as Flavonifractor plautii and converted 1 into 4-hydroxy-5-(3, 4, 5-trihydroxyphenyl)valeric acid (3) and 5-(3, 4, 5-trihydroxyphenyl)-γ-valerolactone (4) simultaneously. Strain MT42 also converted 2 into 4-hydroxy-5-(3, 5-dihydroxyphenyl)valeric acid (5), and 5-(3, 5-dihydroxyphenyl)-γ-valerolactone (6). Furthermore, F. plautii strains ATCC 29863 and ATCC 49531 were found to catalyze the same reactions as strain MT42. Interestingly, formation of 2 from EGC by strain MT4s-5 occurred rapidly in the presence of hydrogen supplied by syntrophic bacteria. Strain JCM 9979 also formed 2 in the presence of the hydrogen or formate. Strain MT4s-5 converted 1, 3, and 4 to 2, 5, and 6, respectively, and the conversion was stimulated by hydrogen, whereas strain JCM 9979 could catalyze the conversion only in the presence of hydrogen or formate. On the basis of the above results together with previous reports, the principal metabolic pathway of EGC and EGCg by catechin-degrading bacteria in gut tract is proposed.
