Clostridium saccharogumia sp. nov. and Lactonifactor longoviformis gen. nov., sp. nov., two novel human faecal bacteria involved in the conversion of the dietary phytoestrogen secoisolariciresinol diglucoside

Two anaerobic bacteria involved in the conversion of the plant lignan secoisolariciresinol diglucoside were isolated from faeces of a healthy male adult. The first isolate, strain SDG-Mt85-3Db, was a mesophilic strictly anaerobic Gram-positive helically coiled rod. Based on 16S r RNA gene sequence analysis, its nearest relatives were Clostridium cocleatum (96.7% similarity) and Clostridium ramosum (96.6%). In contrast to these species, the isolate was devoid of alpha-galactosidase and -glucosidase and did not grow on maltose, melibiose, raffinose, rhamnose and trehalose. The hypothesis that strain SDG-Mt85-3Db represents a new bacterial species of the Clostridium cluster XVIII was confirmed by DNA–DNA hybridisation experiments. The G+C content of DNA of strain SDG-Mt85-3Db (30.7±0.8 mol%) was comparable with that of Clostridium butyricum, the type species of the genus Clostridium. The name Clostridium saccharogumia is proposed for strain SDG-Mt85-3Db (=DSM 17460T=CCUG 51486T). The second isolate, strain ED-Mt61/PYG-s6, was a mesophilic strictly anaerobic Gram-positive regular rod. Based on 16S rRNA gene sequence analysis, its nearest relatives were Clostridium amygdalinum (93.3%), Clostridium saccharolyticum (93.1%) and Ruminococcus productus (93.0%). The isolate differed from these species in its ability to dehydrogenate enterodiol. It also possessed alpha-arabinosidase and -galactosidase and had a higher G+C content of DNA (48.0 mol%). According to these findings, it is proposed to create a novel genus, Lactonifactor, and a novel species, Lactonifactor longoviformis, to accommodate strain ED-Mt61/PYG-s6. The type strain is DSM 17459T (=CCUG 51487T).