Abstract
Two Gram-stain-negative, straight rods, non-motile, asporogenous, catalase-negative and obligately anaerobic butyrate-producing strains, HLW78(T) and CYL33, were isolated from faecal samples of two healthy Taiwanese adults. Phylogenetic analyses of 16S rRNA and DNA mismatch repair protein MutL (mutL) gene sequences revealed that these two novel strains belonged to the genus Faecalibacterium. On the basis of 16S rRNA and mutL gene sequence similarities, the type strains Faecalibacterium butyricigenerans AF52-21(T)(98.3-98.1 % and 79.0-79.5 % similarity), Faecalibacterium duncaniae A2-165(T)(97.8-97.9 % and 70.9-80.1 %), Faecalibacterium hattorii APC922/41-1(T)(97.1-97.3 % and 80.3-80.5 %), Faecalibacterium longum CM04-06(T)(97.8-98.0% and 78.3 %) and Faecalibacterium prausnitzii ATCC 27768(T)(97.3-97.4 % and 82.7-82.9 %) were the closest neighbours to the novel strains HLW78(T) and CYL33. Strains HLW78(T) and CYL33 had 99.4 % both the 16S rRNA and mutL gene sequence similarities, 97.9 % average nucleotide identity (ANI), 96.3 % average amino acid identity (AAI), and 80.5 % digital DNA-DNA hybridization (dDDH) values, indicating that these two strains are members of the same species. Phylogenomic tree analysis indicated that strains HLW78(T) and CYL33 formed an independent robust cluster together with F. prausnitzii ATCC 27768(T). The ANI, AAI and dDDH values between strain HLW78(T) and its closest neighbours were below the species delineation thresholds of 77.6-85.1 %, 71.4-85.2 % and 28.3-30.9 %, respectively. The two novel strains could be differentiated from the type strains of their closest Faecalibacterium species based on their cellular fatty acid compositions, which contained C(18 : 1) ω7c and lacked C(15 : 0) and C(17 : 1) ω6c, respectively. Phenotypic, chemotaxonomic and genotypic test results demonstrated that the two novel strains HLW78(T) and CYL33 represented a single, novel species within the genus Faecalibacterium, for which the name Faecalibacterium taiwanense sp. nov. is proposed. The type strain is HLW78(T) (=BCRC 81397(T)=NBRC 116372(T)).