Genome-based, phenotypic and chemotaxonomic classification of Faecalibacterium strains: proposal of three novel species Faecalibacterium duncaniae sp. nov., Faecalibacterium hattorii sp. nov. and Faecalibacterium gallinarum sp. nov.

Faecalibacterium prausnitzii is one of the most important butyrate-producing bacteria in the human gut. Previous studies have suggested the presence of several phylogenetic groups, with differences at the species level, in the species, and a taxonomic re-evaluation is thus essential for further understanding of ecology of the important human symbiont. Here we examine the phenotypic, physiological, chemotaxonomic and phylogenomic characteristics of six F prausnitzii strains (BCRC 81047(T) =ATCC 27768(T), A2-165(T)=JCM 31915(T), APC918/95b=JCM 39207, APC942/30-2=JCM 39208. APC924/119=JCM 39209 and APC922/41-1(T) =JCM 39210(T)) deposited in public culture collections with two reference strains of Faecalibacterium butyricigenerans JCM 39212(T) and Faecalibacterium longum JCM 39211(T). Faecalibacterium sp. JCM 17207(T) isolated from caecum of broiler chicken was also included. Three strains of F. prausnitzii (BCRC 81047(T), JCM 39207 and JCM 39209) shared more than 96.6% average nucleotide identity (ANI) and 69.6% digital DNA-DNA hybridization (dDDH) values, indicating that the three strains are members of the same species. On the other hand, the remaining three strains of F prausnitzii (JCM 31915(T), JCM 39208 and JCM 39210(T)) were clearly separated from the above three strains based on the ANI and dDDH values. Rather, JCM 39208 showed ANI and dDDH values over the cut-off values of species discrimination (>70% dDDH and >95-96% ANI) with F longum JCM 39211(T). whereas JCM 31915(T), JCM 39210(T) and JCM 17207(T) did not share dDDH and ANI values over the currently accepted cut-off values with any of the tested strains, including among them. Furthermore, the cellular fatty acid patterns of these strains were slightly different from other F prausnitzii strains. Based on the collected data, F prausnitzii JCM 31915(T), F. prausnitzii JCM 39210(T) and Faecalibacterium sp. JCM 17207(T) represent three novel species of the genus Faecalibacterium, for which the names Faecalibacterium duncaniae sp. nov. (type strain JCM 31915(T)=DSM 17677(T) =A2-165(T)), Faecalibacterium hattorii sp. nov. (type strain JCM 39210(T)=DSM 107841(T) =APC922/41-1(T)) and Faecalibacterium gallinarum sp. nov. (type strain JCM 17207(T)=DSM 23680 1 =ic1379(T)) are proposed.

Automated summary

In this study, the phenotypic, physiological, chemotaxonomic, and phylogenomic characteristics of six Faecalibacterium prausnitzii strains were examined. The results showed that three of the strains belong to the same species, while the other three are clearly separated. The cellular fatty acid patterns of these strains were also slightly different. Based on these findings, three new species of the genus Faecalibacterium are proposed.