Strain Eg1(T), an anaerobic, Gram-stain-positive, non-motile and non-spore-forming bacterium, was isolated from human faeces. The optimal temperature for growth was 37 �XC and tests for oxidase and catalase activities gave negative results. Fructose-6-phosphate phosphoketolase activity was detected. Acid was produced during fermentation of several substrates, including glucose. The end products of glucose fermentation were acetic acid and lactic acid, which were produced in a molar ratio of 1.76 : 1 (approximately 3 : 2). The G+C content was 57.8 mol%. Comparative analysis of 16S rRNA gene sequences showed that strain Eg1(T) was closely related to Bifidobacterium adolescentis YIT 4011(T) (98.36 % 16S rRNA gene sequence similarity) and Bifidobacterium ruminantium JCM 8222(T) (97.93 %) and analysis of hsp60 sequences showed that strain Eg1(T) was closely related to B. adolescentis JCM 1275(T) (99.35 % hsp60 sequence similarity) and B. ruminantium JCM 8222(T) (92.13 %). However, despite these degrees of similarity being high enough for strain Eg1(T) to be included at the same species level as B. adolescentis and B. ruminantium (96.5-100 % for the genus Bifidobacterium), the isolate could be distinguished from B. adolescentis KCTC 3216(T) and B. ruminantium KCTC 3425(T) by low levels of DNA-DNA relatedness (41 and 17 %, respectively). Based on phenotypic, genotypic and phylogenetic analyses, we propose that strain Eg1(T) is classified in a novel species, Bifidobacterium stercoris sp. nov. The type strain is Eg1(T) (=KCTC 5756(T) =JCM 15918(T)).

The taxonomic position of Bifidobacterium stercoris Eg1(T) (= JCM 15918(T)) based on comparative 16S rRNA gene and hsp60 sequence analyses was found to be controversial, as the strain showed high similarity to the type strain of Bifidobacterium adolescentis, CCUG 18363(T). Therefore, the relationship between the two species was investigated by a taxonomic study that included, in addition to re-evaluation of the 16S rRNA gene sequence, determination of DNA-DNA binding and multilocus sequence analysis (MLSA) of housekeeping genes encoding the DNA-directed RNA polymerase B subunit (rpoC), putative xylulose-5-phosphate/fructose-6-phosphate phosphoketolase (xfp), elongation factor EF-G (fusA), 50S ribosomal protein L2 (rplB) and DNA gyrase B subunit (gyrB). Comparative 16S rRNA gene sequence analysis showed relatively high similarity (98.9 %) between B. stercoris KCTC 5756(T) and B. adolescentis ATCC 15703(T). MLSA revealed close relatedness between B. stercoris KCTC 5756(T) and B. adolescentis CCUG 18363(T), with 99.3-100 % similarity between the rpoC, xfp, fusA, rplB and gyrB gene sequences. In addition, relatively high dnaJ1 gene sequence similarity of 97.7 % was found between the strains. Similar phenotypes and a high DNA-DNA binding value (78.9 %) confirmed that B. stercoris and B. adolescentis are synonymous. Based on these results, it is proposed that the species Bifidobacterium stercoris Kim et al. 2010 should be reclassified as a later heterotypic synonym of Bifidobacterium adolescentis Reuter 1963 (Approved Lists 1980).