Reclassification of Bifidobacterium stercoris Kim et al. 2010 as a later heterotypic synonym of Bifidobacterium adolescentis

Abstract

The taxonomic position of Bifidobacterium stercoris Eg1T ( = JCM 15918T) 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 18363T. 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 5756T and B. adolescentis ATCC 15703T. MLSA revealed close relatedness between B. stercoris KCTC 5756T and B. adolescentis CCUG 18363T, 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).