Isolation and characterization of a novel Waltera species and reclassification of Brotolimicola acetigignens Hitch et al. 2022 as Waltera acetigignens comb. nov.

Abstract

Obligately anaerobic, Gram-stain-negative, wavy rods, strains 17YCFAHCo10, 18YCFAH0.3Co2 and 19YCFAH0.3Co2, were isolated from faecal samples of healthy Japanese people. The three isolates showed the highest 16S rRNA gene sequence similarity to Waltera intestinalis WCA3-601-WT-6HT (99.2-100 %) and Brotolimicola acetigignens f_CXYT (99.2-99.7 %). The 16S rRNA gene sequence analysis showed that the three isolates formed a cluster with W. intestinalis WCA3-601-WT-6HT. Strain 19YCFAH0.3Co2 formed a subcluster with the type strain of W. intestinalis and did not form a cluster with the other two isolates. B. acetigignens f_CXYT also formed a cluster with W. intestinalis WCA3-601-WT-6HT and three isolates. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain 19YCFAH0.3Co2 and W. intestinalis WCA3-601-WT-6HT were higher (72 % dDDH and 97 % ANI) than the cut-off values for species delimitation, indicating that strain 19YCFAH0.3Co2 is W. intestinalis. On the other hand, the dDDH and ANI values between strains 17YCFAHCo10 and 18YCFAH0.3Co2 and the type strain of W. intestinalis were lower (<34 % dDDH and <87 % ANI) than the cut-off values for species delimitation, indicating that these two isolates are different species from W. intestinalis. The percentage of conserved proteins and the average amino acid identity values support the assignment of the isolates to the genus Waltera. Strains 17YCFAHCo10 and 18YCFAH0.3Co2 could be distinguished from W. intestinalis by their inability to ferment melibiose and ribose and lack of activity for β-glucuronidase. In addition, the dDDH and ANI values between two strains (17YCFAHCo10 and 18YCFAH0.3Co2) and B. acetigignens f_CXYT were higher (>78 % dDDH and >97 % ANI), indicating these two strains and B. acetigignens are the same species. As the genus Waltera has priority, B. acetigignens is transferred to the genus Waltera as Waltera acetigignens comb. nov. The type strain of W. acetigignens is f_CXYT (=JCM 34988T=DSM 107528T).