Bifidobacterium fermentum sp. nov. and Bifidobacterium aquikefiricola sp. nov., isolated from water kefir.

Four strains, representing two novel Bifidobacterium species, were isolated from water kefir, a fermented beverage. 16S rRNA gene analysis suggested that the novel species share high identities (98.82-98.89%) with Bifidobacterium aquikefiri LMG 28769^T. Complete genomes were assembled with a short- and long-read hybrid sequencing approach. In agreement with the 16S rRNA gene analysis, phylogenetics with 117 marker genes places the novel species closest to B. aquikefiri LMG 28769^T as well. The isolates have average nucleotide identity (ANI) scores ranging from 81.46 to 84.84% and digital DNA-DNA hybridization (dDDH) scores from 23.9 to 38.5% with the closest related species, as well as ANI scores between the proposed new species of 80.50%, indicating that the isolates represent two novel species. Matrix-assisted laser desorption/ionization-time of flight chemotaxonomic analysis supported the gene-based taxonomic placement. We propose the names Bifidobacterium fermentum sp. nov. and Bifidobacterium aquikefiricola sp. nov. for these novel species within the Bifidobacterium genus. The proposed type strain B. fermentum WK012_4_13^T (= LMG 33104^T = DSM 116073^T; GenBank accession number GCF_041080835.1) has a genome size of 2.43 Mbp, with a G+C content of 56.00 mol%. The proposed type strain for B. aquikefiricola WK041_4_12^T (= LMG 33105^T = DSM 116074^T; GenBank accession number GCF_041080795.1) has a genome size of 2.36 Mbp and a G+C content of 53.94 mol%. B. fermentum cells are Gram-positive staining, non-motile, non-spore-forming, fructose-6-phosphate phosphoketolase (F6PPK)-positive, catalase- and oxidase-negative and bacillary club shaped. B. aquikefiricola cells are Gram-positive staining, non-motile, non-spore-forming, F6PPK-positive, catalase- and oxidase-negative and square rod shaped.