Bifidobacterium intestinale sp. nov., and Blautia caeci sp. nov., from the Human Gut Microbiome with Candidate...

Two novel Gram-stain-positive, anaerobic, and non-motile bacterial strains, designated M3-R-103^T and C3-R-101^T, were isolated from human faecal samples and subjected to comprehensive taxonomic characterization together with evaluation of selected functional properties. Phylogenetic analysis based on 16S rRNA gene sequences demonstrated that strain M3-R-103^T is affiliated with the genus Bifidobacterium, whereas strain C3-R-101^T belongs to the genus Blautia. Strain M3-R-103^T exhibited the highest 16S rRNA gene sequence similarity (98.9%) to Bifidobacterium pseudocatenulatum DSM 20438^T, while strain C3-R-101^T showed 98.6% similarity to Blautia hominis KB1^T. The draft genome sizes of strains M3-R-103^T and C3-R-101^T were 2.08 Mbp and 6.40 Mbp, respectively, with DNA G+C contents of 56.3 mol% and 46.7 mol%. Both strains demonstrated tolerance to simulated gastrointestinal stress conditions, including exposure to acidic pH (2.0) and bile salts (0.3%). In vitro assays revealed measurable antioxidant, α-amylase inhibitory, and anti-inflammatory activities. Specifically, DPPH radical scavenging activity ranged from 38.28 ± 8.35% to 58.83 ± 9.35%, α-amylase inhibition ranged from 47.12 ± 2.76% to 69.19 ± 3.83%, and inhibition of albumin denaturation ranged from 52.99 ± 2.70% to 58.16 ± 8.00%. Based on combined phylogenetic, genomic, and phenotypic evidence, strains M3-R-103^T and C3-R-101^T represent two novel species within their respective genera. We therefore propose the names Bifidobacterium intestinale sp. nov. (type strain M3-R-103^T = KCTC 25443^T = CGMCC 1.19415^T) and Blautia caeci sp. nov. (type strain C3-R-101^T = KCTC 25440^T = CGMCC 1.17981^T).