Segatella intestinalis sp. nov., and Parabacteroides caeci sp. nov., novel potential probiotics from the human gut microbiome

초록

Two bacterial strains, B2-R-102T and W1-Q-101T, were isolated from the feces of a healthy Korean individual. These strains were Gram-stain negative, anaerobic, and non-motile, growing optimally between 20 and 40 degrees C and at pH 5.5-8.0. Importantly, they survived at pH 2.0 and tolerated 0.3% bile salts and pepsin after a 4 h exposure. The strains demonstrated in vitro antioxidant activity, inhibiting DPPH radicals by 48.12 +/- 1.45 and 70.80 +/- 12.8%, respectively. Furthermore, they inhibited alpha-amylase activity by 46.52 +/- 4.42 to 60.84 +/- 2.20%, compared to 74.82 +/- 0.76% inhibition by sitagliptin. In vitro, anti-inflammatory assays revealed 57.77 +/- 3.15 to 62.39 +/- 2.23% inhibition of albumin protein denaturation, comparable to aspirin 72 +/- 2.39% inhibition. The abundant cellular fatty acids were C15:0, C16:0, iso-C15:0, C18:1 omega 9c, anteiso-C15:0 and iso-C17:0 3-OH. Neither strain exhibited haemolytic activity, and genomic analysis revealed no acquired antibiotic resistance or virulence genes. Phylogenetic analysis showed that B2-R-102T and W1-Q-101T belonged to the genera Segatella and Parabacteroides, with 96.9 and 97.7% 16S rRNA gene sequence similarities to Segatella copri CB7T and Parabacteroides goldsteinii DSM 19448T, respectively. Furthermore, biosynthetic gene cluster analysis revealed the potential for antimicrobial thiopeptides, lanthipeptides, and non-ribosomal peptides (NRPs). In silico average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were below the thresholds to distinguish novel species. Based on phenotypic, genomic, and phylogenetic analysis, we propose the names Segatella intestinalis sp. nov. (type strain B2-R-102T = CGMCC 1.17963T = KCTC 25417T) and Parabacteroides caeci sp. nov. (type strain W1-Q-101T = KCTC 25456T = CGMCC 1.17991T).

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