Novel microbiota Mesosutterella faecium sp. nov. has a protective effect against inflammatory bowel disease

A novel Gram-negative, obligate anaerobe, non-motile, flagella-lacking, catalase- and oxidase-negative, coccobacilli-shaped bacterial strain designated AGMB02718^T was isolated from swine feces. The 16S rRNA gene analysis indicated that strain AGMB02718^T belonged to the genus Mesosutterella with the highest similarity to M. multiformis 4NBBH2^T (= DSM 106860^T) (sequence similarity of 96.2%), forming a distinct phylogenetic lineage. Its growth occurred at 25-45°C (optimal 37°C) and in 0.5-1% NaCl (optimal 0.5%). Strain AGMB02718^T was asaccharolytic and contained menaquinone 6 (MK-6) and methylmenaquinone 6 (MMK-6) as the predominant respiratory quinones. The major cellular fatty acids in the isolate were C_18:1ω9c and C_16:0. Based on the whole-genome sequencing analysis, strain AGMB02718^T had a 2,606,253 bp circular chromosome with a G + C content of 62.2%. The average nucleotide identity value between strain AGMB02718^T and M. multiformis 4NBBH2^T was 72.1%, while the digital DNA-DNA hybridization value was 20.9%. Interestingly, genome analysis suggested that strain AGMB02718^T possessed a low-toxicity lipopolysaccharide (LPS) because the genome of the isolate does not include lpxJ and lpxM genes for Kdo₂-Lipid A (KLA) assembly, which confers high toxicity to LPS. Moreover, in vitro macrophage stimulation assay confirmed that AGMB02718^T produced LPS with low toxicity. Because the low-toxicity LPS produced by the Sutterellaceae family is involved in regulating host immunity and low-toxicity LPS-producing strains can help maintain host immune homeostasis, we evaluated the anti-inflammatory activity of strain AGMB02718^T against inflammatory bowel disease (IBD). As a result, strain AGMB02718^T was able to prevent the inflammatory response in a dextran sulfate sodium (DSS)-induced colitis model. Therefore, this strain represents a novel species of Mesosutterella that has a protective effect against DSS-induced colitis, and the proposed name is Mesosutterella faecium sp. nov. The type strain is AGMB02718^T (=GDMCC 1.2717^T = KCTC 25541^T).