Parabacteroides

Role in Gut Ecosystem#

Member of the core Bacteroidetes community that dominates the human colon, contributing to polysaccharide degradation and bile acid biotransformation.

P. distasonis deconjugates primary bile acids and produces secondary bile acids including lithocholic acid, influencing Farnesoid X Receptor (FXR) and TGR5 signaling pathways that regulate immune tone and metabolic homeostasis.

Produces Short-Chain Fatty Acids (SCFAs) (primarily succinate and acetate) that feed cross-feeding networks supporting Butyrate producers like Faecalibacterium prausnitzii. Contributes to colonization resistance against pathogens through niche competition and bile acid-mediated inhibition.

Metabolic Protection#

Depleted in obesity and Type 2 Diabetes, where its loss correlates with impaired bile acid signaling and metabolic Metal-Driven Inflammation. P. distasonis supplementation in mouse models improves glucose tolerance, reduces adiposity, and ameliorates hepatic steatosis via bile acid-FXR-FGF15 axis modulation.

Autoimmune Disease#

Significantly depleted in Graves' Disease alongside Bacteroides fragilis and Alistipes, contributing to the pro-inflammatory gut environment that drives thyroid autoimmunity.^{[1]Alteration in gut microbiota is associated with immune imbalance in Graves' diseaseSu X, Yin X, Liu Y et al. · 2020Open reference 1 ↓}

Decreased in Multiple Sclerosis at baseline; B-cell depletion therapy (ocrelizumab) further reduces Parabacteroides as the overall microbiome shifts toward Firmicutes restoration.^{[2]B-cell-depletion reverses dysbiosis of the microbiome in multiple sclerosis patientsAlba Troci, Olga Zimmermann, Daniela Esser et al. · 2022Open reference 2 ↓}

Cancer—Opposite Directionality#

Shows true opposite directionality in the Islam 2022 meta-analysis: increased in cancer cohorts but decreased in autoimmune disease cohorts.^{[3]Reproducible and opposing gut microbiome signatures distinguish autoimmune diseases and cancers: a systematic review and meta-analysisMd Zohorul Islam, Melissa Tran, Tao Xu et al. · 2022Open reference 3 ↓}

Enriched in Colorectal Cancer progression—identified among genera contributing to CRC stage advancement alongside Proteus and Alistipes.^{[4]Identification of colorectal cancer progression-associated intestinal microbiome and predictive signature constructionJungang Liu, Xiaoliang Huang, Chuanbin Chen et al. · 2023Open reference 4 ↓}

This paradox may reflect context-dependent bile acid metabolism: protective secondary bile acids in healthy mucosa versus tumor-promoting deoxycholic acid in the dysbiotic cancer microenvironment.

Key Metabolites#

Secondary bile acids (lithocholic acid, ursodeoxycholic acid)—immunomodulatory via FXR/TGR5. Succinate—intermediate metabolite; fuel for cross-feeding networks. Acetate—contributes to gut barrier maintenance and systemic anti-inflammatory signaling.