A Gram-negative, obligate anaerobic genus within the Bacteroidetes phylum (family Rikenellaceae). Alistipes occupies a complex and context-dependent role in the gut ecosystem, with some species showing anti-inflammatory properties while the genus as a whole is enriched in colorectal cancer. Key species include A. finegoldii, A. putredinis, and A. indistinctus, each with distinct disease associations.
Role in Gut Ecosystem
- Bile-resistant anaerobe that contributes to bile acid deconjugation and secondary bile acid production, sharing this metabolic niche with parabacteroides and bacteroides fragilis.
- Produces indole from tryptophan metabolism, generating aryl hydrocarbon receptor (AhR) ligands including indole-3-acetic acid and indole-3-propionic acid that support mucosal immunity and gut barrier integrity.
- Ferments complex carbohydrates to produce short chain fatty acids, primarily acetate and propionate.
- One of the 18 dominant bacterial genera identified in the human colon [sobhani 2011 microbial dysbiosis colorectal cancer].
Disease Associations
Colorectal Cancer -- Enrichment
- Enriched in CRC and contributes to cancer progression. A. indistinctus is positively correlated with mast cell infiltration, IL-6, and IL6R immune activators in advanced-stage (III-IV) CRC [liu 2023 colorectal cancer progression microbiome signature].
- Part of the progression-associated microbiome signature distinguishing early from advanced CRC, alongside Proteus and parabacteroides.
- Enrichment in CRC may relate to altered bile acid profiles in the tumor microenvironment, where secondary bile acids (deoxycholic acid) promote epithelial proliferation and DNA damage.
Autoimmune Disease -- Depletion
- Significantly depleted in Graves' disease alongside bacteroides fragilis and parabacteroides, contributing to the loss of anti-inflammatory commensals that characterizes thyroid autoimmunity [su 2020 gut microbiota immune imbalance graves].
- Higher baseline abundance in multiple sclerosis patients (Bacteroidetes expansion), but this varies by study and disease phase [troci 2022 b cell depletion reverses dysbiosis ms].
Cardiovascular Disease
- Ischemic stroke causally affects Alistipes abundance in reverse MR analysis, indicating that cerebrovascular events alter this genus [dai 2024 gut microbiota cvd bidirectional mr].
Autism Spectrum Disorder
- Altered abundance reported in ASD, though direction of change varies across studies [strati 2017 altered gut microbiota mycobiota asd].
Key Metabolites
- Indole derivatives (indole-3-acetic acid, indole-3-propionic acid) -- AhR ligands; mucosal immune regulators
- Secondary bile acids -- deoxycholic acid, lithocholic acid; immunomodulatory via FXR/TGR5
- Acetate and propionate -- short chain fatty acids supporting gut barrier and immune homeostasis
Species-Level Complexity
The genus illustrates why species-level resolution matters in microbiome research:
- A. finegoldii -- associated with anti-inflammatory effects; produces indole derivatives
- A. putredinis -- core commensal; abundant in healthy gut
- A. indistinctus -- positively correlated with pro-inflammatory immune infiltrates in CRC
- This species-level divergence explains apparently contradictory genus-level findings across disease contexts.
Connections
- colorectal cancer -- enriched in CRC; A. indistinctus linked to immune activation in advanced tumors
- Graves' disease -- depleted alongside other Bacteroidetes commensals
- parabacteroides -- co-depleted in autoimmune disease; shared bile acid metabolic niche
- bacteroides fragilis -- co-depleted in Graves' disease; fellow Bacteroidetes commensal
- tryptophan -- indole production from tryptophan supports AhR signaling and mucosal immunity
- cardiovascular disease -- abundance altered by ischemic stroke
- short chain fatty acids -- acetate and propionate producer
- dysbiosis -- context-dependent marker; depletion in autoimmunity, enrichment in cancer
- inflammation -- species-dependent: anti-inflammatory (A. finegoldii) vs pro-inflammatory (A. indistinctus in CRC)