Eubacterium Rectale

Eubacterium rectale (recently reclassified as Agathobacter rectalis) is a Gram-positive, strictly anaerobic, non-spore-forming bacterium that belongs to Clostridium cluster XIVa within the lachnospiraceae family. It is one of the most abundant butyrate producers in the healthy human colon, typically comprising 1-5% of total fecal bacteria. Together with faecalibacterium prausnitzii (Clostridium cluster IV), it accounts for the majority of colonic butyrate production.

The consistent depletion of E. rectale across cardiovascular, autoimmune, neurological, and metabolic diseases makes it — alongside F. prausnitzii — one of the most reliable bacterial indicators of gut health. Its iron-sulfur cluster-dependent butyrate pathway provides a metallomics explanation for why this organism is so vulnerable to the environmental perturbations that precede disease.

Metal Dependencies

E. rectale's butyrate synthesis pathway depends critically on iron:

  • The butyryl-CoA dehydrogenase complex uses [4Fe-4S] and [2Fe-2S] iron-sulfur clusters for electron transfer in the conversion of crotonyl-CoA to butyryl-CoA.
  • These clusters are targets for displacement by toxic metals (Cd, Pb, Hg), which can intercalate into the iron-sulfur scaffold and inactivate the enzyme.
  • This molecular vulnerability links environmental metal exposure to butyrate depletion: heavy metal stress preferentially disables the very enzymes that produce the gut's primary anti-inflammatory metabolite.

The pattern is striking: the taxa most vulnerable to metal exposure (E. rectale, roseburia, faecalibacterium prausnitzii) are precisely the taxa most consistently depleted in disease. This is not coincidence — it is the predictable consequence of iron-sulfur cluster chemistry.

Key Enzymes and Virulence Factors

E. rectale has no virulence factors. Its enzymatic profile is dedicated to fiber fermentation and butyrate production:

  • Acetyl-CoA acetyltransferase: Condenses two acetyl-CoA molecules to initiate the butyrate pathway.
  • Butyryl-CoA dehydrogenase: The iron-sulfur-dependent enzyme that performs the key reduction step.
  • Butyrate kinase / butyryl-CoA:acetate CoA-transferase: Terminal enzymes releasing butyrate. E. rectale primarily uses the CoA-transferase route, which cross-feeds with acetate-producing bacteria.
  • Xylanases and other glycoside hydrolases: Enable degradation of complex plant polysaccharides (xylan, resistant starch), positioning E. rectale as a primary fermenter of dietary fiber.

Ecological Role

E. rectale is a keystone SCFA producer in the colonic ecosystem:

  • It is one of the primary colonizers of resistant starch and xylan, converting these complex carbohydrates into butyrate that fuels colonocyte metabolism.
  • It participates in cross-feeding networks: acetate produced by Bifidobacterium is consumed by E. rectale via the butyryl-CoA:acetate CoA-transferase pathway, converting it to butyrate. This syntrophic relationship means Bifidobacterium depletion indirectly reduces E. rectale butyrate output.
  • Butyrate from E. rectale serves as the primary energy source for colonocytes (supplying ~70% of their energy needs), maintains the epithelial barrier, promotes anti-inflammatory Treg differentiation, and inhibits histone deacetylases (HDACs) involved in inflammatory gene expression.

Conditions Associated

Depleted in:

  • Type 1 diabetes: Children who developed islet autoimmunity and progressed to T1D had significantly fewer E. rectale alongside F. prausnitzii and roseburia, with concurrent enrichment of LPS biosynthesis genes ([1], prospective-cohort, n=783).
  • Cardiovascular disease: Butyrate producers including E. rectale consistently depleted in CAD and heart failure. Their loss increases LPS translocation and the TMAO-producing proteolytic shift ([2], expert-opinion; [3], expert-opinion).
  • Alzheimer's disease: Decreased alongside Bacteroides hungatei and B. proteoclasticus in AD patients, while H. pylori, E. coli/Shigella, and K. pneumoniae were increased ([4], expert-opinion).
  • Hypertension: SCFA-producing bacteria including E. rectale, Faecalibacterium, and Roseburia contribute to lower blood pressure via butyrate production ([5], computational-prediction).
  • Chronic kidney disease: Depleted as part of the saccharolytic community lost in CKD, replaced by proteolytic uremic toxin producers ([6], cross-sectional).
  • Thyroid disorders: Identified as a primary colonic butyrate producer (Clostridium cluster XIVa) whose depletion disrupts SCFA-mediated thyroid immune regulation ([7], expert-opinion).

Key Studies

StudyFindingEvidence Level
[1]Depleted in T1D progressors (n=783, TEDDY cohort)Prospective cohort
[2]Depleted in CAD; loss increases LPS translocationExpert opinion
[4]Decreased in Alzheimer's diseaseExpert opinion
[7]Primary colonic butyrate producer; cluster XIVaExpert opinion
[5]SCFA production contributes to BP loweringComputational prediction

Cross-References

References (11)

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  2. Md. Mominur Rahman, Fahadul Islam, Md. Harun-Or-Rashid et al. (2022). The Gut Microbiota (Microbiome) in Cardiovascular Disease and Its Therapeutic Regulation. Frontiers in Cellular and Infection Microbiology. doi:10.3389/fcimb.2022.903570
  3. Catia Almeida, J. Guilherme Goncalves-Nobre, Diogo Alpuim Costa et al. (2023). The potential links between human gut microbiota and cardiovascular health and disease - is there a gut-cardiovascular axis?. Frontiers in Gastroenterology. doi:10.3389/fgstr.2023.1235126
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