Microbial Metabolites

Overview

Microbial metabolites are the chemical products of microbial metabolism that act as signaling molecules, nutrients, or toxins within and beyond the gut. They are the functional output of the microbiome — the mechanism by which microbial composition translates into host physiology and disease. With 418 source mentions across the vault, metabolites are the most frequently discussed functional concept in WikiBiome.

Major Metabolite Classes

Short-Chain Fatty Acids (SCFAs)

The most studied beneficial microbial metabolites. See short chain fatty acids, butyrate, propionic acid.

  • Butyrate: Colonocyte fuel, HDAC inhibitor, barrier protector, anti-inflammatory via GPR109A.
  • Propionate: Hepatic gluconeogenesis modulator; anti-inflammatory.
  • Acetate: Most abundant SCFA; appetite regulation, peripheral metabolism.

Trimethylamine N-Oxide (TMAO)

Microbial metabolism of choline/carnitine → TMA → hepatic oxidation → TMAO. Pro-atherosclerotic. See dedicated page.

Bile Acid Metabolites

Bacterial bile salt hydrolases (BSH) deconjugate primary bile acids; 7α-dehydroxylases convert to secondary bile acids. See bile acid metabolism.

Tryptophan Metabolites

Microbial tryptophan metabolism produces indoles (indoles), kynurenine pathway intermediates, and serotonin precursors. These activate AhR (aryl hydrocarbon receptor) and modulate gut brain axis signaling.

Neuroactive Metabolites

  • GABA: Produced by Lactobacillus, Bifidobacterium via glutamate decarboxylase.
  • serotonin: ~95% of body serotonin produced in the gut, modulated by microbial metabolites.
  • Dopamine precursors: Microbial tyrosine decarboxylase.

Uremic Toxins

  • p-Cresol sulfate, indoxyl sulfate: Microbial metabolites that accumulate in CKD, driving cardiovascular and neurological complications.

Gaseous Metabolites

  • hydrogen sulfide: Produced by sulfate-reducing bacteria; cytotoxic at high concentrations, signaling molecule at low concentrations.
  • H₂: Substrate for nickel-dependent NiFe-hydrogenases in pathogenic Enterobacteriaceae.

Metal-Metabolite Interface

Microbial metabolites and metals interact bidirectionally:

  • SCFA production requires iron-sulfur cluster enzymes (butyryl-CoA dehydrogenase) — metal availability directly affects metabolite output.
  • Siderophores are themselves metabolites — iron-chelating molecules that shape both microbial ecology and host iron homeostasis.
  • Metal exposure alters metabolite profiles: Cadmium exposure shifts fecal metabolomics, reducing beneficial SCFAs and increasing uremic toxin precursors.

Cross-References

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