The leading bacterial cause of diarrheal disease worldwide, with an estimated 400-500 million cases annually. C. jejuni is notable in the metallomics context for possessing a nickel-dependent [NiFe] hydrogenase essential for colonization but lacking urease -- a striking contrast with the closely related helicobacter pylori.
Nickel-Dependent Virulence
[NiFe] Hydrogenase -- No Urease
- Possesses a membrane-bound [NiFe] uptake-type hydrogenase that oxidizes H2 to generate proton motive force (PMF) for ATP synthesis [maier 2019 nickel microbial pathogenesis].
- Hydrogenase is essential for chicken colonization -- the primary animal reservoir and food safety concern. hydB deletion mutants show impaired cell division and reduced host cell interaction.
- H2 is abundant in the intestinal lumen (produced by fermentative gut microbiota), providing a reliable energy source in the microaerobic environment of the intestinal mucus layer.
- C. concisus (a related species) has the highest H2-uptake activity of any pathogenic bacterium characterized to date.
- No urease: unlike H. pylori, C. jejuni does not produce urease. It does not colonize the acidic stomach but rather the lower intestinal tract, where acid buffering is unnecessary. This makes C. jejuni a hydrogenase-only Ni-dependent pathogen.
Competitive Advantage via H2 Metabolism
- In the microaerobic intestinal mucus niche, H2 oxidation provides a competitive energy advantage over fermentation-only organisms.
- Hydrogenase activity enables C. jejuni to thrive at the epithelial surface where O2 gradients create favorable conditions for microaerobic H2-dependent respiration.
- This nickel-dependent energy metabolism supports the flagellar motility and chemotaxis that are critical for mucosal colonization.
Iron Acquisition
- C. jejuni produces enterobactin receptors (CfrA, CfrB) for siderophore piracy -- scavenging iron-loaded siderophores produced by other gut microbes rather than synthesizing its own.
- Also acquires iron via ferric enterochelin, hemin, and transferrin/lactoferrin binding proteins.
- Iron restriction is a major host defense; C. jejuni iron-uptake mutants are severely attenuated.
Clinical Significance
- Leading cause of bacterial gastroenteritis in developed countries. Primarily foodborne (undercooked poultry, unpasteurized milk).
- Causes watery or bloody diarrhea, abdominal pain, fever. Usually self-limiting but can be severe in children and immunocompromised patients.
- Guillain-Barre syndrome (GBS): C. jejuni infection is the most common antecedent of GBS, an autoimmune peripheral neuropathy. Molecular mimicry between C. jejuni lipooligosaccharide and gangliosides drives the autoimmune response.
- Reactive arthritis: post-infectious joint inflammation.
- Growing fluoroquinolone resistance complicates treatment of severe cases.
The Hydrogenase-Only Model
C. jejuni demonstrates that [NiFe] hydrogenase alone -- without urease -- can be sufficient for nickel-dependent pathogenesis when the ecological niche does not require acid neutralization. This contrasts with helicobacter pylori (urease + hydrogenase), salmonella typhimurium (four hydrogenases), and shigella flexneri (hydrogenase for phagolysosomal acid combat). The pathogen's niche determines which Ni-enzymes are essential.
Connections
- hydrogenase -- [NiFe] hydrogenase essential for chicken colonization
- urease -- notably absent; contrasts with H. pylori
- nickel -- essential cofactor for hydrogenase
- iron -- acquired via siderophore piracy and dedicated transporters
- metal dependent virulence -- hydrogenase-only Ni-dependent virulence model
- helicobacter pylori -- closely related but with very different Ni-enzyme complement
- gut metal microbiome -- H2 availability in the gut lumen enables hydrogenase function
- nutritional immunity -- host iron restriction limits C. jejuni colonization