Bacterial constipation: Mucin-degrading intestinal commensal bacteria cause constipation.

A. muciniphila and B. thetaiotaomicron were increased in constipated patients with Parkinson's disease (PD) and chronic idiopathic constipation (CIC).

• Both mucin-degrading gut commensals were elevated in two distinct constipation patient populations: PD patients and CIC patients.
• The association was observed in human clinical cohorts, not just animal models.
• A. muciniphila alone was not correlated with constipation in humans, suggesting the cooperative presence of both bacteria is required.

Gnotobiotic mice co-colonized with both A. muciniphila and B. thetaiotaomicron developed constipation, whereas mice colonized with either bacterium alone did not.

• Single colonization with A. muciniphila alone did not produce constipation phenotype.
• Single colonization with B. thetaiotaomicron alone did not produce constipation phenotype.
• Co-colonization with both bacteria was necessary and sufficient to induce constipation in gnotobiotic mice.
• This cooperative induction supports the clinical observation that A. muciniphila alone does not correlate with constipation in humans.

Fecal mucins carry terminal sulfates whereas gastric mucins do not, implicating colonic mucin sulfate catabolism as a site-specific mechanism.

• The differential sulfation between fecal and gastric mucins was identified as relevant to the colonic site of constipation pathogenesis.
• This finding directed the mechanistic investigation toward sulfatase activity as the key enzymatic function.

Fecal transcriptome analysis of gnotobiotic mice suggested a sulfatase-dependent mechanism underlying bacterially induced constipation.

• Transcriptomic profiling of gnotobiotic mouse feces provided evidence pointing to sulfatase-dependent pathways.
• This finding prompted generation of an anaerobic sulfatase-maturating enzyme (anSME)-deficient B. thetaiotaomicron strain.
• anSME is required for B. thetaiotaomicron to catabolize the terminal sulfates of mucins.

An anSME-deficient B. thetaiotaomicron strain that cannot catabolize terminal sulfates of mucins ameliorated constipation in co-colonized gnotobiotic mice.

• A genetically engineered anaerobic sulfatase-maturating enzyme (anSME)-deficient mutant of B. thetaiotaomicron was generated.
• In the absence of anSME activity, constipation was ameliorated when co-colonized with A. muciniphila in gnotobiotic mice.
• This provides direct causal evidence that sulfatase activity of B. thetaiotaomicron is required for the constipation phenotype.

Intestinal bacteria other than B. thetaiotaomicron that also catabolize mucin sulfates may substitute for B. thetaiotaomicron in patients with constipation.

• Multiple intestinal bacteria possess sulfatase activity capable of catabolizing mucin sulfates.
• This functional redundancy among sulfatase-expressing bacteria may explain why constipation correlates with the functional capacity rather than specific bacterial species.
• This finding broadens the proposed mechanism beyond a single bacterium to a community-level functional phenotype.

The proposed mechanism of 'bacterial constipation' involves cooperative degradation of colonic mucins by sulfatases and glycosylases, reducing lubrication and inducing fecal dehydration.

• A. muciniphila contributes glycosylase activity while B. thetaiotaomicron contributes sulfatase activity to cooperatively degrade colonic mucins.
• Mucin degradation is proposed to reduce colonic lubrication.
• Reduced lubrication leads to fecal dehydration, the proximate cause of constipation.
• Targeting microbial sulfatase activity is proposed as a promising therapeutic approach for patients with bacterial constipation.