Gut microbe’s protective coating links intestinal colonization to lower inflammation

The human gut harbors more than 40 trillion bacteria assembled into complex communities collectively known as the gut microbiota, which is closely linked to human health and disease. Mediterraneibacter gnavus (formerly Ruminococcus gnavus) is a commensal bacterium in the Lachnospiraceae family that is normally found in healthy individuals.

However, it is frequently enriched in patients with inflammatory bowel diseases (such as Crohn’s disease), and its abundance has been correlated with disease severity. Despite the clinical relevance of M. gnavus, the molecular mechanisms underlying its intestinal colonization and strain-dependent effects on host inflammation remain poorly understood, largely because this bacterium presents technical challenges for genetic manipulation.

Tools to probe a difficult microbe

Researchers at University of Tsukuba have developed a suite of molecular genetic tools specifically for characterizing M. gnavus, including an E. coli-M. gnavus shuttle vector, inducible gene expression systems, fluorescent reporters and systems for gene disruption and deletion. Notably, these tools were applicable not only to M. gnavus but also to other common human commensals in the Lachnospiraceae family.

The work is published in the journal Nature Communications.

A protective coating with consequences

Researchers identified a gene cluster responsible for capsular polysaccharides (CPS) biosynthesis and demonstrated the importance of CPS production in competitive intestinal colonization in germ-free mouse models. CPS forms a protective layer on the bacterial surface and participates in host-microbe interactions.

Notably, CPS production was inversely correlated with inflammatory activity. Mutant strains lacking CPS induced stronger inflammatory responses, whereas mice colonized with CPS-deficient strains exhibited more severe inflammation.

Comparative genomic analyses further revealed that CPS-related gene clusters tend to occur more frequently in strains isolated from healthy individuals than in those isolated from patients with Crohn’s disease.

Clues for future probiotic design

This study establishes a platform for the functional analysis of gut bacteria that present difficulties for genetic manipulation. The findings advance understanding of the influence of specific bacterial genes on host-microbe interactions.

Furthermore, the results may help elucidate the mechanisms underlying inflammatory diseases and facilitate the development of next-generation probiotic microbes that promote intestinal homeostasis.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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