Deciphering the impact of Ruminococcus gnavus cell surface glycosylation at the mucosal interface

Laplanche, Victor (2023) Deciphering the impact of Ruminococcus gnavus cell surface glycosylation at the mucosal interface. Doctoral thesis, University of East Anglia.

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The gut microbiota plays a major role in human health and an alteration in gut microbiota structure and function has been implicated in several diseases. Ruminococcus gnavus is an important member of the ‘normal’ gut microbiota and over-represented in inflammatory bowel disease. There is therefore great interest in understanding the mechanisms underpinning its interaction and communication with the host. Here we investigated the role of cell surface glycosylation in the capacity of R. gnavus strains to influence host response. We first developed a flow cytometry assay to screen cell surface glycosylation of R. gnavus E1, ATCC 29149 and ATCC 35193 strains using a range of fluorescently labelled lectins. The lectin binding profile differed between strains and depending on the carbohydrate source in the growth medium, suggesting strain-specific differences in carbohydrate epitopes on the cell surface. These were supported by bioinformatic analyses revealing differences in R. gnavus biosynthetic clusters for glucorhamnan and capsular polysaccharides. To validate these findings, the polysaccharides present on R. gnavus E1 and ATCC 35913 strains cell surface were structurally characterised by NMR and mass spectrometry, revealing a backbone composed of four α-(1,2)- and α-(1,3)-linked rhamnose and sidechains composed of one β-(1,2)-linked glucose, which differed from the previously reported structure of ATCC 29149 glucorhamnan. We next investigated how R. gnavus strains and their associated glucorhamnans influenced gut barrier function and host immune response in vitro. The data showed that R. gnavus ATCC 35913 was the most immunogenic strain using both epithelium and immune cell models. While the epithelium integrity remains unchanged, the purified glucorhamnans affected the production of cytokines by mBMDCs and triggered the activation of NF-κB pathway in reporter cells. The cytokine profile was strain-specific and varied depending on the glucorhamnan composition. Collectively these data showed that R. gnavus induces pro or anti-inflammatory responses in a strain-dependent manner, and underscores the importance of investigating the role of gut microbes at the strain level. This knowledge may be used to inform the development of diagnostic or therapeutics in R. gnavus-associated diseases.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 28 Feb 2024 09:57
Last Modified: 28 Feb 2024 09:57


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