Thesis Defence: Role of Mucin-Type O-Glycans in Regulating Metabolic and Functional Responses of Phocaeicola Vulgatus

Madison Dirks, supervised by Dr. Kirk Bergstrom, will defend their thesis titled “Role of Mucin-Type O-Glycans in Regulating Metabolic and Functional Responses of Phocaeicola Vulgatus” in partial fulfillment of the requirements for the degree of Master of Science in Biology.

An abstract for Madison Dirks’ thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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Abstract

Phocaeicola vulgatus (formerly Bacteroides vulgatus) is considered a commensal symbiont in most individuals. However, P. vulgatus has been shown to promote colitis in both humans with inflammatory bowel disease (IBD), and in genetically susceptible mouse models through its proteolytic activity. IBD, which includes Crohn’s disease (CD), and ulcerative colitis (UC), is characterized by chronic intestinal inflammation, and a disrupted mucus barrier. The mucus layer, known to be enriched in O-glycans, plays a key role in maintaining host-microbe separation as well as intestinal homeostasis. However, the extent to which healthy versus IBD mucus shapes P. vulgatus interactions, and its colitis potential remains poorly understood. We found P. vulgatus grew well on O-glycans derived from healthy, and CD mucin-2 (MUC2) as sole carbon sources which was comparable to glucose. RNASeq of P. vulgatus grown on the human MUC2 glycans showed robust induction of carbohydrate-active enzymes from various polysaccharide utilization loci directed against mucin-type O-glycans, consistent with predicted key mucin-utilization genes. Interestingly, compared to glucose alone, growth on O-glycans was associated with a reduction in the expression of several peptidases, suggesting that the diversity of glycans influences allocation towards their utilization, and away from protease usage. However, a few proteases were induced compared to glucose, and may account for some activity against beta-casein. Inoculation of wild-type mice with P. vulgatus showed dense localization of the niche layer of MUC2, while the barrier layer prevented contact with the mucosa. Notably, niche localization and barrier function was lost in mice lacking both core 1 and 3-derived O-glycans. This all potentially indicates that glycans and organized mucin contribute to P. vulgatus mucus establishment and mucosal separation. Mice found to contain the commensal protozoan Tritrichomonas muris were found to have impaired P. vulgatus establishment, likely through bacterial grazing. Collectively, these results demonstrate P. vulgatus exhibits robust growth on healthy and CD human O-glycans, at the expense of peptidase expression. In vivo, complex O-glycans support niche establishment without barrier degradation; their loss disrupts colonization, leading to mucus breakdown and revealing glycan-mediated host-microbe interactions. These studies provide novel insight into P. vulgatus interactions with colonic mucus.