A genetic locus in the gut microbeBacteroides thetaiotaomicronencodes activities consistent with mucin-O-glycoprotein processing and plays a critical role inN-acetylgalactosamine metabolism

Abstract

AbstractIt is increasingly appreciated that members of the gut microbiota are key modulators of human health and the status of major diseases including cancer, diabetes and inflammatory bowel disease. Central to their survival is the ability to metabolise complex dietary and host-derived glycans including intestinal mucins. The latter are critical components of the gut epithelium glycocalyx and mucus barriers, essential for microbiota-gut homeostasis and protection from infections by pathogens. The prominent and model human gut microbeBacteroides thetaiotaomicron (B. theta)is a versatile and highly efficient complex glycan degrader thanks to the expansion of gene clusters termed polysaccharide utilisation loci (PULs) in its genome. While the mechanisms for several singular dietary glycan-induced PULs have been elucidated, studies on the 16-18 mucin-induced PULs inB. thetasignificantly lag behind. A combination of the scale and complexity ofB. thetatranscriptomic response to mucins and complex glycan configurations of mucins represent major hurdles for the functional characterisation of the mucin induced PULs. As a result, there is very limited knowledge on how mucin metabolism is coordinated inB. thetaand what specific PULs, genes and metabolites are critical for mucin-B. theta,and more generally mucin-microbiota interactions and their importance in microbiota-gut homeostasis. Here we show that a mucin inducible PUL BT4240-50, (i) encodes activities consistent with a machinery that couples the processing of mucin-O glycan glycoproteins with the metabolism ofN-acetylgalactosamine (GalNAc), an abundant mucin O-glycan sugar; (ii) is important for competitive growth on mucinsin-vitro; (iii) encodes a key kinase enzyme (BT4240) that is critical for GalNAc metabolism and (iv) has related PULs encoded by a range of prominentBacteroidesspecies in the human gut. Furthermore, BT4240 kinase was also critical for glycosaminoglycan metabolism, thus extending the PULs function beyond mucins. Our work advances our understanding of the vital metabolic processes that govern mucosal glycoprotein metabolism and by implication, a key aspect of host-microbiota interactions at mucosal surfaces and highlight GalNAc as a key metabolite targeted for competitive growth.