Breaking down barriers: is intestinal mucus degradation by beneficial or harmful?

is a specialized mucin-degrading bacterium that plays a pivotal role in gut health and disease. This review examines the dualistic nature of mucin degradation, exploring its potential benefits and risks. As a mucin specialist, uses glycosyl hydrolases and mucinases to degrade mucins, producing metabolites like short-chain fatty acids (SCFAs), branched-chain fatty acids (BCFAs), succinate, and other compounds. These metabolites benefit host health and cross-feed other commensal microbes, such as butyrate producers. levels are inversely correlated with several disease states, such as obesity, diabetes, and inflammatory states, and administration of has been found by several groups to restore and maintain gut homeostasis. However, under certain conditions, such as low dietary fiber or conditions with an altered gut microbiota, excessive mucin degradation by can compromise the mucus barrier, increasing susceptibility to inflammation, infection, and pathogenic overgrowth. Elevated levels have been associated with various diseases and medications, including graft versus host disease (GVHD) and irradiation, and shown to exacerbate infections by enteric pathogens. The context-dependent effects of and mucin degradation underscore the need for a nuanced understanding of its interactions with the host and microbial community. This review aims to provide a balanced perspective on the implications of gut microbial mucus degradation, highlighting that it can be good, and it can be bad depending on the context.