Host Mucin Is Exploited by Pseudomonas aeruginosa To Provide Monosaccharides Required for a Successful Infection

Abstract

One of the primary functions of the mucosal barrier, found lining epithelial cells, is to serve as a first-line of defense against microbial pathogens. The major structural components of mucus are heavily glycosylated proteins called mucins. Mucins are key components of the innate immune system as they aid in the clearance of pathogens and can decrease pathogen virulence. It has also been recently reported that individual mucins and derived glycans can attenuate the virulence of the human pathogen Pseudomonas aeruginosa. Here, we show data indicating that mucins not only play a role in host defense but that they can also be subverted by P. aeruginosa to cause disease. We found that the mucin MUL-1 and mucin-derived monosaccharides N-acetyl-galactosamine and N-acetylglucosamine are required for P. aeruginosa killing of Caenorhabditis elegans. We also found that the defective adhesion of P. aeruginosa to human lung alveolar epithelial cells, deficient in the mucin MUC1, can be reversed by the addition of individual monosaccharides. The monosaccharides identified in this study are found in a wide range of organisms where they act as host factors required for bacterial pathogenesis. While mucins in C. elegans lack sialic acid caps, which makes their monosaccharides readily available, they are capped in other species. Pathogens such as P. aeruginosa that lack sialidases may rely on enzymes from other bacteria to utilize mucin-derived monosaccharides. IMPORTANCE One of the first lines of defense present at mucosal epithelial tissues is mucus, which is a highly viscous material formed by mucin glycoproteins. Mucins serve various functions, but importantly they aid in the clearance of pathogens and debris from epithelial barriers and serve as innate immune factors. In this study, we describe a requirement of host monosaccharides, likely derived from host mucins, for the ability of Pseudomonas aeruginosa to colonize the intestine and ultimately cause death in Caenorhabditis elegans. We also demonstrate that monosaccharides alter the ability of bacteria to bind to both Caenorhabditis elegans intestinal cells and human lung alveolar epithelial cells, suggesting that there are conserved mechanisms underlying host-pathogen interactions in a range of organisms. By gaining a better understanding of pathogen-mucin interactions, we can develop better approaches to protect against pathogen infection.

Impact of diet and the bacterial microbiome on the mucous barrier and immune disorders

“…74,75 Similarly, mucins in the lung and oral cavity, from where bacteria migrate to the lower respiratory tract, 2 inhibit biofilm formation and downregulate toxins and other virulence factors of pathogenic taxa, such as Pseudomonas aeruginosa, preventing their outgrowth and dominance and thereby promoting community diversity. [76][77][78] These protective effects may be subverted, as P aeruginosa can utilize MUC1 for adherence 79 and reside in the mucus to evade exposure to antibiotics, particularly with mucus hypersecretion such as in cystic fibrosis. 80,81 Many bacteria in the GI and respiratory tracts utilize the mucous barrier as a carbon source and are highly adapted to this microenvironment.…”

Interspecies bacterial competition regulates community assembly in the C. elegans intestine

“…Furthermore, the C. elegans gut environment filters the larger bacterial pool found in natural feeding substrates, leading to the assembly of a core microbiota [31,32]. Such environmental filtering can occur via behavioral food avoidance [33], ingestion rates [34,35], and host mucins [36], among other factors [7,26]. Recent reports have suggested that the worm's innate immunity [37,38] and microbe-microbe interactions [39] play a dominant role in the C. elegans microbiota assembly, but an experimental comparison of the many forces in play is still lacking.…”

Commercial porcine gastric mucin contributes to variation in production of small molecule virulence factors by Pseudomonas aeruginosa when cultured in different formulations of artificial sputum medium

“…The mucin concentration of CF sputum ranges from 16-30 mg/mL (1). In the lung, mucin is a source of nutrients for inhabiting microbes (2, 87, 88) and also is involved in microbial adhesion (87), aggregation (89, 90) and dispersion (83).…”

“…25,108 The altered biophysical properties of pulmonary mucus in CF contributes to the establishment of chronic infections by pathogens, including P. aeruginosa. [109][110][111] Due to its importance in CF pathogenesis, inclusion of mucin in ASM is critical to fully replicating the in vivo nutritional 26,112,113 and structural 112,[114][115][116] CF pulmonary environment. 13,116,117 However, despite the limitations associated with altered physical and chemical properties of the mucins associated with the purification process and inclusion of a number of mucin-bound impurities [118][119][120] , the most economical choice is commercial porcine gastric mucin (PGM), which is often used as a component of ASM without further purification.…”