<i>Giardia</i> spp.-induced microbiota dysbiosis disrupts intestinal mucin glycosylation

Infection with the protozoan parasite <i>Giardia duodenalis</i> (syn. <i>intestinalis</i>, <i>lamblia</i>) has been associated with intestinal mucus disruptions and microbiota dysbiosis. The mechanisms remain incompletely understood. Mucus consists primarily of densely glycosylated mucin glycoproteins. Mucin <i>O</i>-glycans influence mucus barrier properties and mucin-microbe interactions and are frequently altered during disease. In this study, we observed time-dependent and regiospecific alterations to intestinal mucin glycosylation patterns and the expression of mucin-associated glycosyltransferase genes during <i>Giardia</i> infection. Glycosylation alterations were observed in <i>Giardia</i>-infected mice in the upper small intestine, the site of parasite colonization, and in the distal colon, where active trophozoites were absent. Alterations occurred as early as day 2 post-infection and persisted in mice after parasite clearance. We also observed small intestinal goblet cell hyperplasia and thinning of the distal colon mucus barrier during early infection, and microbiota alterations and altered production of cecal SCFAs. <i>Giardia</i>-induced alterations to mucin glycosylation were at least in part dependent on microbiota dysbiosis, as transplantation of a dysbiotic mucosal microbiota collected from <i>Giardia</i>-infected mice recapitulated some alterations. This study describes a novel mechanism by which <i>Giardia</i> alters intestinal mucin glycosylation, and implicates the small intestinal microbiota in regulation of mucin glycosylation patterns throughout the gastrointestinal tract.