Gilthead seabream (Sparus aurata) mucus core O-glycosylation changes in Enteromyxum leei parasitized intestine.

The gilthead seabream, Sparus aurata, is an important fish within the aquaculture industry. Enteromyxum leei causes chronic enteritis, resulting in reduced nutrient absorption and growth, cachexia and/or death of the fish. There are currently no applied treatments for this disease. To investigate the first barrier pathogens encounter, the mucus, we characterized the gilthead seabream intestinal mucus glycome from five control and five E. leei infected gilthead seabream using mass spectrometry and investigated the link between identified glycans and infection parameters, gene expression and microbiome. We identified 110 O-glycans and 9 N-glycans, whereof the latter constituted 12% of the mucus glycome and did not differ between infected and control fish. The most pronounced O-glycome change detected was decreased levels of Core 4 O-glycans in E. leei infected intestines. The variance of the O-glycosylation was also larger in infected fish compared to the control fish. The relative abundance of Core 4 glycans correlated with the expression levels of muc13 and imuc as well as with key genes in type I immune responses. Furthermore, the decrease in Core 4 glycans was also linked to decreased abundances of Streptococcus, Staphylococcus and Corynebacterium. This work presents the most probable key players in these complex interactions and provides a platform for further studies aiming to identify how the mucosal glycosylation protects the fish from infection.