LAUSR

Flavobacterium johnsoniae is a Gram-negative bacterium that is found in soil and water. It is frequently used as a model species for studying gliding motility and the T9SS. ABSTRACT Flavobacterium johnsoniae is a free-living member of the Bacteroidota phylum that is found in soil and water. It is frequently used as a model species for studying a type of gliding motility dependent on the type IX secretion system (T9SS). O-Glycosylation has been reported in several Bacteroidota species, and the O-glycosylation of S-layer proteins in Tannerella forsythia was shown to be important for certain virulence features. In this study, we characterized the O-glycoproteome of F. johnsoniae and identified 325 O-glycosylation sites within 226 glycoproteins. The structure of the major glycan was found to be a hexasaccharide with the sequence Hex–(Me-dHex)–Me-HexA–Pent–HexA–Me-HexNAcA. Bioinformatic localization of the glycoproteins predicted 68 inner membrane proteins, 60 periplasmic proteins, 26 outer membrane proteins, 57 lipoproteins, and 9 proteins secreted by the T9SS. The glycosylated sites were predominantly located in the periplasm, where they are postulated to be beneficial for protein folding/stability. Six proteins associated with gliding motility or the T9SS were demonstrated to be O-glycosylated. IMPORTANCE Flavobacterium johnsoniae is a Gram-negative bacterium that is found in soil and water. It is frequently used as a model species for studying gliding motility and the T9SS. In this study, we characterized the O-glycoproteome of F. johnsoniae and identified 325 O-glycosylation sites within 226 glycoproteins. The glycosylated domains were mainly localized to the periplasm. The function of O-glycosylation is likely related to protein folding and stability; therefore, the finding of the glycosylation sites has relevance for studies involving expression of the proteins. Six proteins associated with gliding motility or the T9SS were demonstrated to be O-glycosylated, which may impact the structure and function of these components.