Project description:The Gram-negative, flagellated, anaerobic, crescent-shaped bacterium Selenomonas sputigena is a potential human periodontal pathogen. Information on its virulence factors and underlying pathogenicity mechanisms is scarce. Here we show for the first time that S. sputigena produces a diversely and heavily O-glycosylated flagellin C9LY14 as a major cellular protein, which carries various hitherto undescribed rhamnose- and N acetylglucosamine-linked O-glycans in the range from mono- to hexasaccharides. A comprehensive glycomic and glycoproteomic assessment revealed extensive glycan macro- and microheterogeneity on 20 unique glycopeptide species. From the multiple sites of glycosylation, five were unambiguously identified on the 437-amino acid C9LY14 protein (Thr149, Ser182, Thr199, Thr259, and Ser334). The O-glycans additionally showed modifications by methylation and acetylation. This is the first report on O-linked flagellin glycosylation in S. sputigena, revealing that C9LY14 is one of the most heavily glycosylated flagellins described to date.