While it is now evident that the two Bacteroidales species Bacteroides fragilis and Tannerella forsythia both have general O-glycosylation systems and share a common glycosylation sequon, the ability of these organisms to glycosylate a protein native to the other organism has not yet been demonstrated. Here, we report on the glycosylation of heterologous proteins between these two organisms. Using genetic tools previously developed for Bacteroides species, two B. fragilis model glycoproteins were expressed in the fastidious anaerobe T. forsythia and the attachment of the known T. forsythia O-glycan to these proteins was demonstrated by liquid chromatography electrospray ionization tandem mass spectrometry. Likewise, two predominant T. forsythia glycoproteins were expressed in B. fragilis and glycosylation with the B. fragilis O-glycan was confirmed. Purification of these proteins from B. fragilis allowed the preliminary characterization of the previously uncharacterized B. fragilis protein O-glycan. Based on mass spectrometric data, we show that the B. fragilis protein O-glycan is an oligosaccharide composed of nine sugar units. Compositional and structural similarities with the T. forsythia O-glycan suggest commonalities in their biosynthesis. These data demonstrate the feasibility of exploiting these organisms for the design of novel glycoproteins.

Cell surface glycosylation is an important element in defining the life of pathogenic bacteria. Tannerella forsythia is a Gram-negative, anaerobic periodontal pathogen inhabiting the subgingival plaque biofilms. It is completely covered by a two-dimensional crystalline surface layer (S-layer) composed of two glycoproteins. Although the S-layer has previously been shown to delay the bacterium's recognition by the innate immune system, we characterize here the S-layer protein O-glycosylation as a potential virulence factor. The T. forsythia S-layer glycan was elucidated by a combination of electrospray ionization-tandem mass spectrometry and nuclear magnetic resonance spectroscopy as an oligosaccharide with the structure 4-Me-β-ManpNAcCONH 2-(1→3)- [Pse5Am7Gc-(2→4)-]-β-ManpNAcA-(1→4)-[4- Me-α-Galp- (1→2)-]-α-Fucp-(1→4)-[-α-Xylp-(1→3)- ]-β-GlcpA-(1→3)- [-β-Digp-(1→2)-]-α-Galp, which is O-glycosidically linked to distinct serine and threonine residues within the threeamino acid motif (D)(S/T)(A/I/L/M/T/V) on either S-layer protein. This S-layer glycan obviously impacts the life style of T. forsythia because increased biofilm formation of an UDP-N-acetylmannosaminuronic acid dehydrogenase mutant can be correlated with the presence of truncated S-layer glycans. We found that several other proteins of T. forsythia are modified with that specific oligosaccharide. Proteomics identified two of them as being among previously classified antigenic outer membrane proteins that are up-regulated under biofilm conditions, in addition to two predicted antigenic lipoproteins. Theoretical analysis of the S-layer O-glycosylation of T. forsythia indicates the involvement of a 6.8-kb gene locus that is conserved among different bacteria from the Bacteroidetes phylum. Together, these findings reveal the presence of a protein O-glycosylation system in T. forsythia that is essential for creating a rich glycoproteome pinpointing a possible relevance for the virulence of this bacterium.