C. difficile S-layer and glycosylation genetic loci. The S-layer loci of strains 630 (A) and Ox247 (B) show the relative locations of slpA and surrounding genes. Insertion of a 24-kb locus harboring a putative glycosylation machinery is shown in Ox247 and in more detail in C. The ORFs of the glycosylation locus in C are numbered according to Ref. 11 and are color-coded to indicate putative function: green, glycosyltransferases; purple, glycosyltransferases; red, ABC transporter; pink, rhamnose biosynthesis; orange, oligosaccharide ligase; white, no function predicted.