Experimentally confirmed enzymatic steps (in green) in T. forsythia strains ATCC 43037 (left) and FDC 92A2/UB4 (right) corresponding to the CMP-Pse and CMP-Leg biosynthetic pathways as elucidated in H. pylori and C. jejuni, respectively (Schoenhofen et al. 2006b, Schoenhofen et al. 2009). In T. forsythia, pathways will deviate at some point to produce the unique NulO derivatives found in our strains, such as Pse5Am7Gra. These deviations would be anticipated to occur either within the NulO biosynthetic pathway or post CMP-NulO biosynthesis. Red, blue and orange highlight enzymatic steps that introduce the stereochemical differences between the two pathways and also indicate the positions altered for both hexose intermediates and final NulO. The assignment of roman numerals to each compound is consistent with label designations found throughout the text. Subscripts “P” and “L” indicate intermediates from the CMP-Pse and CMP-Leg biosynthesis pathway, respectively. For simplicity, all sugars except for the NulOs are shown in 4C1 form. This figure is available in black and white in print and in color at Glycobiology online.