Figure 1.

Incorporation of Kdo-N₃ into the LPS of Gram-negative bacteria. A, scheme for known core-lipid A biosynthesis in E. coli K-12 (8, 46). Dashed arrows, multiple steps. KdsB (CKS), 3-deoxy-d-manno-octulosonate cytidylyltransferase; WaaA (KdtA), Kdo transferase; WaaC, ADP-heptose:LPS heptosyltransferase I; WaaF, ADP-heptose:LPS heptosyltransferase II; Hep, heptose; IM, inner membrane; OM, outer membrane. B, scheme for Kdo-N₃ metabolic labeling: incubation of E. coli K-12 with Kdo-N₃ and copper-free click labeling with a fluorescent strained alkyne. The labeled cells can be analyzed by fluorescence microscopy and flow cytometry.