MS/MS spectra from the intact LOSs from C. jejuni wild-type 01/51 (A) and C. jejuni 01/51 Δcj1136 (B). The intact LOS of C. jejuni wild-type 01/51 ions m/z 1108 and truncated LOS of cj1136 mutant ions m/z 1151 were further analyzed by MS/MS. The major cluster of molecular ions at m/z 1062.4 corresponds to lipid A in the LOSs from both wild-type 01/51 and its cj1136 mutant. Neu5Ac, sialic acid; KDO, 2-keto 3-deoxy-octulosonic acid, P, phosphate; PEtn, phosphoethanolamine; COS, core oligosaccharide; tCOS, truncated core oligosaccharide; Hex, hexose; Hep, heptose; Gly, glycine. The composition of COS corresponds to Neu5Ac1-HexNAc1-Hex5-Gly1-Hep2-PEtn1-KDO2, and that of tCOS corresponds to Hex2-Gly1-Hep2-PEtn1-KDO2.