Schematic structure of B. abortus outer membrane showing the LPS and NH. The O polysaccharide and native hapten (NH) are unbranched linear homopolymers of α-1,2-linked 4,6-dideoxy-4-formamido-d-mannopyranosyl units (N-formyl-perosamine) with an average chain length of 96 to 100 glycosyl subunits (28). While the NH is not directly bound to the lipid membrane, the O polysaccharide is linked to a core bifurcating oligosaccharide composed of βGlcN-6-βGlcN-4-βGlcN(-6-βGlcN)-3-αMan(-6-αGlc)-5-KDO1(−1-KDO1)-lipid A immersed in the outer membrane. Branching from KDO2 is αPerNFo-(-2PerNFo)n-2PerNFo-2-αMan-3-αMan-3-βQuiNAc-4-βGlc-4-KDO2-4-KDO2 (59). The KDO1 is linked to the lipid A composed of a backbone of diaminoglucose (DAG) disaccharide, substituted with phosphates (P) and amide and ester-linked long-chain saturated (C16:0 to C18:0) and hydroxylated (3-OH-C12:0 to 29-OH-C30:0) fatty acids (17, 60). The lipid A is bound to the outer membrane. KDO, ketodeoxyoctulosonic acid; Man, mannose; QuiN, acetyl-quinovosamine; Glc, glucose (Glc); PerNFo, N-formyl-perosamine. The ΔwadC mutation precludes the incorporation of the βGlcN-6-βGlcN-4-βGlcN(-6-βGlcN)-3-αMan(-6-αGlc)-oligosaccharide to the KDO1 (marked by a gray area) while the Δper mutation precludes the incorporation of αPerNFo-(-2PerNFo)n-2PerNFo-homopolymer (61).