O-antigen is a part of the lipopolysaccharide present in the outer membrane of Gram-negative bacteria, which is essential for the full function of the microorganisms and is related to bacterial virulence. Salmonella enterica and Escherichia coli are taxonomically closely related species. In this study, the O-antigen structures of S. enterica O16, O38 and E. coli O11 were determined. It was found that S. enterica O38 and E. coli O21 share the O-antigen structure, whereas those of S. enterica O16 and E. coli O11 are closely related differing only in the presence of a lateral glucose residue and O-acetylation of a mannose residue in the former. The O-antigen gene clusters of S. enterica O16, O38 and E. coli O11 were sequenced and analyzed together with that of E. coli O21 retrieved from Genbank. For each S. enterica/E. coli pair, they were found to contain the same set of genes organized in the same manner and sharing 56% to 78% overall DNA identity. These data suggest that the O-antigen gene clusters of each pair studied originated from a common ancestor, as reported for a number of other known E. coli/S. enterica pairs having identical or closely related O-antigen structures. It has become thus evident that in past the degree of relatedness between the O-antigens of S. enterica and E. coli was underestimated.

Escherichia coli, Salmonella enterica, O-antigen gene cluster, Glycomics, O-antigen diversity

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,6,2	Ac	176.1	23.3
3,3,6,3	aLFucp	101.5	69.2	71.3	73.2	69.0	16.8
3,3,6	aDGalpN	98.9	50.6	75.9	73.6	72.8	62.2
3,3	aDManp	104.0	71.5	72.1	67.8	73.2	67.0
3	aLFucp	102.7	68.8	79.2	73.3	68.5	16.7
2	Ac	176.7	24.0
	bDGalpN	101.3	53.7	79.8	69.8	77.2	62.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,6,2	Ac	-	2.02
3,3,6,3	aLFucp	5.02	3.76	3.76	3.85	3.98	1.24
3,3,6	aDGalpN	4.86	4.52	4.13	4.37	4.06	3.75-3.79
3,3	aDManp	5.10	4.09	3.90	3.92	3.89	3.61-4.08
3	aLFucp	5.00	3.83	3.98	3.83	4.15	1.19
2	Ac	-	2.09
	bDGalpN	5.05	3.94	3.89	3.96	3.52	3.75-3.80


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,6,2	Ac		23.3/2.02
3,3,6,3	aLFucp	101.5/5.02	69.2/3.76	71.3/3.76	73.2/3.85	69.0/3.98	16.8/1.24
3,3,6	aDGalpN	98.9/4.86	50.6/4.52	75.9/4.13	73.6/4.37	72.8/4.06	62.2/3.75-3.79
3,3	aDManp	104.0/5.10	71.5/4.09	72.1/3.90	67.8/3.92	73.2/3.89	67.0/3.61-4.08
3	aLFucp	102.7/5.00	68.8/3.83	79.2/3.98	73.3/3.83	68.5/4.15	16.7/1.19
2	Ac		24.0/2.09
	bDGalpN	101.3/5.05	53.7/3.94	79.8/3.89	69.8/3.96	77.2/3.52	62.4/3.75-3.80

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*O[C@H]1[C@@H](CO)O[C@H](OC[C@H]2O[C@H](O[C@H]3[C@H](O)[C@H](O[C@@H]4[C@@H](NC(C)=O)[C@H](*)O[C@H](CO)[C@@H]4O)O[C@@H](C)[C@H]3O)[C@@H](O)[C@@H](O)[C@@H]2O)[C@H](NC(C)=O)[C@H]1O[C@@H]1O[C@@H](C)[C@@H](O)[C@@H](O)[C@@H]1O

860.813 g/mol (C₃₄H₅₆R₂N₂O₂₃, R = next and previous repeats, not counted in mol weight)