Escherichia coli includes clonal groups of both commensal and pathogenic strains, with some of the latter causing serious infectious diseases. O antigen variation is current standard in defining strains for taxonomy and epidemiology, providing the basis for many serotyping schemes for Gram-negative bacteria. This review covers the diversity in E. coli O antigen structures and gene clusters, and the genetic basis for the structural diversity. Of the 187 formally defined O antigens, six (O31, O47, O67, O72, O94 and O122) have since been removed and four (O14, O34, O89 and O144) strains do not produce any O antigen. Therefore, structures are presented for 176 of the 181 E. coli O antigens, some of which include subgroups. Most (93%) of these O antigens are synthesized via the Wzx/Wzy pathway, 11 via the ABC transporter pathway, with O20, O57 and O60 still uncharacterized due to failure to find their O antigen gene clusters. Biosynthetic pathways are given for 38 of the 49 sugars found in E. coli O antigens, and several pairs or groups of the E. coli antigens that have related structures show close relationships of the O antigen gene clusters within clades, thereby highlighting the genetic basis of the evolution of diversity.

structure, O antigen, Escherichia coli, gene cluster, serogroup, diversity

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

723.682 g/mol (C₂₉H₄₅R₂N₃O₁₈, R = next and previous repeats, not counted in mol weight)

On mild acid degradation of the lipopolysaccharide of Escherichia coli O61, the O-polysaccharide chain was cleaved at a linkage of 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-D-galacto-non-2-ulosonic acid (di-N-acetyl-8-epilegionaminic acid, 8eLeg5Ac7Ac). The resultant trisaccharide, an O-deacylated lipopolysaccharide and an O-deacetylated trisaccharide derived from the latter were studied by sugar analyses along with 1H and 13C NMR spectroscopy, and the following structure of the O-polysaccharide was established: [formula, see text].

Lipopolysaccharide, O-antigen, Escherichia coli, nonulosonic acid, bacterial polysaccharide structure, 8-epilegionaminic acid

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
3,4,5	Ac
3,4,7	Ac
3,4,8	70%Ac	?	21.9
3,4	aX8eLegp	?	101.9	37.6	72.4	51.7	75.2	55.0	69.5	20.2
3	bDGlcp	105.8	74.3	76.2	73.2	76.2	61.3
2	Ac
	aDGalpN	94.6	49.4	79.2	70.0	73.2	62.2


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
3,4,5	Ac
3,4,7	Ac
3,4,8	70%Ac	-	2.00
3,4	aX8eLegp	-	-	1.63-2.78	3.72	3.72	3.86	3.91	3.98	1.22
3	bDGlcp	4.45	3.27	3.51	3.98	3.41	3.76-3.84
2	Ac
	aDGalpN	5.01	3.34	3.70	4.17	3.72	3.69-3.71


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
3,4,5	Ac
3,4,7	Ac
3,4,8	70%Ac		21.9/2.00
3,4	aX8eLegp			37.6/1.63-2.78	72.4/3.72	51.7/3.72	75.2/3.86	55.0/3.91	69.5/3.98	20.2/1.22
3	bDGlcp	105.8/4.45	74.3/3.27	76.2/3.51	73.2/3.98	76.2/3.41	61.3/3.76-3.84
2	Ac
	aDGalpN	94.6/5.01	49.4/3.34	79.2/3.70	70.0/4.17	73.2/3.72	62.2/3.69-3.71

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

723.682 g/mol (C₂₉H₄₅R₂N₃O₁₈, R = next and previous repeats, not counted in mol weight)

Recent data on the natural occurrence, chemistry, and biochemistry of C8 and C9 aldulosonic acids (3-deoxy-d-manno-oct-2-ulosonic acid, sialic acids, N-acyl derivatives of 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acids, and some others) as well as on the structures and biological significance of bacterial glycans containing these higher acidic monosaccharides are summarized.

structure, Bacterial, glycan, aldulosonic acid, higher acidic monosaccharides, sialic acids

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

723.682 g/mol (C₂₉H₄₅R₂N₃O₁₈, R = next and previous repeats, not counted in mol weight)