Bacterial extracellular polysaccharides are known as a cell-bound capsule, a sheath, or a slime, which is excreted into the environment. They play an important role in virulence of medical bacteria and plant-to-symbiont interaction and are used for serotyping of bacteria and production of vaccines. Some exopolysaccharides have commercial applications in industry, and claims of health benefits have been documented for an increasing number of them. Exopolysaccharides have diverse composition and structure, and some contain sugar and non-sugar components that are found in bacterial carbohydrates only. The present article provides an updated collection of the data on exopolysaccharides of various classes of gram-negative and gram-positive bacteria reported until the end of 2019. When known, biosynthesis pathways of exopolysaccharides are treated in a summary manner. References are made to structure and biosynthesis relatedness between exopolysaccharides of different bacterial taxa as well as between bacterial polysaccharides and mammalian glycosaminoglycans.

polysaccharide structure, Gram-negative bacteria, capsule, Biofilm, polysaccharide biosynthesis, gram-positive bacteria, Monosaccharide composition, Bacterial exopolysaccharide, non-sugar component

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

834.727 g/mol (C₃₂H₅₀R₂O₂₅, R = next and previous repeats, not counted in mol weight)

Burkholderia species are a vast group of human pathogenic, phytopathogenic, and plant- or environment-associated bacteria. B. pseudomallei, B. mallei, and B. cepacia complex are the causative agents of melioidosis, glanders, and cystic fibrosis-related infections, respectively, which are fatal diseases in humans and animals. Due to their high resistance to antibiotics, high mortality rates, and increased infectivity via the respiratory tract, B. pseudomallei and B. mallei have been listed as potential bioterrorism agents by the Centers for Disease Control and Prevention. Burkholderia species are able to produce a large network of surface-exposed polysaccharides, i.e., lipopolysaccharides, capsular polysaccharides, and exopolysaccharides, which are virulence factors, immunomodulators, major biofilm components, and protective antigens, and have crucial implications in the pathogenicity of Burkholderia-associated diseases. This review provides a comprehensive and up-to-date account regarding the structural elucidation and biological activities of surface polysaccharides produced by Burkholderia species. The chemical synthesis of oligosaccharides mimicking Burkholderia polysaccharides is described in detail. Emphasis is placed on the recent research efforts toward the development of glycoconjugate vaccines against melioidosis and glanders based on synthetic or native Burkholderia oligo/polysaccharides.

lipopolysaccharides, Burkholderia, capsular polysaccharides, Oligosaccharides, glycoconjugate vaccines, antigens, exopolysaccharides, surface polysaccharide, virulence factor, Biofilm, chemical synthesis, bioterrorism

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

834.727 g/mol (C₃₂H₅₀R₂O₂₅, R = next and previous repeats, not counted in mol weight)

An acidic exopolysaccharide (EPS) produced by the diazotrophic bacterium Burkholderia tropica, strain Ppe8, was isolated from the culture supernatant of bacteria grown in a synthetic liquid medium containing mannitol and glutamate. Monosaccharide composition showed Rha, Glc and GlcA in a 2.0:2.0:1.0 molar ratio, respectively. Further structural characterization was performed by a combination of NMR, mass spectrometry and chemical methods. Partial acid hydrolysis of EPS provided a mixture of acidic oligosaccharides that were characterized by ESI-MS, giving rise to ions with m/z 193 (GlcA-H)-, 339 (GlcA,Rha-H)-, 501 (GlcA,Rha,Glc-H)-, 647 (GlcA,Rha2,Glc,-H)-, 809 (GlcA,Rha2,Glc2,-H)- and 851 (GlcA,Rha2,Glc2,OAc-H)-. Carboxyreduced EPS (EPS-CR) had Glc and Rha in a 3:2 ratio, present as d- and l-enantiomers, respectively. Methylation and NMR analysis of EPS and EPS-CR showed a main chain containing 2,4-di-O-Rhap, 3-O-Rhap and 4-O-Glcp. A GlcA side chain unit was found in the acidic EPS, substituting O-4 of α-l-Rhap units. This was observed as a non-reducing end unit of glucopyranose in the EPS-CR. Acetyl esters occured at O-2 of β-l-Rhap units. From the combined results herein, we determined the structure of the exocellular polysaccharide produced by B. tropica, Ppe8, as being a pentasaccharide repeating unit as shown.

exopolysaccharide, EPS, Burkholderia tropica, diazotrophic, endophytic

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,2	bDGlcp	103.0	73.8	75.5	78.3	?	60.9
3,4,4	aDGlcpA	94.6	75.6	74.2	76.6	73.1	175.5
3,4	aLRhap	97.9	74.0	74.5	78.1	72.3	16.7
3	aDGlcp	97.9	72.1	71.8	79.5	72.9	60.7
2	Ac	173.4	20.3
	bLRhap	99.0	68.1	81.1	?	70.8	16.7


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,2	bDGlcp	4.62	3.28	3.41	3.62	3.45	3.71
3,4,4	aDGlcpA	5.02	3.55	3.77	3.63	3.69	-
3,4	aLRhap	4.88	4.18	3.58	3.99	3.88	4.07
3	aDGlcp	4.96	3.74	3.5	3.54	3.55	3.76
2	Ac	-	2.15
	bLRhap	5.02	5.59	4.16	3.87	3.49	1.32


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,2	bDGlcp	103.0/4.62	73.8/3.28	75.5/3.41	78.3/3.62	?/3.45	60.9/3.71
3,4,4	aDGlcpA	94.6/5.02	75.6/3.55	74.2/3.77	76.6/3.63	73.1/3.69	
3,4	aLRhap	97.9/4.88	74.0/4.18	74.5/3.58	78.1/3.99	72.3/3.88	16.7/4.07
3	aDGlcp	97.9/4.96	72.1/3.74	71.8/3.5	79.5/3.54	72.9/3.55	60.7/3.76
2	Ac		20.3/2.15
	bLRhap	99.0/5.02	68.1/5.59	81.1/4.16	?/3.87	70.8/3.49	16.7/1.32

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

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

834.727 g/mol (C₃₂H₅₀R₂O₂₅, R = next and previous repeats, not counted in mol weight)