Stenotrophomonas maltophilia is a non-fermenting Gram-negative microorganism capable of causing chronic pulmonary infection in cystic fibrosis patients and its ability to form biofilms on polystyrene and glass surfaces, as well as on cystic fibrosis-derived bronchial epithelial IB3-I cells was recently demonstrated. The latter evidence might explain the power of S. maltophilia to produce persistent lung infections, despite intensive antibiotic treatment. In addition to being important components of the extracellular biofilm matrix, polysaccharides are involved in virulence, as they contribute to bacterial survival in a hostile environment. With the aim of contributing to the elucidation of S. maltophilia virulence factors, the exopolysaccharides produced by two mucoid clinical isolates of S. maltophilia obtained from two cystic fibrosis patients were completely characterised, mainly by means of ESI-MS and NMR spectroscopy. The results showed that, although the two isolates were recovered from two different patients living in different countries (Italy and France), the exopolysaccharides produced have an identical primary structure, with the following repeating unit: The exopolysaccharide is highly negatively charged for the presence of three uronic acids on four residues in the repeating unit. Moreover, an ether-linked d-lactate substituent is located on C-3 and one O-acetyl group on C-4 of the galacturonic acid side chain. Another O-acetyl group substitutes C-2 of the galacturonic acid in the backbone, making this primary structure unique.

NMR, exopolysaccharide, Stenotrophomonas maltophilia, ESI-MS, cystic fibrosis, primary structure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,4	bDGlcp	103.35	74.48	75.30	80.36	75.36	61.47
4,3,3	lRLac	182.12	76.60	19.63
4,3	bDGalpA	104.33	70.57	81.25	68.34	76.37	175.32
4	bDGalpA	103.39	71.24	81.69	78.94	75.96	174.50
	bDGlcpA	103.39	73.65	75.30	81.86	76.23	175.42


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,4	bDGlcp	4.90	3.33	3.68	3.55	3.55	3.72-3.92
4,3,3	lRLac	-	4.15	1.40
4,3	bDGalpA	4.68	3.68	3.53	4.35	4.00	-
4	bDGalpA	4.50	3.83	4.00	4.68	4.05	-
	bDGlcpA	4.50	3.41	3.68	3.75	3.89	-


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,4	bDGlcp	103.35/4.90	74.48/3.33	75.30/3.68	80.36/3.55	75.36/3.55	61.47/3.72-3.92
4,3,3	lRLac		76.60/4.15	19.63/1.40
4,3	bDGalpA	104.33/4.68	70.57/3.68	81.25/3.53	68.34/4.35	76.37/4.00	
4	bDGalpA	103.39/4.50	71.24/3.83	81.69/4.00	78.94/4.68	75.96/4.05	
	bDGlcpA	103.39/4.50	73.65/3.41	75.30/3.68	81.86/3.75	76.23/3.89	

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

762.576 g/mol (C₂₇H₃₈R₂O₂₅, R = next and previous repeats, not counted in mol weight)