Macromolecular properties of cepacian in water and in dimethylsulfoxide.

Cepacian is the exopolysaccharide produced by the majority of the so far investigated clinical strains of the Burkholderia cepacia complex. This is a group of nine closely related bacterial species that might cause serious lung infections in cystic fibrosis patients, in some cases leading to death. In this paper the aggregation ability and the conformational properties of cepacian chain were investigated to understand its role in biofilm formation. Viscosity and atomic force microscopy studies in water and in mixed (dimethylsulfoxide/water) solvent indicated the formation of double stranded molecular structures in aqueous solutions. Inter-residue short distances along cepacian chain were investigated by NOE NMR, which showed that two side chains of cepacian were not conformationally free due to strong interactions with the polymer backbone. These interactions were attributed to hydrogen bonding and contributed to structure rigidity.

Exopolysaccharides produced by clinical strains belonging to the Burkholderia cepacia complex.

BACKGROUND: In the frame of a research line dedicated to better clarify the role of exopolysaccharides (EPS) in bacterial virulence, EPS produced by species of the Burkholderia cepacia complex (Bcc), namely Burkholderia multivorans, Burkholderia cenocepacia, and a Bcc member of undetermined genomovar, all isolated at the Cystic Fibrosis Regional Centre of Florence (Italy), were investigated for they structural properties. METHODS: Three strains of B. multivorans, three of B. cenocepacia and one of a Bcc member of undetermined genomovar were isolated from CF patients. The reference strains C1576 and J2315, for genomovar II and III, respectively, were included in the study. The bacteria were grown on solid media, the exopolysaccharides produced were purified, and their structures were determined. In addition, sugar analysis of sputum samples was accomplished to search for EPS produced in vivo. RESULTS: Six strains out of seven produced the exopolysaccharide cepacian, while one strain of B. multivorans produced a completely different polymer, previously known in the literature as PS1. Two strains synthesised very small amounts of EPS. No definitive evidence for the presence of cepacian in sputum samples was found. CONCLUSIONS: Most strains examined produced abundant amounts of polysaccharides. Cepacian was the most common EPS isolated and its production was not associated to a particular genomovar.

Exopolysaccharides produced by Burkholderia cenocepacia recA lineages IIIA and IIIB.

Clinical and environmental strains of Burkholderia cenocepacia belonging to the recA lineages IIIA and IIIB were examined for exopolysaccharide (EPS) production. The exopolysaccharides structure was determined using mainly gas chromatography coupled to mass spectrometry and NMR spectroscopy. All the strains produced Cepacian, a highly branched polysaccharide constituted of a heptasaccharide repeating unit, composed of one rhamnose, one glucose, one glucuronic acid, one mannose and three galactose residues. This polymer is the most common exopolysaccharide produced by strains of the Burkholderia cepacia (Bcc) complex. One clinical strain produced also another polysaccharide constituted of three galactose units and one 3-deoxy-D-manno-2-octulosonic acid residues, a polymer that was previously isolated from two strains of B. cepacia genomovar I and B. cenocepacia IIIA.

Enantiomerization of 3-carbethoxy-l,4-benzodiazepin-2-one: combined chiral HPLC and spectroscopic study.

Recently developed chiral HPLC columns CHIRIS AD1 and CHIRIS AD2 have been demonstrated to separate racemic, configurationally unstable ethyl-7-chloro-2-oxo-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine-3-carboxylate (1) and its 3-methyl congener 2; fast on-column enantiomerization of configurationally unstable 1 was observed, however. Addition of 0.1% of AcOH to the eluting mixture inhibits enantiomerization, whereas the same percentage of Et(3)N completely precludes enantioseparation, suggesting base-catalysis by free beta-aminoethyl groups, present in low percentage in chiral stationary phase (CSP). When both CSPs were prepared under conditions of nonexhaustive acylation by N-DNB-alpha-aminoacids, no separation of 1 was observed. The rate of enantiomerization on CHIRIS AD2 was determined at 25 degrees C, the mechanism is discussed, and experimental results correlated with calculated relative stabilities of the tautomers la-c. Absolute (3S) configuration of (+) enantiomers of 1 and 2 was determined by comparison of their eluation profile to that of (+/-)-3 and (3S)-(+)-3, taking into account relative (psia or psie) configuration of the prevailing conformer in solution.