First report of a lyase for cepacian, the polysaccharide produced by Burkholderia cepacia complex bacteria

Abstract

Bacteria belonging to the Burkholderia cepacia complex (Bcc) are interesting for their involvement in pulmonary infections in patients affected by cystic fibrosis (CF) or chronic granulomatous disease. Many Bcc strains isolated from CF patients produce high amounts of exopolysaccharides (EPS). Although different strains sometimes biosynthesise different EPS, the majority of Bcc bacteria produce only one type of polysaccharide, which is called cepacian. The polymer has a unique heptasaccharidic repeating unit, containing three side chains, and up to three O-acetyl substituents.. We here report for the first time the isolation and characterisation of a lyase active towards cepacian produced by a Bacillus sp., which was isolated in our laboratory. The enzyme molecular mass, evaluated by size-exclusion chromatography, is 32,700 ± 1500 Da. The enzyme catalyses a β-elimination reaction of the disaccharide side chain β- d-Gal p-(1 → 2)-α- d-Rha p-(1→ from the C-4 of the glucuronic acid residue present in the polymer backbone. Although active on both native and de-acetylated cepacian, the enzyme showed higher activity on the latter polymer.