Chemical analysis of alginates from mucoid strains of Pseudomonas aeruginosa

Mucoid or alginate-producing strains of Pseudomonas aeruginosa are the major pathogens in chronic pulmonary infections in patients with cystic fibrosis (CF), in which alginate is considered a major virulence factor. Bacterial alginates are linear exopolysaccharides comprising (1 +4)-linked p-D-mannuronate (M) and its C5-epimer a-L-guluronate (G), in which mannuronate residues may be either monoor di-0-acetylated [l] . Alginate biosynthetic regulation is complex and involves environmentally responsive signal transduction systems, histone-like elements [2] and the possible metabolic regulation of key enzymic activities [3]. Expression of the mucoid phenotype involves three chromosomal loci: biosynthetic genes are located at 341nin on the P. aeruginosu genome, regulatory genes at 91Nn. and the controlling rnuc or master switch region at 70min [4]. Laboratory-derived strains containing rnuc mutations allowed the isolation of stable mucoid variants [5] that were designated PA0568 (rnuc2). PA0578 (muc22) and PA0579 (muc23) respectively. These exhibit differing medium-dependent expression of the mucoid phenotype when grown in virro on various agar-based media [5,6]. This medium-dependent expression of mucoidy is also exhibited by a variety of wildtype CF isolates and therefore facilitates their classification into "muc-like" groups. In this study 'H-nmr has been used to compare the structural composition of alginates produced both by rnuc strains and CF isolates. Experimental procedures have been described previously