Comparative studies of lipopolysaccharide and exopolysaccharide from a virulent strain of Pseudomonas solanacearum and from three avirulent mutants

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Abstract
The composition of the P. solanacearum lipolysaccharide (LPS) was found to be similar to that described for the LPS of enterobacteria. The lipid A contained fatty acids and glucosamine in a molar ratio of 5:2. The LPS fraction contained 2-keto-3-deoxyoctulosonic acid, L-glycero-D-mannoheptose, hexoses (glucose, rhamnose and glucosamine) and a pentose (xylose). The LPS from the wild-type strain (GMI1000), from the spontaneous rough mutant (GMI2000) and from their respective acridine orange-resistant (Acrr) mutants (GMI1178 and GMI2179) contained the same component sugars in their polysaccharide moieties, but the relative amounts of each sugar varied greatly. Spontaneous mutation to the rough type was characterized by a decrease in the ratio of rhamnose to glucose, whereas a reverse effect was seen for the acridine orange resistance mutation from the parent strains (GMI1000 and GMI2000) to the respective mutant strains (GMI1178 and GMI2179). The exopolysaccharide (EPS) from GMI1000 was found to be composed of 2 fractions: a heteropolysaccharide (galactosamine, glucose and rhamnose) excluded from Sephadex G-50 and an additional glucan with a lower MW. Strains GMI1000 and GMI1178 produced comparable amounts of EPS, GMI2179 synthesized less EPS, and GMI2000 produced no detectable EPS. High-pressure liquid chromatography and 13C NMR analyses revealed some differences between these EPS. The glucan fraction seemed to be the major component of the EPS from GMI2179, whereas GMI1000 and GMI1178 EPS contained both fractions and appeared to differ in the structures of their heteropolysaccharide fractions. Viscosity measurements confirmed differences between whole EPS produced by the 3 strains.