Biological and physical properties of an extracellular polysaccharide from Pseudomonas phaseolicola

Abstract

A purified extracellular polysaccharide (EPS) from Pseudomonas phaseolicola was tested on 15 genetically different bean cultivars. Persistent water-soaking was only induced in bean leaves of disease-susceptible cultivars but not in disease-resistant cultivars or other plant species. The EPS was homogeneous after ultracentrifugation with a sedimentation coefficient of S 20. urea 90. By comparison with other polysaccharides, a molecular weight of 6·5 × 10 6 daltons was estimated. Electron microscopy and negative staining revealed homogeneous spherical- to disc-shaped particles with a mean diameter of 190 Å. The EPS aggregated readily in water and disaggregated in 4 M urea. No specific absorbance in u.v. light between 200 and 320 nm could be detected. The EPS did not migrate during electrophoresis or t.l.c. EPS preparations from three different bacterial cultures and an EPS preparation from infected bean leaves showed one precipitin line with P. phaseolicola -antiserum whereas EPS from Xanthomonas translucens f. sp. cerealis and P. fluorescens did not show any precipitin line with P. phaseolicola -antiserum.