Comparison of extracellular polysaccharide of Xanthomonas campestris from culture and from infected cabbage leaves

The extracellular polysaccharide fraction of Xanthomonas campestris was precipitated with hexadecyltrimethylammonium bromide from aqueous extracts of cabbage leaves infected with the black rot pathogen, and further purified by repeated precipitation with ethanol. The polysaccharide fraction was shown to be similar to extracellular polysaccharide fraction purified from culture fitlrates of X. campestris. Sugars present in samples of acid-hydrolyzed polysaccharide were identified by gas–liquid chromatography. Chromatograms showed that polysaccharide purified from infected cabbage leaves contained glucose, mannose, and glucuronolactone in ratios similar to those of the polysaccharide from culture filtrates. Polysaccharide purified from noninfected cabbage leaves contained only glucose and galactose. The polysaccharide from infected cabbage leaves was serologically related to polysaccharide from culture filtrates. In immunodiffusion tests both the polysaccharide fractions from culture filtrates and that from infected leaves reacted to give two precipitin bands with an antiserum to the polysaccharide from culture filtrates. No precipitin bands formed with polysaccharide from noninfected leaves. Antibodies against the culture polysaccharide were completely removed from the antiserum by the polysaccharides isolated from infected cabbage leaves. A weakly virulent isolate of X. campestris did not produce extracellular polysaccharide in culture filtrates.