Origin of the Polysaccharide Component of Ooze from Plants Infected with Erwinia amylovora

SUMMARY: The composition of extracellular polysaccharides produced by Erwinia amylovora in defined culture media was compared with that of the polysaccharide present in the ooze produced during fireblight infection. The results strongly suggested that the ooze polysaccharide was of bacterial origin.

Two distinct polysaccharides were produced in vitro. One contained galactose (61 to 69%), glucose (8 to 11%), mannose (2 to 6%) and uronic acid (16 to 23%) and the other contained only fructose. Both the quantity and composition of the polysaccharide produced was determined by the nature and concentration of the sugar or sugar alcohol supplied and by the nature of the nitrogen source.

Evidence is also presented which suggests that production of the ooze-like polysaccharide is a virulence determinant and that this polysaccharide is similar in composition to the capsule. Preliminary studies indicate the presence of capsule and polysaccharide-hydrolysing enzymes in lysates of phage-infected bacteria.