Pullulans produced by strains of Cryphonectria parasitica—I. Production and characterisation of the exopolysaccharides

Studies published during the last four decades indicated that pullulan has mainly α-(1→6) maltotriose subunits, accompanied by α-(1→6) maltotetraose subunits and other anomalies in the polymer chain. The presence and the extent of these anomalies depend on the strain of Aureobasidium pullulans used for obtaining the pullulan as exocellular material, and on the culture conditions as well. Besides A. pullulan, other fungi produce this polysaccharide. In all cases, the maximum amount of α-(1→6) maltotetraose subunits was believed to be 7%. This paper reports the characterization of pullulan samples, obtained by liquid cultures of a virulent strain (CP159) and two hypovirulent strains (CP263 and CP102) of Cryphonectria parasitica. It was found that in all cases pullulan was much richer in α-(1→6) maltotetraose subunits than the pullulan(s) so far investigated. Chestnut blight caused by C. parasitica is a disease of worldwide importance in chestnut production. The structure of pullulan could be correlated with the pathogenesis and symptoms expressed by infected plants.