Production of pullulan on a dilute acid-treated prairie cordgrass hydrolysate by a fungal mutant strain relative to its parent strain

Pullulan is a polysaccharide gum synthesized extracellularly by the fungus Aureobasidium pullulans. An important commercial application of this gum involves its being used for the production of water-soluble films. Considering that the plant prairie cordgrass contains about 30% cellulose, treatment of its cellulose with dilute acid promotes degradation to glucose which is a substrate for fungal pullulan production. In this study, pullulan production by a previously isolated deoxyglucose-resistant mutant of A. pullulans was compared to production by its parent strain ATCC 42023 on the dilute acid-hydrolyzed cordgrass. The prairie cordgrass was treated with 0.275% sulfuric acid in an autoclave for 30 minutes at 121^oC under a pressure of 17 pounds/square inch. After filtering the hydrolysate, the filtrate was utilized in a 0.5% phosphate buffered medium (pH 6.0) containing 0.1% yeast extract, 0.1% sodium chloride and 0.02% magnesium sulfate. Pullulan production by the strains grown on the acid hydrolysate-containing medium was monitored for 168 hours at 30^oC. The level of pullulan was measured gravimetrically following ethanol precipitation of the polysaccharide from the medium. The highest pullulan concentration was produced by the mutant or parent strain grown on the 0.275% sulfuric acid hydrolysate-containing medium after 168 hours. The mutant strain synthesized a slightly higher pullulan level than the level produced by ATCC 42023 after 168 hours of growth on the dilute acid hydrolysate-containing medium. In summary, a deoxyglucose-resistant fungal mutant supported a slightly higher level of pullulan production compared to its parent strain on a medium containing dilute acid-treated prairie cordgrass hydrolysate.