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

Pullulan is an extracellular polysaccharide biopolymer synthesized by the fungus Aureobasidium pullulans. The commercial application of this gum involves it being used in the production of water-soluble films. With the plant prairie cordgrass containing about 30% cellulose, dilute acid hydrolysis of its cellulose releases glucose which can support fungal pullulan production. In this investigation, a previously isolated deoxyglucose-resistant mutant of A. pullulans was compared to its parent strain ATCC 42023 relative to their ability to elaborate pullulan on the dilute acid-hydrolyzed cordgrass. The prairie cordgrass was treated with 0.225% sulfuric acid in an autoclave for 30 minutes at 121^oC under a pressure of 17 pounds/square inch. After the hydrolysate was filtered, 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 followed for 168 hours at 30^oC. Pullulan levels were measured gravimetrically following ethanol precipitation of the polysaccharide from the medium. The highest pullulan concentration was produced by the mutant strain grown on the 0.225% sulfuric acid hydrolysate-containing medium after 168 h of growth. The mutant synthesized a 1.5-fold higher pullulan level than the polysaccharide 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 higher level of pullulan production compared to its parent strain when both were grown on a dilute acid-treated prairie cordgrass hydrolysate.