Ability of a prairie cordgrass hydrolysate to support fungal pullulan production relative to nitrogen source addition

The water soluble polysaccharide gum pullulan is a commercially available biopolymer that has industrial applications. The carbon source glucose is known to support fungal pullulan production. Plant biomass contains cellulose which can be degraded to glucose by enzymatic treatment. A possible source of plant biomass are grasses which can be produced in high yield plus contain a high content of cellulose. Most prairie grasses, such as prairie cordgrass, are used for livestock grazing or harvested as hay. In this study, the ability of the pullulan-producing fungus Aureobasidium pullulans ATCC 42023 to utilize a prairie cordgrass hydrolysate to synthesize pullulan was investigated relative to nitrogen source addition. A hydrolysate of prairie cordgrass was prepared by autoclaving the ground, dried grass in a phosphate buffer (pH 5.0) and then hydrolyzing the suspension at 40^oC with a combination of cellulase and cellobiase for 48 hours. The filtrate was collected and used in the pullulan medium. The phosphate-buffered medium (pH 6.0) either contained ammonium sulfate as the nitrogen source or no nitrogen source was added. The fungal cells were grown in the hydrolysate-containing medium in shake flask cultures for 168 hours at 30^oC. The concentration of pullulan produced was measured gravimetrically. It was determined that ATCC 42023 synthesized the highest pullulan level after 168 hours of growth on the medium containing no ammonium sulfate. In summary, it was found that the ability of the fungus A. pullulans ATCC 42023 to produce pullulan on the prairie cordgrass hydrolysate was diminished by nitrogen source addition.