Pullulan production by Aureobasidium pullulans grown on a cordgrass hydrolysate containing primarily xylose

The polysaccharide pullulan is a fungal gum that has industrial uses. It has been shown that xylose can support pullulan production by the fungus Aureobasidium pullulans. Although pullulan can be synthesized by the fungus utilizing xylose as a carbon source, it was not clear how effectively the polysaccharide could be produced from the xylose and other sugars present in a plant biomass hydrolysate. A possible source of plant biomass is the high yielding prairie cordgrass. The ability of A. pullulans ATCC 42023 to synthesize pullulan from a prairie cordgrass hydrolysate was studied here. The cordgrass hydrolysate was initially prepared by autoclaving the dried grass in a phosphate buffer (pH 5.0). Next, the solids were hydrolyzed at 40^oC with a combination of cellulase and cellobiase for 48 hours. Treatment of the dried solids with xylanase (pH 6.0) for 48 hours at 50^oC was performed. The filtered suspension was used in the pullulan medium.  The cells were grown for 168 hours at 30^oC in shake flask cultures of a phosphate-buffered medium (pH 6.0) containing prairie cordgrass hydrolysate. The pullulan concentration was determined gravimetrically. After 168 hours, ATCC 42023 cells synthesized the highest pullulan level on the medium. The pullulan concentration produced by ATCC 42023 on the hydrolysate was slightly higher than if the strain was grown on the same concentrations of xylose, glucose and arabinose present in the hydrolysate. Overall, it was concluded that the fungus A. pullulans ATCC 42023 could utilize a cordgrass hydrolysate to effectively produce pullulan.