Fungal polysaccharide production from a xylose-containing prairie cordgrass hydrolysate

The biopolymer pullulan is a commercially available, water soluble polysaccharide gum that has several industrial applications. Various carbon sources can support fungal pullulan production including xylose. It was of interest to learn how effectively pullulan could be produced from the xylose present in a plant biomass hydrolysate. Prairie grasses represent a potential source of plant biomass. These grasses produce a high yield and contain a relatively high hemicellulose level. Currently, prairie grasses, including prairie cordgrass, are used for grazing by livestock 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. A hydrolysate of prairie cordgrass was prepared by autoclaving the dried grass in a phosphate buffer (pH 5.0). The solids were subsequently hydrolyzed at 40^oC with a combination of cellulase and cellobiase for 48 hours. After the solids were collected and dried, they were treated with xylanase (pH 6.0) for 48 hours at 50^oC. The filtrate was collected and used in the pullulan medium.  The fungal cells were grown in a phosphate-buffered medium (pH 6.0) containing prairie cordgrass hydrolysate in shake flask cultures.  The strain was grown 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. In conclusion, it was found that the fungus A. pullulans ATCC 42023 could utilize a xylose-containing prairie cordgrass hydrolysate to produce pullulan.