Dr. Mark Wilkins, former Professor at Biosystems and Agricultural Engineering (BAE), Oklahoma State University (OSU), collaborated with two other OSU faculty Drs. Michael Buser (BAE) and Stephen Marek (Entomology and Plant Pathology), and Dr. Julie Carrier from Biosystems Engineering and Soil Science at University of Tennessee to investigate whether oyster mushrooms, Pleurotus ostreatus, could be used to break down lignin in switchgrass in a controlled storage environment. The research team aimed to develop and optimize an integrated switchgrass storage fungal pretreatment system, which could aid in lignin degradation and reduce the severity of subsequent thermochemical pretreatment processes, which are necessary for preparing switchgrass from enzymatic hydrolysis.
Small square bales of “Kanlow” switchgrass were used to test the effect of fungal application on lignin degradation and sugar content during storage. Three different rates of oyster mushroom spores were applied to the switchgrass bales prior to storage in a moisture and temperature controlled laboratory. Degradation of lignin, cellulose and hemicellulose was monitored every 27 days during storage of bales with and without fungus applied.
Wilkins’ group found that the use of fungus promoted lignin degradation compared to controls in bales stored at 50% and 75% moisture content. However, significant degradation of cellulose occurred if switchgrass was stored with fungus for more than 55 to 60 days. “In order to preserve cellulose, fungal pretreatment should not continue beyond 60 days. The timing of storage is important since storing bales for more than two months resulted in significant loss of cellulose, which is the most valuable portion of the grass,” Wilkins said. “In small bales, degradation of lignin, cellulose, and hemicellulose occurred in control bales due to microorganisms already present in the bales, but degradation of lignin and hemicellulose was less than that observed in bales to which fungus was applied,” Wilkins added.
Wilkins’ group also added copper, manganese and glucose to switchgrass along with the fungus to determine if these supplements would improve lignin degradation by P. ostreatus as other literatures suggested that these supplements would boost lignin degrading enzyme activity.
“All of the supplements added decreased lignin degradation compared to no supplementation. This result indicates that all of the nutrients needed for fungal growth are present in switchgrass, and costly supplementation is not required”, Wilkins said.
Funding of this project was provided by the U.S. Department of Agriculture-National Institute of Food and Agriculture (USDA-NIFA) through the South Central Sun Grant Program.