Physicochemical and ultrastructural changes in fungal treated switchgrass and their impact on enzymatic digestibility

Solid-state fermentation of switchgrass using white-rot basidiomycete fungi including wild-type Trametes versicolor strain 52J (Tv 52J), a cellobiose dehydrogenase-deficient strain (mutant) T. versicolor strain m4D (Tv m4D), and wild-type Phanerochaete chrysosporium (PC) was conducted at a temperature of 34 °C, time of 28 d, hammer mill screen size of 6.4 mm and inoculum volume of 10 mL. Pretreatment with PC resulted in a significant cellulose loss (13.5 %) and slightly higher delignification compared to the other fungal strains. XRD analysis showed that fungal pretreatment increased the crystallinity index of switchgrass with PC-treated sample having 5.6 % more than untreated sample. Pretreatment resulted in approximately 5-fold and 7.7-fold increase in surface area and volume of pores, respectively, in Tvm4D-treated samples as compared to the control. SEM and TEM images revealed a significant change in cell wall morphology upon pretreatment with all three fungal strains. Fungal pretreatment of switchgrass enhanced the output of enzymatic hydrolysis.