Production of cellulases and xylanases by white-rot fungi cultured in corn stover media for ruminant feed applications

Growth rate and fungal aggressiveness were measured in Phanerochaete chrysosporium, Sporotrichum pulverulentum, Bjerkandera adusta, Pleurotus ostreatus, Trametes zonatus, and Trametes trogii in solid culture media with corn stover hybrid (subtropical and High Valleys germplasm). Endoglucanase, exoglucanase, β-glucosidase, and xylanase activities were assayed at 39 °C, pH 6.0 in liquid culture media with H324, AS822 and AS951, reflecting the average temperature and pH in ruminants. The enzyme activities in enzyme extracts of B. adusta and T. trogii in culture medium with neutral detergent fiber, acid detergent fiber, and acid detergent lignin fractions were also analyzed. H324, AS822, and AS951 tended to have more neutral detergent fiber than other corn stover hybrids: AS951 had more cellulose, AS822 more hemicellulose, and H324 more acidic detergent lignins. Although P. chrysosporium and S. pulverulentum had the highest growth rate in AS822, H324, and G766 culture medium, B. adusta and T. trogii were more aggressive. Growth rate was not clearly related to fungal adaptation or enzyme activity. B. adusta enzyme extracts showed the highest endoglucanase activity, T. trogii the highest xylanase activity, and S. pulverulentum the highest β-glucosidase activity. Increasing the lignin proportion in the culture medium (H324 and ADL) improved endoglucanase and xylanase peaks and the endoglucanase:xylanase ratio. Culture medium composition and fungus could promote useful enzyme activity proportions for corn stover fiber degradation.