MICROBIAL DELIGNIFICATION WITH WHITE-ROT FUNGI IMPROVES FORAGE DIGESTIBILITY

Three wild-type white rot fungi and two cellulase-less mutants develop ed from Phanerochaete chrysosporium K-3 (formerly Sporotrichum pulveru lentum) were tested for their ability to delignify grass cell walls an d improve biodegradation by rumen microorganisms. Fungal-treated and c ontrol stems of Bermuda grass were analyzed for their content of ester - and ether-linked aromatics by using alkali extraction and gas chroma tography, for in vitro dry weight digestion and production of volatile fatty acids in in vitro fermentations with mixed ruminal microorganis ms, for loss of lignin and other aromatics from specific cell wall typ es by using microspectrophotometry, and for structural changes before and after in vitro degradation by rumen microorganisms by using transm ission electron microscopy. P. chrysosporium K-3 and Ceriporiopsis sub vermispora FP 90031-sp produced the greatest losses in lignin and impr oved the biodegradation of Bermuda grass over that of untreated contro l substrate. However, C. subvermispora removed the most lignin and sig nificantly improved biodegradation over all other treatments. Phellinu s pini RAB-83-19 and cellulase-less mutants 3113 and 85118 developed f rom P. chrysosporium K-3 did not improve the biodegradation of Bermuda grass lignocellulose. Results indicated that C. subvermispora extensi vely removed ester-linked p-coumaric and ferulic acids and also remove d the greatest amount of non-ester-linked aromatics from plant cell wa lls. Microscopic observations further indicated that C. subvermispora removed esters from parenchyma cell walls as well as esters and lignin from the more recalcitrant cell walls (i.e., sclerenchyma and vascula r tissues). C. subvermispora improved in vitro digestion and volatile fatty acid production by ruminal microorganisms by about 80%, while dr y matter loss due to fungi was about 20% greater than loss in untreate d control stems. The chemical and structural studies used identified s ites of specific fungal attack and suggested mechanisms whereby improv ement occurred.