Effect of white rot basidiomycetes on chemical composition and in vitro digestibility of oat straw and alfalfa stems.

Five white rot basidiomycetes were evaluated for their potential to improve ruminal degradation of oat straw and alfalfa stems. Phanerochaete chrysosporium (PC), Scytinostroma galactinum (SG), Phlebia tremellosa (PT), Phellinus pini (PP), and Pholiota mutabilis (PM) were incubated on oat straw and alfalfa stems for 30 d at 28 degrees C and 90% relative humidity. Detergent fiber and total fiber components (neutral sugars, uronic acids, Klason lignin [KL], and ester- and ether-linked non-core lignin phenolics), core lignin nitrobenzene oxidation products, and IVDMD were determined. Electron microscopy of KMnO4-stained and cellulase/colloidal gold-labeled sections was used to monitor fungal activity. Large losses of DM were noted for all fungal species on both substrates. Lignin (KL and ADL) was removed (P less than .05) from oat straw by PC and PT treatment, but no net loss of lignin was observed for fungal treatment of alfalfa stems. Cell-wall polysaccharides were removed from both substrates by fungal activity. Only PC increased (P less than .05) IVDMD of oat straw, and SG, PT, PP, and PC treatment decreased (P less than .05) IVDMD of alfalfa stems, presumably because the fungi removed the most readily fermentable polysaccharides. Transmission electron microscopy using KMnO4 staining showed a nonselective white rot attack. Cytochemical studies using colloidal gold-labeled exo- and endocellulases were used to map the location of cellulose in the cell wall before and after decay by the white rot fungi. All the white rot fungi tested had eroded and thinned cell walls. Residual cell walls were well-labeled; both endo- and exocellulose-colloidal gold identified the cellulosic wall material that remained.(ABSTRACT TRUNCATED AT 250 WORDS)