ALTERATIONS IN STRUCTURE, CHEMISTRY, AND BIODEGRADABILITY OF GRASS LIGNOCELLULOSE TREATED WITH THE WHITE-ROT FUNGI CERIPORIOPSIS-SUBVERMISPORA AND CYATHUS-STERCOREUS

The white rot fungi Ceriporiopsis subvermispora FP-90031-sp and Cyathu s stercoreus ATCC 36910 were evaluated for their ability to delignify Bermuda grass (Cynodon dactylon) stems and improve biodegradability. C ompositional and structural alterations in plant cell walls effected b y the fungi were determined by nuclear magnetic resonance spectroscopy , gas chromatography of alkali-treated residues, microspectrophotometr y, and electron microscopy. Contaminating bacteria and fungi, which gr ew from unsterilized Bermuda grass stems, did not alter the improvemen t in grass biodegradability by either of the fungi from that of gas-st erilized stems. The biodegradation of stems by ruminal microorganisms, after treatment for 6 weeks with C. subvermispora or C. stercoreus, w as improved by 29 to 32% and by 63 to 77%, respectively; dry weight lo sses caused by pretreatment with the fungi were about 20% over that in untreated, control stems. Both fungi preferentially removed aromatics to carbohydrates, and C. subvermispora removed proportionately more g uaiacyl units than did C. stercoreus. Substantial amounts of ester-lin ked p-coumaric and ferulic acids were removed by both fungi, and about 23 and 41% of total aromatics (determined after 4 M NaOH direct treat ment) were removed from the plant biomass after incubation with C. sub vermispora and C. stercoreus, respectively. UV absorption microspectro photometry indicated that ester-linked phenolic acids were totally rem oved from the parenchyma cell walls, and these cells were readily and completely degraded by both fungi. However, aromatic constituents were only partially removed from the more recalcitrant sclerenchyma cell w alls, resulting in variation in electron density and random digestion pits after incubation with fiber-degrading bacteria. These fungi varie d in their potential to delignify various types of plant cell walls.