Platt, M.W., Department of Plant Pathology and Microbiology, Hebrew University, Israel
Hadar, Y., Department of Plant Pathology and Microbiology, Hebrew University, Israel
Hisdai, A., Department of Plant Pathology and Microbiology, Hebrew University, Israel, Department of Animal Metabolism, Volcani Institute, Israel
Chet, I., Department of Plant Pathology and Microbiology, Hebrew University, Israel
Hadar, Y., Department of Plant Pathology and Microbiology, Hebrew University, Israel
Hisdai, A., Department of Plant Pathology and Microbiology, Hebrew University, Israel, Department of Animal Metabolism, Volcani Institute, Israel
Chet, I., Department of Plant Pathology and Microbiology, Hebrew University, Israel
Cotton straw is an unutilized waste product containing 25% lignin, thus making it unsuitable for use as animal feed. This material was found to be an excellent substrate for the growth of the edible mushroom Pleurotus florida. A growth-promoting flavonoid was isolated from the water-soluble fraction of the straw (Platt et al., 1983). After 3 wk of fungal growth on native cotton straw, an 18% decrease in dry weight occurred. Lignin (insoluble in 72% H2SO4) was degraded from the 8th d of growth up to a total of 65% of the original content after 21 d. Prior to lignin degradation, sugars and other water-soluble materials were removed and laccase activity (substrate, 2,6-dimethoxyphenol) was detected. This activity disappeared after the eighth day of growth. In all our experiments it appears that laccase activity precedes the onset of lignin degradation. Cellulase activity reached a maximum after 8 d of fungal growth and immediately disappeared. Total fungal activity was estimated by measuring hydrolysis of fluorescein diacetate (FDA), which indicated a gradual increase during the first 8 d and then reached a plateau. Release of glucose from the straw by commercial cellulase increased with duration of fungal growth from 28 (Μ/g/h-1 to 250 Μg/g/h-1. These results are corroborated by information from artificial rumen experiments showing an increase of in vitro dry matter digestability from 26 to 38%. In comparison, on washed straw, FDA and laccase activity was three-fold smaller. Final dry weight reduction was 10.1%, while total lignin loss was only 33% of the original lignin content. It seems that the water-soluble materials are responsible for the rapid growth, increased enzymatic activity, and total degradation of cotton straw by P. florida. © 1984 The Humana Press Inc.
