Fungal activities involved in lignocellulose degradation by Pleurotus

Abstract

During growth of Pleurotus on cotton straw both the straw in general and the lignin in particular were degraded. After 4 days of fungal growth, activity of laccase, catechol oxidase, peroxidase, and cellulase were detected. This activity, however, declined rapidly after 8–10 days of growth. Lignin degradation began after 10 days and reached a maximum after 21 days. It would seem that the preliminary action of laccase is a prerequisite for lignin degradation. The Pleurotus ostreatus strain ‘P3’ had no detectable laccase activity and showed very poor ability to degrade cotton straw and lignin. Water extract of cotton straw was found to be a potent inducer of laccase in liquid medium and had an effect much stronger than several small phenolic compounds. The degradation of washed cotton straw and lignin from this straw was lower than native straw, so was laccase activity on this medium. High carbon dioxide concentrations encouraged straw degradation by P. ostreatus ‘florida’ but severly limited lignin degradation. Other fungi including the known lignin degrader Phanarochaete chrysosporium were able to degrade up to 40% of cotton straw dry weight within 21 days of fungal growth. The percentage degradation of lignin, however, was very low (only 10% in 21 days). Pleurotus ostreatus ‘florida’ was able to degrade up to 56% of the lignin within this time. After treatment with P. ostreatus ‘florida’ almost four times as much glucose was released when the straw was treated with commercial cellulases, showing increased availability of cellulose. It is suggested that treatment with P. ostreatus ‘florida’ may be used to enrich low value food materials for ruminant animals.