Tropical wood-decaying fungi as a means of conversion of agricultural plant residues: Influence of the incubation temperature on the activities of ligninolytic enzymes

Abstract

The digestibility of agricultural plant residues in the rumen of domestic animals is restricted by the lignin content of the material. Selective delignification using ligninolytic microorganisms in a solid state fermentation process may help to overcome this problem. The aim of this work was to determine the influence of the incubation temperature on the production of extracellular ligninolytic enzymes and the degradation of lignocellulose by selected tropical fungi. Four wood-inhabiting fungi, Auricularia sp., Coriolus versicolor, Lentinus edodes and Polyporus sp., were grown on wheat straw for five weeks at 18°C, 25°C or 30°C, respectively. The activities of extracellular ligninolytic enzymes (laccases and manganese peroxidases) were assessed weekly. In addition the substrates were analysed with regard to the in vitro digestibility, the loss of organic matter and lignin. Generally higher incubation temperature enhanced the colonization of the straw substrate by the fungal mycelium and the increase of enzymatic activities. Moreover the highest enzyme levels were usually found at 30°C. Only L. edodes displayed highest enzyme activities at 18°C or 25°C. Loss of organic matter and loss of lignin were highest at 30°C, with the exception of L. edodes (25°C temperature optimum). C. versicolor degraded more lignin compared to the other fungi tested (69% of initial after 5 weeks). High degradation of lignin and in vitro digestibility along with relatively low degradation of other straw components was performed by Auricularia sp. and L. edodes at 25°C, which makes these fungi seem promising with regard to selective delignification of plant waste materials.