Degradation of [14C]Lignin-labelled Wheat Lignocellulose by White-rot Fungi

Abstract

[lignin-,14C]Lignocellulose was prepared from wheat seedlings, injected with l-[U-14C]-phenylalanine, by a procedure that selectively removed radiolabelled low molecular weight compounds and protein. 14C was mainly localized in the acid-insoluble fraction (Klason lignin) of the lignocellulose and the polymeric nature of the radiolabelled material was confirmed by gel permeation chromatography. Ferulic and p-coumaric acids were found to be esterified to both carbohydrate and lignin fractions of the wheat lignocellulose, but contained only a small proportion of the total 14C. The white-rot fungi Phanerochaete chrysosporium, Sporotrichum pulverulentum and Coriolus versicolor degraded the radiolabelled substrate; the S. pulverulentum culture was the most active, releasing almost 50% of the 14C as 14CO2 in 15 d at 37 °C. In all three species 14CO2 evolution commenced after a lag period during which growth occurred, and was greatly enhanced by reducing the nitrogen concentration in the medium. This indicated that grass lignin degradation by these fungi is subject to the same nutrient nitrogen regulation as the degradation of wood and synthetic lignins. In a culture of P. chrysosporium grown on the radio-labelled substrate for 50 d at 37 °C, 14CO2 was the main product. Low molecular weight degradation products present in the culture medium were acid-soluble and accounted for a much smaller proportion of the original [14C]lignin.