A comparison of lignin oxidation, enzymatic activity and fungal growth during white-rot decay of wheat straw

This paper reports a laboratory study where multiple variables have been monitored in parallel as a function of white-rot incubation time. A model system with Pleurotus ostreatus growing on unamended wheat (Triticum aestivum) straw under solid-state cultivation conditions was used to investigate changes in lignin oxidation, amounts of the fungal biomarker ergosterol and activity of manganese peroxidase (MnP) at regular intervals over 84 days. Lignin oxidation was monitored with thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) where 3,4-dimethoxybenzoic acid, methyl ester (G6) to 3,4-dimethoxybenzaldehyde (G4) [Ac/Al]G and 3,4,5-trimethoxybenzoic acid, methyl ester (S6) to 3,4,5-trimethoxybenzaldehyde (S4) [Ac/Al]S were used as relative lignin decomposition state proxies. [Ac/Al]G, [Ac/Al]S and ergosterol production show little change during the first 21 days of incubation. MnP activity, however, rises rapidly and peak activity is reached during the same time interval. This is followed by an increase in both [Ac/Al]G, [Ac/Al]S and ergosterol formation where most of the increase in these variables takes place after 21 days. Therefore a rapid early rise in manganese-dependent peroxidase activity precedes significant changes both in lignin oxidation and fungal growth. We have demonstrated that it is possible to analyse lignin oxidation using THM in the presence of TMAH and, in the same system, measure enzyme activity and amounts of fungal biomarkers as a function of incubation time. This approach will be useful when investigating compositional changes in litter and soil layers.