Oxalic acid, Fe3+-reduction activity and oxidative enzymes detected in culture extracts recovered from Pinus taeda wood chips biotreated by Ceriporiopsis subvermispora

Pinus taeda wood chips were treated with the biopulping fungus, Ceriporiopsis subvermispora, under solid-state fermentation for periods varying from 7 to 90 days. Low molecular mass compounds and oxidative enzymes were extracted from biotreated wood samples. Manganese-dependent peroxidase was the main oxidative enzyme on all biodegradation periods. Aqueous extracts from biotreated wood presented decreasing pH values, oxalic acid being the major organic acid secreted by the fungus. Analysis of these extracts by gas chromatography coupled with mass spectrometry (GC/MS) revealed small amounts of fatty acids, several short-chain organic acids (C3–C6) and numerous sugar derivatives. 3-methoxy-4-hydroxy benzaldehyde, 3-methoxy-4-hydroxy benzoic acid, 3,4-dihydroxy benzoic acid and tricarboxy-benzene were also found in the wood extracts. A remarkable characteristic of the wood extracts was a strong Fe3+-reducing ability. High Fe3+-reducing activity and high catechol concentrations were detected in the wood extracts from the undecayed control. This reducing activity and catechol concentrations decreased during the first 7 days of biodegradation. However, from the seventh day of culturing, catechol derivatives coming from lignin degradation start to accumulate in the cultures and Fe3+-reduction activity increased again. The Fe3+-reduction activity observed in the wood extracts indicates that Fe2+ would be available in solution during the wood decay process. Considering that Fe2+ and H2O2 (produced by this fungus based on MnP-degradation of oxalate) were present in the wood extracts, at least some extent for degradation reactions based on Fenton-chemistry, similarly to the observed in brown-rot fungi, is supposed to occur during wood decay by C. subvermispora.