Detection and quantification of oxalic acid from the brown-rot decay fungus, Postia placenta

The mechanism by which brown-rot fungi initiate depolymerization of holocellulose in wood remains unknown, Recently, oxalic acid has received considerable attention in cellulose breakdown by brown-rot fungi. The oxalic acid could serve as a proton donor for hydrolytic or an electron donor for oxidative (Fenton's reaction-H2O2/Fe2+) cleavages of cellulose. The acid may originate via oxaloacetase action upon oxaloacetate. We report the applications of HPLC and oxalic acid kit colorimetry to quantify oxalic acid from hyphae grown on southern pine wood blocks (WBs) or in liquid culture. Oxaloacetase activity was not observed in either Amicon YM10 (MW cut-off, 10,000) filter-retained intra- or extracellular fractions of liquid cultured hyphae or in homogenates from decayed WBs. In contrast, oxalic acid was detected by HPLC in both P. placenta liquid cultures and decayed WBs. The less sensitive, oxalic acid, spectrophotometric kit (mg vs. mu g) did not detect oxalic acid in liquid cultures. These results constitute additional evidence for an oxalic acid-Fe2+/H2O2-Fenton's mechanism for brown rot-induced cellulose degradation. However, the origin of oxalic acid was not established.