Degradation of ¹⁴C-labelled poplar wood lignin by selected white-rot fungi

Summary

Of eight white-rot fungi examined, seven fungi grew on nitrogen-limited poplar wood meal medium and degraded ¹⁴C-lignin in wood meal to ¹⁴CO₂. Increased oxygen enhanced both the rate and extent of degradation. However, whereas Pleurotus ostreatus, Pycnoporus cinnabarinus 115 and Pycnoporus cinnabarinus A-360 degraded 12–17% of ¹⁴C-(U)-lignin of poplar wood to ¹⁴CO₂ also in an air atmosphere, Sporotrichum pulverulentum, Phlebia radiata 79 and Phanerochaete sordida 37 degraded only 1–5% under these conditions. Addition of cellulose and glucose to the poplar wood medium stimulated degradation of ¹⁴C-(RING)-lignin of poplar wood by Phlebia radiata 79 but repressed degradation by Polyporus versicolor and Pleurotus ostreatus. Cellulose added to the wood meal medium had no effect on the degradation of lignin by Phanerochaete sordida 37 and Sporotrichum pulverulentum but glucose slightly repressed lignin degradation by these fungi. Those white-rot fungi which were considered as preferentially lignin attacking fungi could degrade ¹⁴C-(RING)-lignin of poplar wood efficiently under 100% oxygen. They did not require an extra energy source in addition to wood meal polysaccharides for rapid ring cleavage and they degraded up to 50–60% of the ¹⁴C-lignin to ¹⁴CO₂ in 6–7 weeks at a maximum rate of 3–4% per day.