Spawn-based pellets of Pleurotus ostreatus as an applied approach for the production of laccase in different types of water

In recent years, oxidoreductase enzymes such as laccases have received considerable attention for their ability to degrade and eliminate organic micropollutants from contaminated water in a process known as enzyme-based wastewater treatment. Thus, methods to produce high laccase activity in water are a point of focus, with white-rot fungi being highlighted as a tool in this context. This study, therefore, explored the applied approach of direct addition of mushroom spawn of the white-rot fungi Pleurotus ostreatus into water and its potential for laccase production under different conditions. Grain spawn was observed to be preferable to sawdust spawn, resulting in laccase activity of 53.9 ± 5.9 U/L and 4.8 ± 0.8 U/L, respectively. Laccase activity was induced by adding kraft lignin (4 g/L), and an eightfold increase to 446.3 ± 43.1 U/L was observed for grain spawn. Lignin accumulated in the spawn over time, resulting in brown pellets composed of spawn, mycelium and lignin. Our results demonstrated that high levels of laccase activity could be obtained in different types of water, including effluent municipal wastewater, using this method. No impact from the addition of inorganic nitrogen (ammonium nitrate, N-levels 14 mg/L, 140 mg/L) or organic nitrogen sources (urea, yeast extract, wheat bran, N-levels 14 mg/L, 140 mg/L) was observed for the treatment with grain spawn and lignin, suggesting that stable laccase activity can be expected under these nutritional conditions.