Effect of pH and Temperature on the Growth and Laccases Production in the Cultivation of Pleurotus sajor-caju PS-2001 in Stirred-tank Bioreactor

Background: Laccases are multi-copper enzymes that oxidize phenolic/aromatic compounds and represent a promising alternative to environmental decontamination processes and biotechnological applications. Objective: The effects of pH and temperature on the growth and the production of laccases during the cultivation of Pleurotus sajor-caju PS-2001 in stirred-tank bioreactor were assessed. Methods: Assays were performed at fixed pH values from 4.5 to 7.5 (28°C) and at temperatures from 24 to 36°C (pH 6.5). Results: In pH testing, larger biomass concentration (4.5 g L-1) was reached at pH 5.5, whereas concentrations of 3.7, 3.1 and 1.7 g L-1 were measured at pH 4.5, 6.5 and 7.5, respectively. With ABTS as substrate, peaks of laccases activity of 50, 30 and 24 U mL-1, at pH 6.5, 5.5 and 7.5, respectively, were detected. Under different temperatures, higher mycelial concentrations (3.0 g L-1) were quantified at 66 hours at 28°C, while concentrations below 2.0 g L-1 were observed at 24, 32, and 36°C. Maximum laccases activities of 50, 42, 6 and 5 U mL-1 were obtained at 28, 32, 24, and 36°C, respectively. In all tests, the presence of other phenol oxidases – total peroxidase, manganese peroxidase, lignin peroxidase and veratryl alcohol oxidase – was observed. Conclusion: The results indicate that variations in pH and temperature during fungal cultivation strongly affect the enzymatic activity and growth kinetics of P. sajor-caju PS-2001 in a stirredtank bioreactor.