Biotransformation of Kraft lignin by Pleurotus ostreatus Florida in conditions optimized for laccase production

Abstract

Abstract White-rot fungi are efficient degraders of the lignin moiety due to the production of extracellular enzymes that includes the laccases which are able to depolymerize lignin oxidative processes to low-molecular weight phenolic and aromatic compounds. These end-products have important industrial applications, as building blocks for chemical syntheses of high-value. Thus, the objective of this work was to optimize the culture conditions for laccase production by Pleurotus ostreatus Florida grown on Kraft lignin, and to evaluate lignin biodegradation products. The fungal strain produced optimum laccase titers after evaluation in a 33-factorial statistical design by varying: lignin concentration, yeast extract and time of cultivation. The extracellular fluid obtained under the optimized culture condition was treated by liquid-liquid partition with ethyl acetate in order to determine the lignin degradation products by LC-MS/MS. Concentration of lignin was the main variable that increased laccase production assayed against substrate 2,6-dimethoxyphenol. Optimal laccase production predicted by the model was 5.73 U/mL under the condition: 0.87% (w/v) lignin, 4.5% (w/v) yeast extract and 10 days cultivation. The experimental laccase titer obtained following optimal conditions was 5.68 U/mL. The lignin metabolites identified were 4-methoxycinnamaldehyde and cuminaldehyde. In addition, abscisic acid was produced; considered a stress-related hormone product of the fungus. These findings show a suitable source of fungal laccase for obtaining new metabolites from the biodegradation of Kraft lignin by fermentation.