Improvement of lignin-degrading enzymes production from the white-rot fungus (Lentinus strigosus) and its application in synthetic dye removal

Abstract

Cultivation of Lentinus strigosus, a white-rot fungus producing a ligninolytic enzyme, in a simple medium indicated the production of Lac and MnP in the secondary growth phase. The aim of this study was to optimize the nutrient composition for Lac and MnP production as well as to investigate the removal of synthetic dyes by the strain. Preliminary study showed cellobiose and L-asparagine as the suitable nutrient sources for highest Lac and MnP production. To enhance the production of these enzymes, the L9 Taguchi design was employed to optimize the culture medium composition. The optimized medium (1 L) containing 15 g cellobiose, 0.3125 g peptone, 1.2500 g L-asparagine and 0.002 g CuSO4gave Lac and MnP activities of 33,955.83 and 3,764.57 UL-1, respectively. The data also suggested L-asparagine had the largest influence on enzymes production. Further study showed that 0.9375 gL-1 L-asparagine was the best concentration, giving maximum Lac (35,977.76 UL-1) and MnP (1,838.49 UL-1) activities. Removal of different structural synthetic dyes by L. strigosus was investigated. Less than 6% RBBR remained following 48 h of fungal cultivation, whereas RB5 was more slowly removed, requiring 96 h for 98% removal. Maximum removal (82%) of Indigo 4B was achieved in 8 d which was the slowest among the tested dyes. Furthermore, it was found that the increasing percentage of dye removal was in accordance with the increase in enzymes activities. In summary, it was clear that L. strigosus efficiently removed these dyes, and Lac and MnP were considered as the major enzymes involved in this process. Key words: Lentinus strigosus, white-rot fungus, laccase, manganese peroxidase, reactive dye.