IMPROVEMENT OF LACCASE PRODUCTION AND ITS CHARACTERIZATION BY MUTAGENESIS

In this study, laccase production was enhanced using mutant Shiraia sp. The Shiraia sp. GZS1 strain was mutated using ultraviolet irradiation, followed by screening of strains that were resistant to certain stressors. The mutant GZ11K2 was selected and used for further studies. 2,2-Azino-bis(3-ethylben-zothiazoline-6-sulfonate) was used as substrate for both wild and mutant laccases at optimal pH (4.0). The mutant laccase exhibited a broader active pH range. The mutant laccase also showed a higher optimal catalytic temperature, more active under alkaline conditions, and higher temperature range than the wild one. The mutant strains produced higher yield of laccase than the wild strain even at high salinity of 3g/L NaCl. Both laccases were mildly inhibited by sodium dodecyl sulfate (0.5mM), ethanol (50%) and ethylenediaminetetraacetic acid (1mM), and almost completely inhibited by NaN3 (20M) and DTT (1mM), stable in the presence of metal ions except Ag+ and Hg2+. Practical ApplicationsLaccase is extensively used in various applications, such as pulp delignification, decoloration, biopolymer modification, biotransformation and food dechlorination. A newly isolated laccase-producing strain Shiraia sp. GZS1 and a genetically stable mutant GZ11K2 were established with 1.82 times laccase activity compared with that of the wild strain. The mutant Shiraia sp. GZ11K2 laccase was active over a wider pH and temperature ranges and more stable than the wild strain under neutral and alkaline conditions. The laccase from the mutant GZ11K2 with higher laccase productivity and enhanced enzyme properties can be used in biotechnological and industrial applications.