Improved production of laccase by Daedalea flavida: consideration of evolutionary process optimization and batch-fed culture

Abstract

The genetic algorithm was used effectively to find the optimal values of eight process variables for the maximum laccase production by Daedalea flavida in a stationary culture. The algorithm was modified suitably to improve laccase production with 18 parallel experiments in 4 generations. A high enzyme titer of 65 % was achieved after the optimization and compared to the titer obtained before optimization. To study the effect of the surface immobilized growth on the enzyme production, the fungus was grown on three solid carriers. When cultured on polymer composite fibers, polyurethane foam, or steel wool, at least 2.5 times more biomass was produced, compared to the biomass produced in support-free growth. On the contrary, the mycelia grown on solid support produced much less laccase than non-adhering mycelia. Four parallel runs of batch-fed cultures were done, using the cell mass of D. flavida to evaluate the influence of four different volumes of medium exchanged on laccase production. For sustainable production of the enzyme, complete exchange of medium was favorable, where the laccase activity increased continuously in six consecutive cycles, though, 50 % exchange of medium produced the maximum laccase in terms of mean enzyme activity obtained in six cycles.