Study On Purification And Lignin Degradation Of Laccase From Echinodontium Taxodii

Echinodontium taxodii has high lignin-degrading ability which depends on itsextracellular laccase. However, few studies focused on characteristics and catalysis of thelaccase from E. taxodii. In this study, the fermentation condition of E. taxodii wasoptimized in order to obtain the maximum enzyme production. The laccase was purifiedand its characteristics were investigated. Besides, the lignin degradation with the laccasewas studied.The optimum medium for laccase producing was as follows: solube starch andtryptone were the best carbon source and nitrogen source with final concentration of1.5%and0.3%respectively, and the C:N is14:1. Veratryl alcohol with concentration of4mMwas added in the culture after4-day fermentation，and the maximum activity of laccasecould reach11.05IU/mL after8-day fermentation.After salting-out, HIC, and anion-exchange chromatography, a purified laccase wasobtained from extracellular fermentation product of E. taxodii. The enzyme was purified23.3-fold to a high specific activity of30.8IU/mg and relatively high yield of38.8%.The molecular weight of the laccase was55.5kDa. The absorption spectrum showed thatit had a typical structure of blue laccase. The enzyme also showed a much higher level ofspecific activity for ABTS than for DMP and guaiacol. The optimum pH and temperaturefor the purified laccase were3.0and60℃respectively. Most ions significantly inhibitedthe laccase activity at high concentration, others like Mn2+, Mg2+didn’t affect the laccaseactivty, no metal ions we studied increased the activity of laccase. Sodium azide stronglyinhibited the laccase activity.For the first time the extracelluar lignin degradation of laccase from E.taxodii wasstudied. The laccase showed a strong lignin degrading ability of breaking the aromatic ring,ether bond β-O-4and methoxy group without any mediators, the hydroxylation of thelignin was also enhanced, which indicated that phenolic hydroxyl groups was easier to bedegraded than non-phenolic hydroxyl groups of lignin. The enzymatic degradation of twolignin model compounds confirmed this assumption.In summary, our result will facilitate the utilization of laccase in biomass and ligninmodification.