Effect Of Rare Earth Elements On The Production Of Laccase By Pycnoporus Sp.SYBC-L3 And The Study Of Decolorization Of Azo Dyes By Laccase

White rot fungi,which widely exist in nature,are the main producing fungi of laccase.The expression of laccase in white rot fungi is generally regulated by metal ions.However,there are few reports on the effects of rare earth metal ions on laccase production by white rot fungi,and the mechanism of which is also unclear.In this paper,the effects of different rare earth ions on laccase production in Pycnoporus sp.SYBC-L3 were studied,and the possible mechanism was investigated.The decolorization of Acid Red 1?AR1?,Reactive Black 5?RB5?and Reactive Violet 5R?RV5R?by lac-L,the laccase produced by Pycnoporus sp.SYBC-L3,was also investigated.The main results were as follows:?1?The production of laccase by Pycnoporus sp.SYBC-L3 was generally promoted by samarium ion(Sm³⁺),lanthanum ion(La³⁺),gadolinium ion(Gd³⁺)and erbium ion(Er³⁺)at relatively low concentration(0.1 mmol·L^-1?0.5 mmol·L^-1)and inhibited at relatively high concentration(5 mmol·L^-1).In addition,rare earth ions had no promoting effect on the enzyme activity of laccase,and rare earth ions of 5 mmol·L^-1 generally have a significant inhibitory effect on the enzyme activity of laccase.?2?Sm³⁺could inhibite the growth of Pycnoporus sp.SYBC-L3.The proportion of laccase in the extracellular protein and the laccase yield per unit weight of mycelium increased with the increasing concentration of Sm³⁺within the range of 0.1-0.5 mmol·L^-1.?3?Sm³⁺could cause oxidative stress of Pycnoporus sp.SYBC-L3,and the increase in laccase yield under Sm³⁺stress may be related to oxidative stress induced by Sm³⁺.?4?The optimum conditions for decolorization of three azo dyes by lac-L were as follow:employing 1-Hydroxybenzotriazole as mediator,reaction temperature at 50?,pH at 4.0?AR1,RV5R?or 5.0?RB5?and 1 U·mL^-11 of laccase dosage.Under the optimized conditions,AR1 and RV5R were almost completely decolorized,with decolorization rates of 96.1%and97.8%,while decolorization rate of RB5 was 83.8%.?5?Plant toxicological experiments showed that the three dyes significantly inhibited the germination rate,radical and plumule growth of wheat and rice seeds.However,the degraded dyes had no inhibition on the germination rate of wheat and rice.Simultaneously,the inhibitory effect of degraded dyes on the growth of radical and plumule was also reduced compared to undegraded dyes.?6?The degradation products of RV5R were analyzed by gas chromatography-mass spectrometry,and three degradation products were detected.It was speculated that the three substances were 3-phenylpropanoic acid,2-benzenesulfonyl-ethyl sulfate and 2-?2-carboxyl-ethyl?-6-hydroxy-benzoic acid,respectively.The former two are final degradation products,while the third one is intermediate product.