Basic Research On Laccase Production With Trametes Versicolor And Its Application In The Degradation Of Organic Pollutants

Laccase is a type of multi copper-containing polyphenol oxidases capable of oxidizing a wide range of aromatic compounds.It is a kind of environmental friendly green catalyst which has received numerous interests in industrial application.In this work,the solid-state fermentation of T.versicolor laccase,and the application of T.versicolor and laccase in the degradation of organic pollutants were investigated.The major results were as follows:The laccase production by T.versicolor was studied under solid-state fermentation.Results show that corn straw was the suitable substrate for laccase production.The optimized fermentation conditions:water content of substrate 65%,initial pH 4.5-6.0,fermentation temperature 30?,and inoculation dosage 10%.The laccase activity was enhanced by the addition of 0.5%glucose.Under the optimum conditions,the activity of laccase could reach 32.09 U/g after 10 d.The effects of primary factors on the degradation of bisphenol A were analyzed.Results show that the degradation rate of bisphenol A degraded by laccase was improved with the increase of reaction time and laccase dosage;the optimized degradation conditions:pH 5.0,temperature 50?,rotate speed 120 r/min.Mediators acetosyringone and ABTS showed effective enhancement on the degradation of bisphenol A.Metal ions Cu²⁺,Zn²⁺ and Co²⁺ nearly showed no effect on bisphenol A degradation;however,10 mM Fe²⁺ and Fe³⁺ substantially inhibited the degradation of bisphenol A.1%of organic compounds?acetone,isopropanol,xylene,methanol,acetonitrile,and diethyl ether?did not affect the degradation of bisphenol A;however,10%of acetone,isopropanol,xylene and methanol significantly inhibited the degradation of bisphenol A.Simultaneous production of laccase and degradation of bisphenol A by T.versicolor under solid-state fermentation was studied.Results show that,in the process of laccase production under solid state fermentation,T.versicolor can effectively degrade the bisphenol A and laccase production was enahnced by the addition of bisphenol A.The pH range of bisphenol A degradation with T.versicolor was broader,and metal ions(10 mM Cu²⁺,Zn²⁺,Co²⁺,Fe²⁺ and Fe³⁺)hardly affected the degradation rate of bisphenol A;moreover,without the addition of mediators?ABTS and acetosyringone?,the degradation rate of bisphenol A was up to 90%.The herbicide isoproturon is easily accumulated in the soil and results in the environmental pollution.The isoproturon degradation with T.versicolor laccase-mediator systems was invesgitated.Results show that the degradation rate of isoproturon degraded by the laccase alone was less than 10%,due to the presence of the relatively strong withdrawing electron group?-NH-CO-N?CH3?2?in the chemical structure of isoproturon.Compared with natural mediators,synthetic mediators were more effective in the laccase-mediated degradation of isoproturon.However,laccase activity rapidly declined in the presence of the synthetic mediator HBT.The optimum pH of isoproturon degradation with the laccase-HBT system was 5.0,and the optimal temperature was 50?;metal ions Cu²⁺,Zn²⁺ and Cd²⁺ positively enhanced the isoproturon degradation.Polyethylene glycol?PEG?can enhance the degradation rate of isoproturon with the laccase-HBT system,moreover,PEG can reduce the HBT dosage,broaden the pH range,and not change the optimum temperature.Through the identification of transformation products using GC-MC,oligomerization was the major mechanism of isoproturon degradation with the laccase-HBT system.The results in this study are of great value in the field of bioremediation of polluted environments.