Screening Of High-producing Laccase Plurotus Ostreatus Strains And Their Degradation Of Aflatoxins

Aflatoxin B1 is a secondary metabolite produced by Aspergillus flavus and Aspergillus parasiticus.It is one of the most toxic mycotoxins and belongs to class I carcinogens.It is widely found in crops such as corn,peanuts,and has the effects of causing cancer and mutagenicity in humans and animals.Aspergillus flavus is an important pathogenic fungus in the cultivation of oyster mushroom Pleurotus ostreatus,causes the decline of the yield and quality of Pleurotus ostreatus.This study aims to screen out high laccase producing Pleurotus ostreatus strains,their ability to degrade aflatoxin B1 effectively and their antagonistic ability against Aspergillus flavus.This study provides a theoretical basis for the green and safe production of oyster mushroom and the treatment of contaminated aflatoxin in agricultural products.The following results were obtained:1.The laccase producing strains of oyster mushroom were screened by plate tests using the indicator compounds guaiacol,tannic acid and ABTS.According to the characteristics of oxidation ring/hyphae circle size and color change,eight high laccase-producing strains were screened from twenty-four strains of Pleurotus ostreatus,while two strains of P6 and P20 were finally selected by the determination of laccase activity in liquid fermentation.2.The degradation of AFB1 was carried out by using the fermentation broth of Pleurotus ostreatus P6 and P20.It was found that the initial degradation rate of AFB1 in the fermentation broth of P6 and P20 strains were 86.4%and 72.12%respectively.After adding Cu2+ and surfactant Triton X-100 separately in strain of P6 fermentation broth,AFB1 degradation ability increased to 90.43%and 92.88%respectively.Tween 20 has a certain inhibitory effect on the degradation of aflatoxin B1 in the fermentation liquid of P6 Pleurotus ostreatus.There is a positive relation between laccase activity and the degradation rate of aflatoxin B1.That is higher the enzyme activity,stronger is the ability to degrade toxins.3.Ten Aspergillus flavus strains were isolated from soil of corn fields,which were identified by moiphological and molecular methods.The toxin-producing ability of strains were detected by colony color method.It was found that two strains of AF02 and AF03 failed to produce any aflatoxins,other aflatoxins producing strains were analyzed for their toxins producing ability by HPLC after cultivation on YES media,only AF13 strain produced aflatoxin AFB1,AFB2,AFG1 and AFG2,the other 7 strains produced aflatoxin AFB1 and AFB2,strain AF08 produced the highest AFB1value as 3.553μg/g.4.The highest aflatoxin-producing strain AF08 was used as the target to screen the aspergillus resistant Pleurotus strains.A significant antagonistic ability of different Pleurotus strains was observed to inhibit the growth of toxigenic Aspergillus strain.Pleurotus ostreatus strains P3,P5,P17,P18,P19,P21,P23 and P21 had no antagonistic ability against AF08 as Aspergillus flavus quickly covered the mycelium of Pleurotus ostreatus and produced a large number of spores.However,Pleurotus ostreatus strains P2,P4,P9,P15,P16 and P20 could completely cover the growth of Aspergillus mycelium,thus they are highly resistant to Aspergillus flavus.