Screening Of Aflatoxins B₁ Degrading Bacteria And Preliminary Study On Its Degradation Properties

Aflatoxin B1(AFB1)is one of the most toxic and harmful mycotoxins in commonly existed in mouldy cereal grains and feedstuff,which is a serious threat to their using safety and economy value.Excessive intake of aflatoxin can also seriously threat the health of human beings and animals.Researching the detoxification mechanism to reduce AFB1 in mycotoxin contaminated cereal grains and feedstuff has great application value and is a potential approach to their further utilization.Although the traditional physical and chemical method can reduce some of aflatoxin,its mechanism and reaction conditions are too intense,which will bring secondary pollution or seriously influence nutritional value and quality of cereal grains and feedstuff.Therefore,the biological detoxification with higher efficiency and less pollution has become a hot research topic.In this study,35 strains which plants can grow well have been screened by using the soil culture medium containing coumarin as the only carbon and nitrogen source.After second screening,9 microbial strains with AFB1 degradation capacity of above 60%were selected,one strain of which,named YM-1,has the AFB1 degradation capacity of 91.46%determined to be the target strain for further study.The strain YM-1 was identified as Pseudomonas aeruginosa by 16S rDNA sequence comparison and judgment of bacterial colonies properties and dyeing identification.The degradation dynamics of AFB1 by P.aeruginosa YM-1 showed that 90.70%of AFB1 in NB medium was degraded after 96 h and the degradation rate of AFB1 was the highest between 24 h to 36 h,and up to 82.99%in 48 h.The AFB1 degrading activity of P.aeruginosa YM-1 was predominantly attributed to the cell-free supernatant and the P.aeruginosa YM-1 cell could also adsorb some AFB1.The AFB1-degrading activity in the cell-free supernatant was found sensitive to proteinase K,but the heat treatments was not affected.The separation of degradation active components in the supernatant of YM-1 were carried out by method of sulfuric acid precipitation and anion exchange chromatography.The preliminary separation that 0-40%saturation of ammonium sulfate precipition in YM-1 supernatant showed the performance of degradation,but the AFB1 degradation active components can not be separated by anion exchange chromatography.Furthermore,it was found that the extracellular polysaccharides in the supernatant of YM-1 had the activity of degrading AFB1,with the degradation rate of 56.92%.The study of degradation in mouldy corn powder showed that solid state fermentation of the P.aeruginosa YM-1 was performed and 88.87%of AFB1 in mouldy corn powder was reduced after 6 days.This study provides an experimental basis for the detoxification treatment of AFB1 contaminated cereal grain and feedstuff by P.aeruginosa.