Study On Screening Of Sphingobium Sp.B2 And Its Zearalenone Degradation Characteristics And Application

Zearalenone(ZEN)is a highly contaminated and influential fungal toxin which is commonly found in corn,wheat,rice and other crops and processed grains.ZEN is a kind of secondary metabolite produced by Fusarium sp.It has cytotoxicity,reproductive toxicity,hepatorenal toxicity,etc.After eating ZEN,humans and and livestocks will produce variety of adverse reactions,such as infertility and even abortion.At present,the methods of detoxifying ZEN include biological method,physical method and chemical method.In this study,biological methods were used to detoxify ZEN,ZEN degradation bacteria were screened,and their degradation characteristics were studied.Firstly,samples were collected for ZEN enrichment culture,and eleven strains with ZEN degradation activity were obtained by screening and isolating.Then,from these strains,strain B2 was selected for in-depth study,for it can degrade 5 mg/L ZEN in 8 hours and showed stable ZEN degradation ability.Based on the morphological characteristics and the phylogenetic status,strain B2 was finally identified as Sphingobium sp.The mice were fed with the fermentation broth of B2 to determine the acute toxicity of strain B2.The results showed that the mice did not die within 14 days and grew normally.The optimal growth conditions and ZEN degradation conditions of strain B2 were studied.The results showed that the optimal growth conditions of strain B2 were:temperature is 30℃,pH 7.0 and suitable for growth under good ventilation conditions.Suitable carbon source is maltose and glucose,and suitable nitrogen source is organic nitrogen source.The tolerance to sodium chloride is not high,when the concentration of sodium chloride is higher than 20 g/L,the growth of strain B2 was significantly inhibited.In MM liquid culture media,the ZEN degradation rate by strain B2 reached higher than 98%at 30℃ in 8 hours,the optimal ZEN degradation temperature was 30℃,the optimal ZEN degradation pH was 6.0-7.0,and the optimal inoculation amount is 5%.Strain B2 had good ZEN degradation effect when ZEN concentration was below 25 mg/L.The location and characteristics of the ZEN degrading substances in strain B2 were studied.The results showed that the ZEN degrading active substance in strain B2 was located in the culture supernatant.After high-temperature inactivation and proteinase K treatment,the ZEN degradation activity was significantly decreased,which infered that the ZEN degrading substance in strain B2 is a protein secreted extracellularly.And this protein is a constituent enzyme which was not induced by ZEN.In M9 medium,cultured at 30℃for 48 hours,the ZEN degradation activity of strain B2 reached the highest,and the molecular weight of ZEN degrading enzyme was between 30-50 kDa.The toxicity of the degradation product to MCF-7 cells was investigated,and the estrogen toxicity of the degradation product ZEN by strain B2 was significantly reduced.The ZEN detoxification application of strain B2 in feed was investigated.The results showed that strain B2 had a very good ZEN degradation effect for feeds contamined with ZEN concentration in the range from 500-5000 μg/kg,over 80%ZEN could be degraded after adding strain B2 to corn grits for 48 hours.Strain B2 also showed excellent ZEN degradation activity for corn grits,corn flour and DDGS feed from different sources.More than 70%ZEN could be degraded in corn grits and corn flour feed in 2 days,and 60%ZEN could be degraded in DDGS feed in 7 days.Therefore,the strain B2 has good application prospect of being developed into ZEN degrading bacteria agent or enzyme.