Degradation Characteristics Of AFB₁ And OTA By Luteimonas Sp.CW574 And Its Biodetoxification Application

Mycotoxins are secondary metabolites produced by some toxic fungi with low molecular weight,stable chemical structure and toxic effects.Mycotoxins not only seriously threaten the animal production and human health,but also caused huge economic losses to the animal husbandry and food industry.Aflatoxin B1(AFB1)and ochratoxin A(OTA)are the most harmful and widely distributed mycotoxins.As a natural pollutant,the pollution of mycotoxin is difficult to eliminate.The study on biological detoxification technology emerged as the times require.The study on detoxification technology is great significant to food safety,human health and sustainable agricultural development.For the limitations of physical and chemical detoxification,such as nutrient loss,incomplete detoxification and secondary contamination,these two types of technologies cannot be widely used.The biological detoxification method has been developed rapidly in recent years.It has the advantages of mild active conditions,safety and environmental friendly.It is an ideal method for detoxification.In this study,a difunctional strain(Luteimonas sp.CW574)with OTA and AFB1 degradation activities was screened and the degrading characteristics were incestigated.The strain CW574 degradation ability for corn soybean meal feed was evaluated.The results showed that the degrading strain could effectively degrade OTA and AFBi under the condition of low concentration of toxin.The bacterial solution of strain CW574 was inoculated into the nutrient broth(NB)medium of OTA and AFB1 respectively.After the strain co-cultured with OTA for 120 h,the degradation ratio reached about 75%,when the strain co-cultured with AFBi for 96 h,the OTA degradation ratio reached about 67.0%.The degradation activities of OTA by cell suspension of strain CW574 at 30?,and the degradation activity of AFB1 by cell-free culture at 80? was significantly higher than that of co-cultured strain system.OTA and AFBi with concentrations of about 40 p,g/L could be completely degraded within 3 h and 24 h by the above degradation agents,respectively.The degradation of the two toxins by cell-free supernatant,cell weight suspension and intracellular crude enzyme solution of strain CW574 was studied.The results showed that the bioactive substance of OTA degradation for CW574 existed in the cell,and the bioactive substance for AFBj degradation was in the cell-free supernatant.The optimum reaction conditions showed that the optimum temperature of OTA degradation by strain CW574 was between 20? and 50?,and the optimum pH value was between 5-8.The degradation activity of CW574 to AFBi was gradually increased by temperature elevation,and the degradation ability was even very stable at temperature of 80?.When the temperature was 80?,the degradation ratio(99%)was the higher than other incubation temperatures.The degradation activities of OTA and AFBi was significantly inhibited by Fe3+,Cu2+,Ca2+and Zn2+with final concentration of 0.1 mol/L at pH 8.0.The results of enzyme inhibition test showed that the metal chelating agent EDTA,EGTA had no significant inhibitory effect on the degradation of OTA,but had significant inhibitory effect on the degradation of AFBi in varying degrees.SDS treatment,protease K treatment,co-treatment of SDS and protease K and heating treatment significantly inhibited the degradation of OTA.Heating treatment significantly promoted the degradation of AFB1.Protease K treatment showed no significant effect on the degradation of AFB1,and SDS,SDS plus protease K treatment showed significant inhibitory effect on the degradation of AFB1.It was concluded that the bioactive substance of OTA degradation by strain CW574 was derived from intracellular protease,and the degradation ability of strain CW574 for AFBi might not only come from biological enzymes,but also from other small molecules.The cultured bacterial solution was mixed with the corn and soybean meal feed which containing 80 ?g/kg of OTA and 80 ?g/kg of AFBi,and the detoxification activity to the pollution feed was evaluated.The results showed that the corn and soybean meal feed treated with CW574 could significantly reduce the residual concentrations of OTA and AFB1 in the feed.When the degrading strain was thoroughly mixed with the feed and incubated for 120 h,nearly 80%of the OTA and 50%of the AFB1 in the polluted soybean meal feed were degraded.The culture solution of the degraded strain has obvious detoxification effect on the artificially contaminated two kinds of Aspergillus spp.produced toxins in the corn-soybean-type feed,and the difunctional strain has the potential for subsequent development of the feed detoxification agent.