Screening And Identify Of Antagonistic Bacteria Against Aspergillus Flavus And Characterization Of The Active Compounds

Many countries have paid highly attention to the food safety issue, the toxins produced by fungi is an important source which caused the food pollution. Aspergillus flavus is the main fungi which pollute product produce, for example peanut. It caused great influence on human and poultry health. The spore of A. flavus could contaminate plant and their products, so that pollute food and feed. Aflatoxin is a kind of highly toxic substances which is widely distributed in the moldy food and products. Especially, peanuts, peanut oil, corn and these products; dairy products and feeds also contain aflatoxin. It is the most toxic mycotoxins which could induce the effects of mutagenic, teratogenic and carcinogenic. It threatens human health and the development of economy seriously.However, existent methods are always limited to control aflatoxins pollutions of crops. Therefore, we hope to find new way to solve these problems.17strains which have obvious antagonistic effect on A. flavus have been screened from the soil in this research. These fermentation products of baeteria could inhibit the growth of A. flavus and degradate aflatoxins effectively. The results mainly include:(1) Based on morphological features, physiological and biochemical test and16SrDNA sequences anaysis,17strains belong to eight groups:Y-21-1-2, Y-32-1-1,Y-32-1-2belong to Bacillus subtilis, Y-1-4belongs to Brevibacterium halotolerans, Y-17-3belongs to Bacillus aerius, Y-8-3, Y-18-2belong to Bacillus altitudinis, Y-41-2, Y-43-2, Y-2-3, and Y-17-1belong to Bacillus thuringiensis,Y-9-1belongs to a Bacillus megaterium, Y-40-1belong to Sporosarcina koreensis,Y-38-3-1, Y-38-3-2, Y-27-2, Y-1-1belong to Lysinibacillus fusiformis. The diversity of antagonistic strains is very rich.(2) The antifungi activity of Y-17-3was obvious, so it was taken to the further research. The active compounds could be precipitated by ammonium sulfate. Antifungal test results showed that the cell-free culture filtrate of Y-17-3could significantly inhibit the growth and spore germination of A. flavus. The activity of antagonism against A. flavus is strongest, when the saturation of ammonium sulfate reaches70%. Its antifungal activity was susceptible after treatment under different pH, and disappeared when the temperature was higher than50℃.(3) Using the coumarin as only carbon resource, aflatoxin degradation strains Y-21-1-2and Y-17-3were selected according to the rate of coumarin degradation. When the aflatoxin was added into culture medium, the rates of aflatoxin degradation by strains Y-21-1-2and Y-17-3were86.7%and90%, respectively, after72hours.