Isolation And Characteristics And Preliminary Application Of Two Zearalenone-Degrading Bacteria

Zearalenone(ZEN),also known as F-2 toxin,was isolated by Stob from the corn that was contaminated by Fusarium graminerum.It belongs to the class of dihydroxybenzolactone compounds and has been found to have at least 15 derivatives now.Zearalenone existed widely in moldy wheat,corn and other grains.It can accumulate in grains,causing economic losses and inducing risks to the health of animals and humans.Zearalenone and its derivatives are similar to estrogen in their structures,which results that they can bind to estrogen receptors and have reproductive toxicity.In addition,they also have cytotoxicity,immunotoxicity,genetic toxicity,organotoxicity and carcinogenicity.Therefore,it is particularly important to study how to eliminate zearalenone safely and effectively.At present,eliminating zearalenone by biological degrading method is a research hotpot.This thesis consists of four parts.The first part is isolating bacteria that can degrade zearalenone from the soil samples collected from Nanjing,Jiangsu Province by using zearalenone as the only carbon source,and enrichment culture.Finally,we succeeded in screening two strains named HA-1 and HR-1 which have the ability degrading zearalenone from the soil samples.After the morphology,physio-biochemical characteristics and molecular identification,the strain HA-1 was identified as Aeromicrobium sp.,and the strain HR-1 was identified as Rhodococcus sp..The ZEN degradation rates of these two strains were higher than 95%.The second part studied their optimal growth conditions and ZEN degradation conditions of HA-1 and HR-1.The results showed that the optimal temperature,pH and NaCl concentration for the growth of the degrading bacteria HA-1 were 30℃,pH 7.0-8.0,and 7 g/L.The strain HA-1 can use sorbitol,lactose,fructose and peptone as carbon source and can also use yeast extract as nitrogen source for growth.The optimal ZEN degradation temperature,pH and inoculation amount of HR-1 were 30℃,7.0-10.0 and 10%,and the degradation rate of 10 mg/L ZEN was higher than 95%after culturing for 18h.The optimum temperature,pH and NaCl concentration of HR-1 were 30℃,pH7.0 and 10 g/L.These strain can use sorbitol,glucose,fructose and peptone as carbon source and can also use yeast extract as nitrogen source for growth.Meanwhile,the strain HR-1 were resistant to kanamycin and chloramphenicol.The optimum ZEN degradation temperature,pH and inoculation amount were 25-40℃,7.0-8.0 and 10%,and it can degrade 10 mg/L ZEN completely in 4 hours.In the third part,the active ZEN degrading substance of HA-1 and HR-1 were preliminarily studied.The results showed that,the cells of HA-1 didn’t have the adsorption effect of zearalenone.The active ZEN degrading substance were induced by zearalenone and existed in the extracellular supernatant.The optimal ZEN induction concentration of HA-1 was 15 mg/L when the inoculation amount was 4%and cultured at 30℃,180 r/min.In M9 medium,10 mg/L ZEN induces the highest degradation active substances by culturing HA-1 for 48h.The cells of HR-1 couldn’t absorb zearalenone,and the active degrading substance existed in the cells,its’ degradation rate for 10 mg/L zearalenone was 21.2%.In the fourth part,the ability degrading ZEN of HA-1 in the feeds was studied.The results showed that HA-1 could degrade ZEN with different concentrations efficiently in the corn feeds,and the degradation rates of 500-5000 μg/L ZEN were over 90%in 48 h.However,they could hardly degrade ZEN in DDGS feeds.