The Study Of Detoxification Of Ochratoxin A By Acinetobacter Sp. BD189

Ochratoxin A (OTA) is a secondary metabolite produced by some fungal species of the genera Aspergillus and Penicillium. OTA affects agricultural products all over the world and causes harmful effects on animal and human health because of its highly toxic properties.In this paper, we successfully identified a bacterial isolate which had capability to detoxify OTA. Then we conducted a research on the detoxifying capability and detoxifying characteristics of the bacterial isolate.This study could be divided into three parts. The first part was screening for microorganisms which had capability to detoxify OTA. One of the bacterial isolates exhibited detoxifying capability. After sequencing and analyzing its 16S rDNA, this isolate was identified as Acinetobacter sp. The isolate was named as Acinetobacter sp. BD189 by our lab.In the second part, the detoxifying capability and possible detoxifying mechanisms were investigated and a micronucleus assay was conducted to provide biological proof of the detoxifying capability of Strain BD189. After 24 h of incubation with OTA, the viable bacteria of Strain BD189 exhibited strong detoxifying capability (removed more than 80% of OTA) while the heat-inactivated bacteria could not remove OTA. In addition, HPLC detected the presence of the degradation product Ochratoxinα(OTα) after the viable bacteria incubated with OTA. This indicated that the detoxification mechanism of OTA by Acinetobacter sp. BD189 was a biodegradation process rather than a cell-wall adsorption. The results of micronucleus assay showed that the pretreatment of Strain BD189 with OTA could cause a substantial decrease of micronucleus formation induced by OTA in HepG2 cells. This indicated that Strain BD189 could degrade OTA and really decreased the biological toxicity of OTA.The third part was to investigate the detoxifying characteristics of Acinetobacter sp. BD189 and the properties of its OTA-degrading enzyme. The time curve of OTA degradation by Strain BD189 was accordant with the characteristics of enzymatic reaction. OTA degradation rate reached highest between 30 and 40℃while it was much lower at 10,20and 50℃. When the effect of pH was examined, maximum degradation was observed at pH 6.5 and pH 7.5 while it was much lower at acidic and alkaline conditions. Moreover, the higher the concentration of bacteria was, the more OTA was degraded. The results showed that the OTA-degrading enzyme of Strain BD189 was an endoenzyme, and its optimum temperature and pH for degrading activity were 30℃and pH8.0, respectively. The metal-ion chelator EDTA could inhibit the degrading activity of the enzyme while the Carboxypeptidase Inhibitor could not. This suggested that the enzyme was a metalloenzyme and had different properties compared to carboxypeptidase A, which was another enzyme that could degrade OTA to OTα.Conclusively, Acinetobacter sp. BD189 had significantly detoxifying capability of OTA and its efficiency was high under mild conditions. Acinetobacter sp. BD189 and its degrading enzyme can provide new options for the study of OTA biological detoxification.