The Study Of Detoxification Of Ochratoxin A By Bacteria

Ochratoxin A (OTA) is a secondary metabolite produced by some fungal species of Aspergillus and Penicillium. OTA can be commonly found in grain and agricultural products as a significant contaminant and it causes harmful effects on animal and human health because of its highly toxic properties.In this paper, we successfully identified three bacterial strains which had the ability of detoxifying OTA, and their capability and characteristics of OTA detoxification were studied.This study could be divided into three parts. The first part was screening for microorganisms which had ability to detoxify OTA. Three bacterial strains were screened out from soil, two of them were indentified as Bacillus and one was Rhizobium. They were respectively named Bacillus sp. YB139, Bacillus sp. YB140 and Rhizobium sp. GL331.In the second part, The capability and mechanisms of three strains above and Acinetobacter sp. BD189 that we had already got before were studied. Acinetobacter sp. BD189 showed the highest OTA detoxification rate 63.9% after 24h compared with other three bacterial strains Bacillus sp. YB139(48.2%), Bacillus sp. YB140(43.4%) and Rhizobium sp. GL331(25.1%). After incubation with OTA, the viable bacteria of these strains exhibited effective OTA detoxification while the heat-inactivated bacteria could not remove OTA. In addition, HPLC detected the presence of degradation product Ochratoxinα(OTα) after treatment by viable bacteria. This indicated that the mechanism of OTA detoxification by these strains was a biodegradation process rather than adsorption by cell wall. Furthermore, the cell lysate could degrade OTA while the supernatant of bacterial culture solution could not, which indicated that the OTA-degrading enzymes of these strains were endoenzymes.The third part was to investigate the characteristics of OTA detoxification by the above strains. The higher the cell concentration was, the more OTA degraded, and the kinetics curve was accordant with that of enzymatic reaction. BD189 and YB140 showed highest OTA degradation at 40℃w hile 30℃for YB139 and GL331. When the effect of pH was tested, highest degradation of BD189 was observed at pH6.5 and pH7.5 while the optimal pH was 5.5 for GL331. YB139 and YB140 showed strongest ability to degrade OTA at pH4.5 and pH5.5. Besides, the metal ion chelator EDTA could inhibit the activity of these strains for OTA biodegradation while the carboxypeptidase inhibitor from potatoes could not. This suggested that the enzymes from these strains belonged to another type of metalloenzymes which could degrade OTA to Otαbut were not carboxypeptidases, which have been reported.