Degradation Characteristics Of AFB1 And OTA By Stenotrophomonas Sp.CW117 And The Preliminary Molecular Mechanisms

Mycotoxins are secondary metabolites produced by molds,which are highly hazardous,widely distributed in agro-products,processed food and feed,and the chemical structures were quite stable.Once contaminated in agro-products of foods,they could stably exist in the environment and are difficult to degradated naturally.Among them,aflatoxin B1and ochratoxin A are the two most dangerous and widely distributed mycotoxins in the food and animal feeds.The biodetoxification method is currently considered as a safe and effecient method.The microbiological mechanism of detoxification has become the research hotspot in this area.In this study,a di-functional strain Stenotrophomonas sp.CW117 which showed degradation abilities to AFB1 and OTA was selected and the preliminary degradation mechanisms were investigated.The AFB1 and OTA were rapidly degraded by strain CW117 within a short time under the low concentration of 40?g/L.To be specific,at the concentration of 40?g/L for each mycotoxin,OTA was completely degraded after 60hours incubation and AFB1 was completely degraded after 96 hours incubation by inoculated with single colonies of strain CW117.In this study,the cell-free supernatant,cells pellet suspension and cell lysate were tested for AFB1 and OTA degradation,respectively.The investigation results showed that the degradation activity to AFB1 and OTA are existed in cell-free supernatant and cell pellet,respectively.The optimum temperature for OTA degradation by strain CW117was between 20?-40? and the optimum p H was about 7-8.The AFB1 degradation efficient of strain CW117 was increased gradually with the increasing of incubation temperature.The optimum temperature is 90?and the optimum p H for AFB1degradation was at the neutral conditions.The additive metal ions of Cu²⁺,Ca²⁺,and Zn²⁺significant inhibited the degradation abilities to OTA and AFB1.The additives of EDTA,EGTA and proteinase K at 35? for 6 h resulted in a significant decrease of the OTA degradation ratios.Pretreatment of cell lysate with SDS or 100? boiling,the degradation capacity to OTA was disappeared.The preliminary results of the degradation mechanism indicated that the strain CW117 degrading OTA by intracellular enzyme(or enzymes).Compare to OTA degradation,the pretreatment of100? boiling or proteinase K to cell-free supernatant(the active content to AFB1)showed no(or very limited)influence to AFB1 degradation.Pretreatment of EDTA or EGTA or SDS to cell-free supernatant also showed significant inhibition to AFB1degradation.The cloning,heterologous expression and degradation activity of the laccase obtained form the genome of CW117 was further evaluated.It was found that the laccase from CW117 also showed degradation AFB1 ability,but laccase should be sensitive to high temperature and proteinase K.The results of this study indicated that the AFB1degradation mechanism of CW117 should be the non-specific oxidative degradation by oxidizing substances(possibly including extracellular laccase and inorganic oxides)in the bacterial culture supernatant.