Study On Characteristics Of Degradation Of Omethoate By The Aspergillus Niger B₁

Fifteen fungal species,which had the ability to tolerate high concentration of omethoate,were isolated from the actived sludge sampled from the pesticide factory treatment device by enrichment and adaptation culture technique.A special strain B1 with high omethoate-degrading ability fungi was isolated in the further screen,which was identified as Aspergillus niger.The optimal temperature and pH value for the cell growth and degradation of omethoate were 30℃ and 5.5,respectively.The omethate concentration that the Aspergillus niger B1 could endure was up to 4000mg/L.When omethoate was supplied as the sole source of carbon,nitrogen and phosphorus,the growth of the strain B1 and degradation of omethoate were slow.In contrast,the supplemental apply of glucose,saccharose,maltose or glycerol could promote the cell growth and degradation of omethoate markedly.The strain B1 was able to use omethoate as the sole phosphorus source.Addition of inorganic phosphate promoted the growth of the strain B1,and there is no influence on biodegradation activity of the strain B1.When omethoate and glucose coexisted,the isolate Aspergillus niger B1 showed the typical catabolic characteristic to utilizate omethoate and glucose sequentially.In the present of omethoate and glucose,strain B1 used glucose as energy and carbon source for cell growth preferentially.When the concentration of glucose declined to 0.1g/L,omethoate began to degradated by the strain B1 obviously.The data of Fed-Batch experiments showed that the highest specific degradation rate was 0.491mg omethoate/g(dry mass)·h when the concentration of glucose is 0.1-0.3g/L.The optimal ratio of the weight of additional carbon substance to omethoate was 5-20.The significant influence of different concentrations of omethoate on the growth rate of strain B1 and the omethoate degradation rate wasobserved in the experiments.Under the relatively low concentration range of omethoate(40-365mg/L),the increase of concentration of omethoate could promote the cell growth when omethoate provided the sole phosphorus source.The optimal concentrations of omethoate for its degradation were 820-1345mg/L.However the higher concentration of omethoate showed obvious inhibition on the growth of the strain B1 and the degradation of omethoate.GC-MS was used to trace the intermediate metabolite during the degradation of omethoate by strain B1,and reported the the degradative pathway and the intermediate metabolite in the degradation of omethoate by strain B1 for the first time.No obvious intermediate metabolites were detected except O,O,S-Trimethyl Phosphorothioate(TMP).The GC-MS analysis of the sample with different degradation rate showed that the consumption rate of TMP was high by Aspergillus niger B1,and no accumulations of TEP were observed in the omethoate biodegradation process. The results demonstrated that Aspergillus niger B1 could degradate and mineralize omethoate and a safe degradation could be hoped.A model test of biomediation of omethoate contaminated soil by strain B1 was carried out.the experimental results showed that Aspergillus niger B1 was able to degradate omthoate well in the soil,and the degradation rate was promoted markedly when Aspergillus niger B1 cooperated with autochthonal microorganisms in the soil.When the concentration of omethoate were 150-500mg/kg(dry soil), the highest omethoat degradation rate by the strain B1 was achieved.The experimental results ,including the isolation of the special strain with high omethoate degradation activity,the study of the cometabolism characteristics of Aspergillus niger B1,the kinetics of omethoate degradation and the modeled test of biomediation for the contaminated soil by strain B1 showed that Aspergillus niger B1 possesses a potential application value for the of bioremediation of omethoate contaminated wastewater or soil on the large scale.