| Omethoate is a kind of organophosphorus pesticides which is widely used for insects control in agriculture at present in our country. However, their widespread use and toxicity has caused severe environmental pollution, affected the ecological balance and endangered human health. So it is very important to find a good way to ravel out the contamination from omethoate and other organophosphorus pesticides. Biodegradation, especial the degradation of organophosphorus pesticides by microorganism, is thought as a promising way because of its excellences such as simple operation, less cost than physical and chemical approach and good effect.In this research, 18 strains with omethoate-degradation capacity, of which 12 bacterial species and 6 fungal species, were isolated through enrichment culture, isolation and purification from the activated sludge of the waste water treatment station and soil polluted by omethoate of a pesticide factory. Fungal strain YF-3 utilizing omethoate methoate as the sole carbon and energy and bacterial strain YB-10 degrading omethoate by co-metabolism of 18 strains with high degradation rate within 5 days was 68.34% and 73.81%, respectively, were screened by determination of degradation rate. Strain YF-3 and strain YB-10 were tentatively identified as a member of the genera Aspergillus sp. and Bacillus sp., respectively, by means of a series of tests.The effect of initial concentration of omethoate (200 mg·L-1 to 5000 mg·L-1) and glucose (200 mg·L-1 to 10000mg·L-1) on growth of strain YF-3 and YB-10 was discussed. The optimal concentration of omethoate for its growth were 1000 mg·L-1. And biomass increased when the concentration lower than 1000 mg·L-1 of omethoate as carbon source increased, however, high concentration inhibited growth of strain YF-3. The growth lag period of strain YB-10 was longer when the concentration of omethoate increased. The growth of strain YB-10 was not affected and kept stable with the increase of relatively low concentration range of omethoate (200 mg·L-1 to 1000 mg·L-1). But high concentration omethoate increased toxicity and inhibited the growth of strain YB-10. And growth of strain YF-3 and YB-10 were promoted as concentration of glucose increased.The growth conditions including temperature, pH value and medium volumn of omethoate-degradation strains were studied through shaking bottles experiment. The results showed that the preferable growth conditions of strain YF-3 in mineral media containing 1000 mg·L-1 omethoate as sole canbon were as follows: temperature 35℃, pH value 7.0 and 100 mL medium in 250 mL triangle flask, respectively. And as to strain YB-10 in glucose mineral medium containing 1000 mg·L-1 omethoate and 1500 mg·L-1 glucose, it were temperature 30℃, pH value 7.5 and 100 mL medium in 250 mL triangle flask, respectively. Under optimal growth conditions, strain YF-3 and YB-10 reached maximum of biomass: dry weight of 3.984 mg·mL-1 within in 72h and OD600of 1.097 within in 36h, respectively.The effect of initial concentration of omethoate (200 mg·L-1 to 5000 mg·L-1) and glucose (200 mg·L-1 to 10000mg·L-1), pH value, temperature and medium volumn on degradation of omethoate by strain YF-3 was investigated. As a result, when concentration of omethoate increased in the range of 200 to 5000 mg·L-1, the degradation rate by strain YF-3 declined. The addition of low concentration of glucose promoted the degradation of omethoate. In the experiment of omethoate-degradation conditions of strain YF-3, it was discovered that optimal conditions of omethoate-degradation by strain YF-3 were temperature 35℃, pH value 7.0 and 100 mL medium in 250 mL triangle flask, respectively. Under the optimal degradation conditions, degradation rate for omethoate by strain YF-3 within 5 days was 70.34% from 1000 mg·L-1 to 297 mg·L-1.With the addition of glucose of 300 mg·L-1, the degradation rate reached 72.16%.The kind and concentration of carbon source, nitrogen source and phosphate source of medium of strain YB-10 were determined by single-factor tests. Degradation rate was proportional to the increasing of glucose, ammonium nitrate and potassium di-hydrogen phosphate concentration of to some extent, but a little higher concentration of them would inhibit the degradation. The culture medium components of strain YB-10 were optimized by the center-united experiment design of response surface methodology, which were 1.5 g·L-1 of glucose, 0.5g·L-1 ammonium nitrate,1.0g·L-1 of potassium di-hydrogen phosphate. The optimum content of glucose (1.455 g·L-1), ammonium nitrate (0.535 g·L-1) and potassium di-hydrogen phosphate (0.965 g·L-1) was obtained by the method of quadratic regressive revolution design.The study of the effect of degradation factors including concentration of omethoate, pH value, pH value, the inoculation volume and medium volumn rotational speed by the shaking table on omethoate-degradation rate by strain YB-10 was carried out. The results showed that the optimal degradation conditions for the strain YB-10 were initial pH value of 7.0, temperature of 30℃, the inoculation volume 0.25 mL, rotational speed by the shaking table 150 r·min-1, 100 m L medium in 250 mL triangle flask. Under these conditions, degradation rate for omethoate by strain YB-10 within 5 days was 77.34% from 1000 mg·L-1 to 226 mg·L-1 in the optimal culture medium.
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