| Bacillus thuringiensis (Bt) was one of the most widely used microbial insecticides in the world. The studies on approaches to increase the insecticidal efficacy of Bt have been hot spots recently. Biomagnetism is widely applied in agriculture, medicine and microbial fermentation etc. The influence of magnetic field on the bioactivity of microorganism is one of the key researchs. The infuence of magnetic field to the growth and toxicity of the Bt G-02 strain and Bt HD-1 strain in the paper were studied. The arm is order to find out the parameters of magnetic field which could increase the yield of fermentation and toxicity of Bt.Bt G-02 and Bt HD-1 were cultured in the broth with the magnetic treated water respectively. The results indicated that The sporulation of G-02 and HD-1 strains were effected by the water treated using different magnetic intensity and different time. The sporulation of G-02 strain was improved in the water treated using the 28~50Gs magnetic intensity, and the maximum capacity of sporulation was up to 6.1×108 spore/mL in the 43Gs treated water, which increased 11% compared with control. The sporulation of HD-1 strain was improved in the water treated using 7~43Gs magnetic intensity, and the maximum capacity of sporulation was up to 6×108 spore/mL in the broth with 14Gs treated water, which was 28% higher than control. The sporulation capacity of G-02 and HD-1 were also improved in the 43Gs 2~12h treated water and the 14Gs 2~14h treated water respectively.The growth and sporulation of G-02 and HD-1 strains during the fermentation were effected directly by different magnetic intensity, different pulse width and different treated time. In constant magnetic field, the sporulation of G-02 strain was improved by the 43~50Gs magnetic intensity, the maximum capacity of sporulation increased 26% compared to control by treatment of 43Gs magnetic intensity, furthermore, the treatment of 14~26h 43Gs magnetic intensity made the sporulation capacity of G-02 increasing 23% compared with control. The sporulation capacity of HD-1 strain was improved by the 7~36Gs magnetic intensity, the capacity of sporulation was up to maximum which incresed 100% compared with control in 14Gs treatment, furthermore, it was 108% higher than control in treatment of 14~26h 43Gs magnetic intensity. The 4~7ms pulsed magnetic field also improved the sporulation capacity of G-02 strain during the fermentation. 5ms pulsed width magnetic field made the sporulation capacity of G-02 to the maximum that was 38% higher than control, and the sporulation capacity of G-02 increased 23% compared with control after treatment of 0~14h pulsed width 5ms magnetic field. the sporulation of HD-1 strain during the fermentation was improved directly by the 1~5ms pulse width magnetic field. In pulsed width 1ms magnetic field, the sporulation capacity of HD-1 was up to the maximum that increased 22% compared with control, furthermore the sporulation capacity of HD-1 increased 57% compared with control in 28~48h pulsed width 5ms magnetic field.The cry gene identification using PCR-PFLP showed that G-02 also had cry1Aa,cry1Ab,cry1Ac and cry2 Ab gene like HD-1. The two Bt strains all had insecticidal activities to some Lepidoptera pests. The insecticidal activities of the magnetic fermentation productes from G-02 and HD-1 strains on Helicoverpa armigera were assayed. The result showed that the insecticidal toxicity of G-02 strain was improved after treatment using the 43~50Gs magnetic intensity and the 4~7ms pulse width magnetic field. 43Gs magnetic intensity made the toxicity synergism ratio of G-02 to H. armigera larvae to maximum that increased 26% compared with control, and the toxicity was 6% higher than control after treatment 14~26h 43Gs magnetic intensity, 5ms pulse width magnetic field made the toxicity synergism ratio of G-02 to H. armigera to maximum that increased 23% compared with control, and the toxicity was 9% higher than control in 0~14h 5ms pulse width magnetic field; the insecticidal toxicity of HD-1 strain was improved after treatment using the 7~28Gs magnetic intensity and the 1~4ms pulse width magnetic field. 14Gs magnetic intensity made the toxicity synergism ratio of G-02 to H. armigera larvae to maximum that increased 25% compared with control, and the toxicity was 8% higher than control after treatment 14~26h 14Gs magnetic intensity, 1ms pulse width magnetic field made the toxicity synergism ratio of G-02 to H. armigera to maximum that increased 18% compared with control, and the toxicity was 12% higher than control in 0~14h 1ms pulse width magnetic field. |
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