Antibacterial Mechanism And Control Effect To The Silkworm Disease Of An Antagonistic Endophytic Burkholderia Cepacia Lu10-1 Isolated From Mulberry

The bacteriosis and fungous disease of silkworm caused heavy economic losses every year. The drugs in hand have better control efficiency, but they have some disadvantages, for instance long-term using could reinforced drug resistance of pathogenic bacteria; impacted on the environment; some drugs had harmful to human body. To overcome the limiting problems of the drugs, developing new type microbial preparation as silkworm drugs is a key research direction.Burkholderia cepacia Lu10-1 is an antagonistic bacteria, isolated from the mulberry leaves, it was had strong antagonistic activity to the pathogenic bacteria of many animals and plants, for instance Colletotrichum morifolium, Septogloeum mori, Dothiorella gregaria, Staphylococcus aureus and Bacillus thuringis, and the strain Lu10-1 could stably colonize in the mulberry body, has a bright future.This research through modality observation and pharmacological experimental methods, analyzed its antagonistic activity to the Bacillus bombysepticus and Beauveria bassiana of silkworm, and the control efficiency of the supernatant of strain Lu10-1 zymotic fluid to septicemia and white muscardine, and investigated the effect of the physiological functions and the cocoon quality of silkworm by the supernatant. The main results were showed as the followings.1 We measured the inhibitory effect, minimal inhibitory concentration (MIC), and minimal bacteriocidal concentration(MBC) of antibacterial crude extract to the Bacillus bombysepticus. The results indicated that the antibacterial crude extract had strong antagonistic activity against the Bacillus bombysepticus. Its diameter of inhibition zone reached 18.20 mm. The MIC and MBC of antibacterial crude extract were 1.56 mg/mL and 3.13 mg/mL.2 Using spectrophotometric method, conductimetric method, and SDS- PAGE method measured the effect of the antibacterial crude extract to the growth, extracellular conductivity, intracellular and extracellular saccharide and proteins of the Bacillus bombysepticus. The results showed that after being treated by antibacterial crude extract, the Bacillus bombysepticus never appeared logarithmic phase, cell membrane permeability had changed, intracellular saccharide and protein leaked from the cell, macromolecular protein of intracellular degraded.3 The modality failure of the Bacillus bombysepticus cell was observed by electron microscope. The results showed that the antibacterial crude extract of strain Lu10-1 made the modality of the Bacillus bombysepticus damaged, inner substance outflowed, formed cavity and ablation of the cells. That just shows the antibacterial crude extract of strain Lu10-1 has apparent inhibitory effect to the Bacillus bombysepticus by destroying its cell wall and membrane.4 We measured the inhibitory effect of the antibacterial crude extract of strain Lu10-1 to the spore germination and growth of Beauveria bassiana. The results showed that the antibacterial crude extract had strong antagonistic activity against the Beauveria bassiana. Its diameter of inhibition zone reached 17.00 mm; and its also inhibit the growth and spore germination of Beauveria bassiana.5 The modality failure of the Beauveria bassiana cell was observed by electron microscope. The observation of optical microscope indicated after being treated with the antibacterial crude extract, the spore of Beauveria bassiana became collective and had such abnormalities as uneven distribution of cellular contents, deformation of spores, disappear of cellular contents and disrupted cellwall; and the mycelia of Beauveria bassiana became thicker, retorted, corrugated, and inflated with inner substance outflowed and ablation of the cells. The observation of electron microscope indicated the antibacterial crude extract could make the spore and mycelia of cytoplasm concentrated, plasmolysis, cellwall became attenuation, damaged, inner substance outflowed and formed cavity. That just shows the antibacterial crude extract has apparent inhibitory effect to the Beauveria bassiana by destroying its cell wall and membrane.6 We measured the control effect of the supernatant of strain Lu10-1 zymotic fluid to the septicemia and white muscardine of silkworm, and the effect of the physiological functions and the cocoon quality of silkworm. The results showed the supernatant of strain Lu10-1 had better control effect to the septicemia and white muscardine of silkworm, the supernatant of strain Lu10-1 achieved 41.19% control efficiency and 24.00% prophylactic effect on silkworm septicemia respectively; the prophylactic and treatment effective rate of supernatant to white muscardine respectively reached 55.88% and 34.00%; while no harmful effect was observed on the physiological functions and cocoon quality of the silkworm.