Studies Of The Behavior And Ecological Effect Of Bacillus Thuringiensis And Bacillius Amyloliquefaciens Within Phyllosphere

Microbial pesticide is an ideal substitute for chemical pesticide in agricultural ecosystem. Generally, microbial pesticide is believed environmental safe because it derives from the nature and is released to nature. However, it is uncertiain if the microbial pesticide is stressful for the other microorganisms? How severe effects it may have on the other living organisms? Does it have potential ecological safety risk? All these issues are required to address. it may have when it is applied to control pests in the natural evironments. There is no unanimous conclusion about these scientific questions. Moreover, there is also no systematic study and assessment. Therefore, Bacillus thuringiensis (Bt) and Bacillus amyloliquefaciens (Ba) were used to study there dynamic behavior and effect on microbial community structure within phyllosphere and mice intestinal. This study supplies a theoretical basis and technical support for the development of environmental safety assessment guideline of microbial pesticides and establishment of detection method.With aid of antibiotic labeled strain, we have monitored the dynamic of Bt within phyllosphere of cotton, amaranth and rice after the leaves are sprayed with Bt at recommended dose of 1.5×107cfu/mL and high dose of 1.5×109 cfu/mL. Results showed that the dynamic of Bt within phyllosphere was both dose and plant species dependent. At the recommended dose, the dynamic treat of Bt on the given three plant leaves are similar and maintain a stable population of (6.3×103 cfu/g) at 15 days after inoculation, however, at high dose, the Bt abundance within cotton phyllosphere declines much faster that it within the phyllosphere of amaranth and rice. According to the cell count of the microorganisms, Bt doesn’t significantly influence the bacterial and fungal population within the given three plants. Moreover, Bt dose show great impact on the bacterial community structure within cotton phyllosphere when the Bt was sprayed at high dose based on PCR-DGGE and 16S rRNA sequence analysis. Compared to the negative control, Acinetobacter sp., Sporosarcina sp., Bacillus sp., Pseudomonas sp., Paenibacillus sp. cannot be detected at 7 d after Bt treatment. However, Bt also alters the bacterial community within amaranth phyllosphere only at the recommended Bt dose, Pseudomonas sp., Yersinia sp., Sporosarcina sp., Bacillus sp., Streptoplyta sp. have not been monitored on the Bt treatment. Furthermore, Bt has not any impacts on the bacterial community composition within rice phyllosphere as well as fungal communities within all the given three plants.With the same methods mentioned above, we have determined the dynamics of Bt and its effect on both the population size of three physiologically important bacteria and bacterial communities within mouse gut. According to a series counting of the cell numbers of Bt, we have detected Bt in the mouse gut at 6h and 12h, but not at 24h after gavaging Bt at 1.2×108 cfu/mL,0.4 mL/capital for 3 times. Moreover, Bt does not show any impacts on the community structure and size of three dominant species such as Escherichia coli, Bifidobacterium spp. and Lactobacillus spp. in the gut of mouse based on plate counting method and PCR-DGGE analysis. These results suggest that Bt has no influence on the ecological environments of mouse gut and is environmental safe.With rifampicin labeled strain, we have monitored the dynamic of entophytic bacteria Ba within phyllosphere of cotton, amaranth and rice after the leaves are sprayed with Ba at recommended dose of 1.5×l07cfu/mL. Results showed that the dynamics of Ba within phyllosphere of the given three plant phyllosphere were similar and maintain a stable population of (8.3×103 cfu/g) at 15 days after inoculation. According to the cell count of the microorganisms, Bt doesn’t significantly influence the bacterial and fungal population within the given three plants. These results indicate that endophytic bacteria Ba is a kind of safety biocontrol strain.According to leaves’ enzymatic analysis using guaiacol, potassium permanganate titration and Tetrazolium methods, Bt and Ba do not have effects on the activities of peroxidase, catalase, superoxide dismutase at dosage of 1.5×107 cfu/mL. In addition, these two biocontrol agents do not influence the chemical constituents of cotton leaves based on GC/MS analysis. These results indicated that Bt and Ba are safe for the targeted plants.