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Diversity of Bacillus thuringiensis environmental isolates showing larvicidal activity specific for mosquitoes
1Institute of Biological Control, Faculty of Agriculture, Kyushu University, Fukuoka, Japan.
Abstract:
Seven mosquito-specific strains of Bacillus thuringiensis isolated in Japan were examined for their flagellar (H) antigenicities and the properties of parasporal inclusion proteins. They were assigned to six H serovars: serovar fukuokaensis (H 3ade); serovar canadensis (H 5ac); serovar darmstadiensis (H 10); serovar kyushuensis (H 11ac); serovar shandongiensis (H 22); and an undescribed serovar belonging to H serotype 20. Purified parasporal inclusions exhibited moderate mosquito larvicidal activities with LC50 values ranging from 1 microgram ml-1 to 10 micrograms ml-1. The inclusions of these strains consisted of highly heterogeneous multiple protein components, and five distinct patterns were evident in their SDS-PAGE profiles. Antibodies against kyushuensis inclusion proteins were reactive with all strains to varying degrees, while israelensis antibodies gave only relatively weak reactions with the seven strains. Similarity in antibody-binding profiles was associated with similarity in SDS-PAGE profiles. In a given strain, different antisera gave altered immunoblot profiles. Haemolytic activity was shown by solubilized parasporal inclusion proteins of five of the seven strains.
Insights
Seven Bacillus thuringiensis strains showed moderate mosquito larvicidal activity. Their flagellar antigens and inclusion proteins were analyzed, revealing distinct serovars and protein profiles with varying larvicidal efficacy.
Area of Science:
- Microbiology
- Insect Pathology
- Biochemistry
Background:
- Bacillus thuringiensis (Bt) is a bacterium known for producing insecticidal toxins.
- Mosquito control is a significant public health concern, necessitating effective biological control agents.
- Understanding the diversity and properties of Bt strains is crucial for developing targeted biocontrol strategies.
Purpose of the Study:
- To characterize seven mosquito-specific Bacillus thuringiensis strains isolated in Japan.
- To investigate their flagellar (H) antigenicities and parasporal inclusion proteins.
- To assess the larvicidal activity and protein composition of these Bt strains against mosquito larvae.
Main Methods:
- Serological analysis of flagellar antigens to determine H serovars.
- SDS-PAGE to analyze the protein composition of parasporal inclusions.
- Larvicidal bioassays to determine LC50 values against mosquito larvae.
- Immunoblotting using specific antisera to assess protein cross-reactivity.
Main Results:
- Seven strains were assigned to six H serovars, including an undescribed serovar within H serotype 20.
- Parasporal inclusions showed moderate mosquito larvicidal activity (LC50: 1-10 µg/mL).
- SDS-PAGE revealed five distinct protein profiles, indicating heterogeneous inclusion proteins. Cross-reactivity of inclusion proteins varied among strains, correlating with SDS-PAGE similarity.
- Haemolytic activity was observed in five of the seven strains' solubilized inclusion proteins.
Conclusions:
- The characterized Bacillus thuringiensis strains represent a diverse group with potential for mosquito biological control.
- Variations in flagellar antigens and parasporal inclusion proteins influence their efficacy and cross-reactivity.
- Further research into these strains could lead to the development of novel, targeted mosquito larvicides.