Characterization of Mosquito-Specific Bacillus thuringiensis Strains Coisolated from a Soil Population

Abstract

Summary Ten isolates of Bacillus thuringiensis , coisolated from a single soil sample, were assigned to the three flagellar (H) antigenic serogroups: one isolate was identified as serovar kyushuensis (H antigen 11a:11c), six were referable to serovar amagiensis (H antigen 29), and the others belonged to a previously undescribed serovar. These ten isolates produced similar spherical to irregular-shaped parasporal inclusions. In oral toxicity tests, they all exhibited moderate larvicidal activity to the mosquitoes, Aedes aegypti and Culex pipiens pallens , but not to the silkworm, Bombyx mori , and the fall webworm, Hyphantria cunea . SDS-PAGE analysis revealed that the parasporal inclusions of these isolates consisted of polypeptides of 25–28, 70–80, and 140–150 kDa, showing a high similarity in protein profiles between ten isolates and the type strain of serovar kyushuensis . Strong immunological relationships were evident among inclusion proteins of these isolates and the type strain of kyushuensis , when examined by immunodiffusion and immunoblotting tests with polyclonal antibodies raised against the whole parasporal inclusion proteins. The results indicate that these B. thuringiensis isolates from a single soil microhabitat produce closely related mosquito-specific toxins, although they belong to three different H serogroups.