CHARACTERIZATION OF MOSQUITO-SPECIFIC BACILLUS-THURINGIENSIS STRAINS COISOLATED FROM A SOIL POPULATION

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.