Characterization and biological activity of a Brazilian isolate of Bacillus sphaericus (Neide) highly toxic to mosquito larvae

ABSTRACT

Primary powders of Bacillus spharicus strain S2 isolated from soil samples in Brazil, and strain 2362 were produced in a 14 liter fermentor. Growth patterns and sporulation observed in three trials with strains S2 and 2362 in the fermentor were similar. Second-instar larvae of Culex quinquefasciatus, Anopheles albimanus, Anophles quadrimaculatus and Aedes aegypti exposed for 48 hr to strain S2 responded with LC50 values of 0.25, 5.95, 12.28 and 140.0 ppb of lyophilized primary powder, respectively. Under the same conditions, strain 2362 resulted in LC50 values of 0.39, 7.16, 16.93 and 307.0 ppb of lyophilized primary powder, respectively, in those mosquito larvae. Statistical analysis of the bioassay data did not show significant differences among LC50 values observed in B. sphaericus strains S2 and 2362, at the 0.05 level. Toxins of strains S2 and 2362 were extracted at pH 12 with NaOH. Electrophoresis of the extraxts in plyacrylamide gel under denaturing conditions reveled the 51 and 42 kDa toxins in both S2 and 2362 B. Sphaericus strains. The presence of the 42 Da peptide in the extracts was confirmed by Western blot and Elisa, with anti-42 kDa IgG previously prepared from strain 2362.