Production of asporogenous mutants of Bacillus sphaericus 2362 in continuous culture

Aims: To report the production of asporogenous mutants (Spo(-)) of Bacillus sphaericus 2362 in continuous culture. Methods and Results: Microbial culture samples were taken at 0.05 h(-1) dil ution rate and plated out on nutrient agar plates. Translucent colonies wer e obtained with vegetative morphology under phase contrast microscope. Heat resistance evaluations at different temperature settings showed that the S po(-) mutants had lower heat resistance than the Spo(+) wild type. Western blots analyses carried out on both wild type and the mutants indicated the presence of binary protein toxins of 42 and 51 kDa in both. Bioassays carri ed out on the wild type and the Spo(-) mutants against mosquitoes showed th e mutants to be 100-fold less toxic in comparison to the wild type. Conclusions: Existence and production of asporogenous mutants of Bacillus s phaericus 2362 in continuous culture at low dilution rates is demonstrated by this study. The organism's ability to produce toxins appears to be signi ficantly reduced by the mutational process. Significance and Impact of the Study: The production of asporogenous mutant s had not been reported previously among strains of Bacillus sphaericus. Th e present report on the toxigenic capability of asporogenous mutants also r aises the possibility of using continuous culture to significantly improve the productivity of toxin production in future.