Effect of the growth rate of Bacillus thuringiensis in the cry protein production and their toxicity against S. frugiperda

This paper presents the effect of the growth rate of Bacillus thuringiensis HD-1 (Bt-HD1) in the Cry1Ac and Cry2Ab protein production and their level of toxicity against S. frugiperda. Production of Bt-HD1 was performed in fed batch (30 ° C, pH 7 and minimum oxygen concentration of 21%) with variation in the total solid concentration (CST) in the feed stream. The CST was set in the range 10g/L - 150 g/L, and was composed of glucose, yeast extract, defatted soy flour and corn solids, which were added at a carbon:nitrogen ratio of 7. We analyzed microbial growth, spore production and the Cry protein production, and it was found that there is a relationship between the growth rate of Bt-DH1 and the next two parameters: Cry1Aa/Cry2ab protein ratio and the toxicity of Cry proteins against S. frugiperda. The combination of proteins produced by Bt-HD1 is known for its high toxicity. However, the study shows that this can be varied in order to obtain a desired toxicity for a specific application.