Optimization of bioinsecticides overproduction by Bacillus thuringiensis subsp. kurstaki using linear regression

A multiple linear regression analyses were performed to screen for the significant factors simultaneously influencing production of delta-endotoxin, proteolytic activities and spore formation by a Bacillus thuringiensis kurstaki strain. Investigated factors included: pH of the medium, available oxygen and inoculum size. It was observed that oxygen availability was the most influencing setting on both deltaendotoxins production and spores counts, followed by initial pH of the medium and inoculum size. On other hand, pH of medium was found to be the most significant parameter for proteolytic activity, followed by inoculum size and dissolved oxygen. Our results suggested that the first order with two-factor interaction model seemed to be more satisfactory than simple first order model for optimization of delta-endotoxin overproduction. The coefficients of determination (R²) indicated a better adequacy of the second order models to justify the obtained data. Based on results, relationships between delta-endotoxins production, proteolytic activities and spores counts were established. Our results can help to balance delta-endotoxins production and its stability.