Delta-endotoxin production and toxicity enhancement by using vegetable oils as oxygen vectors

Delta-endotoxins are produced by Bacillus thuringiensis (Bt) and have their main application in agriculture to manage insect crops and as antimicrobial. Its large scale production is limited by oxygen availability during Bt fermentation since delta-endotoxin synthesis requires high oxygen level. Therefore, it requires the enhancement of the agitation speed and air flow rate, which could be solved by adding an oxygen vector. So, the objective was to evaluate the use of oxygen vectors (soybean, corn and sunflower oil) on the enhancement of delta-endotoxin production and its toxicity against Spodoptera frugiperda and pathogenic microorganisms. In this way, the effects of oils on fermentation were studied from a 2⁴ full experimental design, where their concentration varied from 0% to 3%. Posteriorly, the best oil and concentration to produce delta-endotoxin was studied in a 7.5 L agitated tank bioreactor. The experimental design revealed that corn oil (3%) and sunflower oil (3%) could significantly enhance delta-endotoxin production, and this combination was considered the best condition to produce delta-endotoxins. In addition, kinetics parameters like X_m, P_x, µ_X.max and µ_S.max were increased in comparison to a fermentation without oxygen vector. Delta-endotoxins produced in the presence of oils showed higher activity against S. frugiperda and bacteria isolated from goat mastitis. Therefore, this research demonstrates that corn and sunflower oils can serve as oxygen vectors, enhancing both the production of delta-endotoxins and their toxicity against pathogenic bacteria and Lepidopterans.