Improvement of the Production of Entomopathogenic Proteases of Bacillus thuringiensis. K. Ennouri, R. Ben Ayed, H. Ben Hassen, H. Azzouz, and M.A. Triki. (Tunisia)

Abstract

Bacillus thuringiensis (Bt) is a spore forming bacterium that produces an insecticidal crystalline protein (ICP) making it a successful biopesticide. The ICPs are also referred to as Cry proteins and contain delta-endotoxins which cause mortality of insects belonging to different orders such as Diptera, Coleoptera and Lepidoptera. Bt subspecies produce also proteases which affect their entomotoxicity toward targeted insects as proteolytic activities are strongly associated with Bt crystal protein. Statistical techniques were applied to optimize the fermentation medium composition for the production of bacterial proteases in shake-flask cultures. An experimental statistical design was performed to evaluate the effects of different components on the concentration of proteolytic enzymes. Preliminary results showed that starch and K2HPO4 are able to increase Bacillus sp. protease production. In order to obtain more accurate results, interactions between ingredients were also studied. In concordance with coefficient of determination (R²) value, considered as the most important criterion for predictive model success, the best model demonstrated the effect of interactions and allowed precise prediction of protease production. In fact, K2HPO4, KH2PO4, MgSO4, FeSO4 as well as Soybean meal × starch and MnSO4 × starch interactions were shown to have active action on protease production. This method revealed that limited number of experiments allowed useful results.

Keywords

• Bacillus thuringiensis
• coefficient of determination
• production
• protease
• statistical design