Vegetative insecticidal protein (Vip3A) production by Bacillus thuringiensis Bt294 and its efficacy against Lepidopteran pests (Spodoptera exigua)

A vegetative insecticidal protein, Vip3A, is highly active against lepidopteran pests, which are the most important pests in most tropical countries. An important aspect of the successful commercial production of this bacterial insecticide is the development of bacterial culture media that maximize the titres of this protein and cost reduction. This study aimed to investigate and optimize Vip3A production by Bacillus thuringiensis Bt294 using statistical methods and 3-step sequential approaches. The experimental design showed that the production of Vip3A was maximized to 300 mg/L when the bacterium was cultivated in medium composed of 5.05 g/L glycerol, 49.17 g/L soytone, 30.05 g/L casein hydrolysate, 1.99 g/L CaCl₂.2H₂O, 7.5 mg/L CuSO4, 15 mg/L MnSO₄.H₂O, 9.4 g/L K₂HPO₄, 2.2 g/L KH₂PO₄, 0.2 g/L MgSO₄.7H₂O, 5 g/L yeast extract, 2.5 mg/L NiCl₂.6H2O and 3 mL/L vitamin solution. B. thuringiensis Bt294 Vip3A toxin was highly toxic to Spodoptera exigua with LC50 values of 187.1 ng/cm² at 7 days. This result demonstrated that a high titre of Vip3A produced by B. thuringiensis Bt294 will be useful as a biological control agent. This optimization will allow production to be scaled up for commercial production in the future.