Optimization of growth media for maximal production of insecticidal vegetative protein (vip3A) from Bacillus thuringiensis and its activity against black cutworm (Agrotis ipsilon)

Bacillus thuringiensis is a Gram-positive bacterium naturally found in soil, water and grain dust. B. thuringiensis has been used for decades as biological control for pests of economical and medical importance. The aim of this study was to test different growth media for the optimal production of vegetative insecticidal protein (Vip3) by B. thuringiensis recovered from the local environment. The local B. thuringiensis was grown under shaker conditions in commercially based media and commonly known growth based media to produce Vip3. The optimal C/N ratio for Vip3 production (3.88) was achieved with 20 g/l of glucose as carbon source and 15 g/l of soybean as nitrogen source. Different combinations of carbon and nitrogen sources were examined. Glucose and soybean were the best carbon and nitrogen source, respectively, for maximal Vip3 production. Terrific Broth supplemented with 20 g/l glucose was found to yield optimum growth significantly (P <0.01, t-test) after 12, 14, 16, 18 and 20 h compared to a formulated medium with optimized C/N ratio of 3.88. The highest vegetative cell count was achieved after 22 h, thus indicating a higher production of Vip3 protein. The method described in this study will facilitate the production of biopesticides in a cost-effective manner.   Key words: Bacillus thuringiensis, bioinsecticides, Vip3, culture media, vegetative protein.