Carboxy-terminal half of Cry1C can help vegetative insecticidal protein to form inclusion bodies in the mother cell of Bacillus thuringiensis

Vegetative insecticidal protein (VIP) is a class of insecticidal proteins produced by some strains of Bacillus thuringiensis during the vegetative stage of their growth and has toxicity against a wide spectrum of lepidopteran insects. Unlike insecticidal crystal proteins, which are produced as parasporal crystal proteins within the cell during sporulation, VIP is secreted into the culture medium. Here, we show that Vip3Aa7 protein can be relocated into the mother cell of B. thuringiensis by altering its synthesis using cry1C promoters, combined with a cry1C transcription termination sequence at the 3′ region and a STAB-SD sequence from cry1C promoters at the 5′ region of the gene. Further, when the carboxy-terminal half of Cry1C was included in the construct, the synthesis of Vip3Aa7 markedly increased, and its expression was relocated into the mother cell in the form of inclusion bodies. The expression of Vip3Aa7 with higher yields in the form of inclusion bodies demonstrated here would facilitate the development of a suitable formulation for the application of this class of insecticidal protein in the field, and the described system offers an additional method for potentially improving the efficacy of insecticides based on B. thuringiensis.