Effect of Bacillus thuringiensis biomass and insecticidal activity by cultivation with vegetable wastes

Bacillus thuringiensis (Bt) has been regarded as a biopesticide with high efficiency and safety, while it still cannot be popularized and mass-produced because of its high production costs. In the present study, we aimed to develop a cost-effective biopesticide via the secondary use of discharged vegetable wastes as the raw fermentation medium, and the insecticidal activity of Bt strain prepared by this cheap cultivation approach was evaluated. The suitable carbon source, nitrogen source additives and optimal metal ions were screened by the single-factor test, and the optimal combination of additives was determined by orthogonal test and ANOVA analysis. We found that soluble starch (6 g l^-1), soya bean meal (6 g l^-1), Al³⁺ (0.4 g l^-1) and Fe²⁺ (0.4 g l^-1) were the optimal exogenous additives, and the optimal fermentation conditions were as follows: pH 7.0, temperature of 35°C and aeration of 80 ml/250 ml. Meanwhile, the bioactivity test results showed that the Bt strain prepared by cheap cultivation still exhibited a good insecticidal effect on Helicoverpa armigera compared with the standard LB medium. Collectively, our findings provided a new strategy for vegetable waste utilization with less environmental impact and reduced production cost.