Identification and analysis of toxins in novel Bacillus thuringiensis strain Bt S3076-1 against Spodoptera frugiperda and Helicoverpa armigera (Lep.: Noctuidae).

Despite the successful application of toxins from Bacillus thuringiensis as biological control agents against pests, pests are showing resistance against an increasing number of Bacillus thuringiensis toxins due to evolution; thus, new toxins with higher toxicity and broad-spectrum activity against insects are being increasingly identified. To find new toxins, whole genome sequencing of the novel B. thuringiensis strain Bt S3076-1 was performed, and ten predicted toxic genes were identified in this study, including six cry genes, two tpp genes, one cyt gene and one vip gene, among which six were novel toxins. Subsequently, SDS‒PAGE analysis showed that the major proteins at the spore maturation stage were approximately 120 kDa, 70 kDa, 67 kDa, 60 kDa and 40 kDa, while active proteins after trypsin digestion (approximately 70 kDa and 40 kDa) exhibited LC values of 149.64 μg/g and 441.47 μg/g against Spodoptera frugiperda and Helicoverpa armigera larvae, respectively. Furthermore, pathological observation results showed that the peritrophic membrane of Spodoptera frugiperda and Helicoverpa armigera larvae was degraded. These findings will provide an experimental reference for further research on the insecticidal activity, toxicity spectrum and synergism of these toxins in Bt S3076-1.