Screening of Vip3Aa60 and Vip3Ad5 and characterization of their binding to Spodoptera exigua midguts

- Vip3Aa60 and Vip3Ad5 were screened from Bacillus thuringiensis strains.
- Toxicity assays of Vip3Aa60 and Vip3Ad5 were performed against Spodoptera exigua.
- Vip3Aa60 bound to brush border membrane vesicles (BBMV) of S. exigua at higher affinity than Vip3Ad5.

Vip3A proteins, which shared no sequence or structural homology with the crystal proteins, were considered as a new generation of Bacillus thuringiensis toxins. In this study, we screened two novel vip3A genes from a number of B. thuringiensis strains, which were classified as vip3Aa60 and vip3Ad5 respectively. The full length of Vip3Aa60 and Vip3Ad5 showed 85% identity and their C-terminal domains showed 79.05% homology. The activity of both toxins was estimated against important lepidopteran pest (Spodoptera exigua). Vip3Aa60 revealed high toxicity against S.exigua as the LC50 value was 108.92 ng cm−2 and Vip3Ad5 displayed low toxicity against S.exigua (LC50 >4000 ng cm−2). In their binding assays, both Vip3Aa60 and Vip3Ad5 could bind to the Brush Border Membrane Vesicles (BBMV) of S. exigua and the affinity of binding to BBMV was significantly higher for Vip3Aa60 than Vip3Ad5. These results may provide useful information for insecticidal mechanism research of Vip3A against S. exigua.

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