Abstract
Bacillus thuringiensis (Bt) is a well-known entomopathogen. In this study, we cloned the vip3Aa1 gene from Bt strain GIM1.147 and investigated the insecticidal activity of Bt Vip3Aa1 protein produced by Escherichia coli against Periplaneta americana and Blattella germanica. The results showed that purified Vip3Aa1 exhibited an LC(50) at 24 h against P. americana and B. germanica of 0.182 mg·ml(-1) and 0.276 mg·ml(-1), respectively. Investigations of its mode of action showed that Vip3Aa1 could be proteolyzed into a 62-kDa toxic protein by P. americana gut-soluble proteases. In addition, Vip3Aa1 caused severe damage to the columnar colon and the midgut, as observed through hematoxylin-eosin staining and scanning electron microscopy. The 62-kDa activated Vip3Aa1 protein could form ion channels in the colon and the midgut in vitro. Based on protease activity analysis, Vip3Aa1 at concentrations of 0.125 mg·ml(-1) and 0.031 mg·ml(-1) could downregulate the activities of glutathione S-transferase, α-NA esterase, trypsin, and chymotrypsin. This report provides the first description of the activity of Vip3Aa1 toxins toward P. americana and B. germanica and demonstrates that the mechanism through which Vip3Aa1 kills P. americana and B. germanica differs from that involved in the killing of lepidopteran insects.