Genome sequence of a Vietnamese Bacillus thuringiensis strain TH19 reveals two potential insecticidal crystal proteins against Etiella zinckenella larvae

Abstract

The soybean pod borer Etiella zinckenella was considered to cause the most severe damage to soybean crop in many Asian countries. However, Bacillus thuringiensis is a spore-forming bacterium which is widely and effectively used for insects and nematodes management strategies as an eco-friendly biopesticide. Therefore, in this study, a whole genome of a promising indigenous Bt strain TH19 was sequenced and two potential insecticidal cry1 genes were revealed. Homology comparisons showed that the amino acid sequences of determined Cry1 proteins were 100% similar to those of the known truncated Cry1Aa4 and full length of Cry1Ia34 proteins in the NCBI database. The recombinant Cry1Aa4 and Cry1Ia34 proteins expressed in Escherichia coli strain BL21 (DE3) were confirmed by Western blot analysis. Insecticidal bioassays with neonatal larvae of E. zinckenella indicated that the toxicities of purified Cry1Aa4 and Cry1Ia34 intensely impacted to E. zinckenella lives, and their combination acted the most efficiently with relative LC50 values of 59.80 ng/cm2, 89.99 ng/cm2 and 38.33 ng/cm2. The histopathological modifications detected in midgut tissue included brush border membrane lysis, vesicles formation, disintegration of the apical membrane, and microvilli breakages. These results demonstrated that Cry1Aa4 and Cry1Ia34 proteins of Bt strain TH19 could account for key factors in biopesticide products against E. zinckenella.