Characterization of two Bacillus thuringiensis isolates from South Brazil and their toxicity against Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Abstract

Abstract The entomopathogenic bacterium Bacillus thuringiensis (Bt) is the most widely used biopesticide. The specific toxic activity to insects and other organisms is related to the presence of crystals that have different morphologies, sizes, numbers and compositions according to the Bt strain. The crystals contain different proteins, which are encoded by distinct cry (crystal) genes. In this work, we have characterized two novel Bt strains isolated from the soils of south Brazil (named UNI498 and UNI872) and determined the lethal concentrations (LC50) of their crystal proteins to Anticarsia gemmatalis larvae. Serotyping of the new isolates was performed and the results indicated that UNI872 is a Bt serovar kurstaki and UNI498 is a Bt serovar aizawai. By transmission electron microscopy, we observed that UNI498 has crystals with cubic morphology whereas UNI872 has crystals with a bipyramidal shape. Polymerase chain reactions (PCRs) revealed the presence of cry1-like sequences in both isolates and a cry2-like gene in UNI 872. The cry1 fragments were sequenced and showed identities of 96 and 97% to known cry1A genes (UNI872 and UNI498, respectively). The presence of Cry1 proteins in both isolates was confirmed by SDS–PAGE. Bioassays to determine the LC50 were performed with A. gemmatalis third instar larvae using purified proteins. Results showed LC50s of 1.69 ng / cm 2 for UNI498 and 0.49 ng / cm 2 for UNI872.