Análise Genômica e Funcional de genes codificadores de proteínas inseticidas presentes em cepas de Bacillus thuringiensis eficientes no controle de lepidópteros-praga

Abstract

The constant attacks of pests in agriculture affect the productivity of important cultivars of Brazilian economy, such as maize, soybeans and cotton. The need to use ecologically viable alternatives, the entomopathogenic bacteria Bacillus thuringiensis (Bt) has won great visibility in the biological control of pests. Due to ability to produce a range of insecticidal proteins, has become important in the production of sprayable biopesticides and as source of insect pest resistance genes for development of transgenic plants. Therefore, with the discovery of potential strains to be used for this purpose, is essential for understanding the metabolism of each strain and for development of new products. The goal of this work was analyze the toxicity, explore the genomic content and select insecticidal genes from Bacillus thuringiensis potential strains. In the first approach, in vitro toxicity bioassays were performed with two B. thuringiensis strains (775E and 1608A) to determine the lethal concentrations (LC50 and LC90) against six species of lepidopteran pests (Anticarsia gemmatalis, Chrysodeixis includens Helicoverpa armigera, Spodoptera cosmioides, Spodoptera eridania and Spodoptera frugiperda). Both strains promoted high mortality rates of target insects, with highlighting to 1608A strain, which showed greater toxicity to A. gemmatalis and H. armigera. Greenhouse bioassays confirmed the effectiveness of this strain in reducing plant defoliation caused by targert pests. In the second approach, sequencing and genomic analysis of 1608A strain were performed and the insecticidal genes found were submitted to gene expression analysis by real time PCR at different stages of bacterial growth. The cry1Gb gene showed high expression during the sporulation phase and the toxicity of the protein encoded by it was confirmed by first time to C. includens. In the third approach, we present a complete genomic and comparative analysis of the Bacillus thuringiensis 775E strain, which has seven insecticidal genes of interest, similarity to other commercially important Bt strains, and several resistance and virulence genes in its genome.