Bioprospecção e caracterização molecular de cepas de Bacillus Thuringiensis para o controle de lepidópteros-praga

Abstract

With the exponential growth of the world population, the demand for quality agricultural products, especially food sources for humans, has increased considerably. However, the attack of insect pests on crops contributes to a decrease in productivity and product quality. Control of these insects is carried out mainly through the use of chemical products, however, this type of control, despite being efficient, can result in unwanted side effects such as the selection of resistant insect populations, contamination of environments and the death of non-organic organisms. -target. An alternative consists of using Bacillus thuringiensis (Bt), a Gram-positive bacterium, occurring on different types of substrates, capable of producing protein crystals composed of Cry, Cyt toxins or secreted toxins such as VIP toxins. These toxins have high insecticidal activity against different orders of insects, being safe for humans and the environment. The objective of the work was to identify strains of B. thuringiensis from the Embrapa Maize and Sorghum Microorganism Bank that cause mortality greater than 90% for the lepidopteran pests Chrysodeixis includens, Spodoptera frugiperda, S. cosmioides, S. eriadania, and Helicoverpa armigera. For this, in selective bioassays with neonatal caterpillars of different pests, 80 strains of B. thuringiensis were used from the Embrapa Maize and Sorgo Microorganism Bank in Sete Lagoas - MG. The bioassays were carried out using 150 μL of the spore and crystal solution of each strain at a concentration of 1 × 108 spores/mL, and their mortality was evaluated for seven days. The experimental design used was completely randomized with experimental groups of four replications with 16 insects each. Nine of the eighty strains tested showed mortality above 90% for the species of C.includens, Spodoptera and H. armigera and none of them produced β-exotoxin. The strains of B. thuringiensis 1074F, 1090C, 1139E and 1166C showed mortality above 90% simultaneously for the five lepidopteran pest species tested and had their genome sequenced using the NGS platform with DNBSEQTM technology. We obtained 135 scaffolds resulting in a chromosome of 5,812,623 bp (1074F), 125 scaffolds in a chromosome of 5,783,457 bp (1090G), 135 scaffolds in a chromosome of 5,784297 bp (1139E) and 132 scaffolds in a chromosome of 5,820,845 bp (1166C), with G+C content ≥ 34% and a total of five genes coding for the insecticidal proteins Cry1Ib, Cry1Da, Vip1Ca, Vip2Ac and Vip3Ag, for the sequenced strains. Therefore, strains 1074F, 1090G, 1139E and 1166C demonstrated activity against the five species of C. includens, S. frugiperda, S. cosmioides, S. eridania and H. armigera and contain five insecticidal genes, demonstrating a potential to be used to produce new bioinsecticides and/or source of genes for the development of new events of transgenic plants resistant to insect pests.