Prospecção e análise genômica de cepas de bacillus thuringiensis eficientes no controle de Spodoptera eridania, Spodoptera cosmioides e Spodoptera frugiperda

Abstract

Despite Brazil being one of the main grain producers in the world, there are significant losses in production due to pests of the Spodoptera genus, especially the species S. frugiperda, S. eridania and S. cosmioides. These pests cause defoliation and direct damage to leaves and/or pods in different crops. Biological control with entomopathogenic microorganisms has been used effectively for years to manage pests. In particular, the bacterium Bacillus thuringiensis has been used in different formulations of bioinsecticides or as a source of insecticide genes for the development of transgenic plants. The aim of this work was to identify efficient B. thuringiensis strains against Spodoptera eridania, S. cosmioides and S. frugiperda caterpillars and the insecticide genes present in the strain with mortality above 90% for the three pests. Thirty strains of B. thuringiensis from the Collection of Microorganisms of Embrapa Milho and Sorgo in Sete Lagoas/MG, Brazil were used to carry out selective bioassays with newborn caterpillars of different pests. Bioassays were carried out using 150 uL of the solution containing spores and crystals of each strain at a concentration of 3 x 108 spores/mL, with mortality assessed for seven days. A completely randomized experimental design was used with 4 replications with 16 insects each. Six of the 30 strains of B. thuringiensis caused simultaneous mortality above 80% in three species of Spodoptera, and none of them produced β-exotoxin. The B. thuringiensis 1408 strain caused mortality above 90% for the three Spodoptera species, therefore, its genome was sequenced using the BGISEQ-500 platform. 39 scaffolds were obtained resulting in a chromosome of 5.196,838 bp, G+C content equal to 34.8%, 5.887 coding regions and a total of five genes encoding the insecticidal proteins Cry1Ib, Cry1Da, Vip1Ca, Vip2Ac and Vip3Ag. It was also evidenced that the insecticidal proteins Cry1Da and Vip3Ag, for having similarity less than 95% with those already deposited in banks, belong to new subclasses. Therefore, the B. thuringiensis 1408 was shown to be active against three important species of the Spodoptera genus and contains insecticide genes, which can be used for the production of new bioinsecticides and/or as a source of genes for the development of new events in transgenic plants resistant to pest insects.