Bacillus thuringiensis isolates were obtained from soil samples collected at different sites located in the same region but with different vegetation. The sites showed different frequencies of B. thuringiensis, depending on the type of vegetation. Strains of B. thuringiensis were found to be less common in samples of riparian forest soil than in soil of other types of vegetation. The rate of occurrence of B. thuringiensis in the samples also varied according to the vegetation. These results show that whenever this bacterium was found, it showed a high rate of occurrence, indicating that this species could be better adapted to using soil as a reservoir than other Bacillus species. The presence of cry genes was analyzed by polymerase chain reaction, and genes that exhibited activity against Diptera species were the most commonly found. The isolates obtained were characterized by random amplified polymorphic DNA, and 50% were clustered into clonal groups. These results demonstrated the possible occurrence of a high number of genetically similar strains when samples are collected from the same region, even if they are from locations with different vegetation.
Resumo -O objetivo deste trabalho foi selecionar e caracterizar molecularmente isolados de Bacillus thuringiensis tóxicos a Spodoptera eridania e S. frugiperda. Trinta e quatro isolados foram submetidos ao bioensaio, dos quais três foram selecionados e usados para a estimativa da CL 50 . Os isolados selecionados não diferiram da linhagem padrão HD-1. Na caracterização molecular, identificou-se a presença dos genes cry1 e cry2, nos isolados BR37 e BR94, e dos genes cry4A, cry4B, cry10, cry11 e cyt1 no isolado BR58, o que confirmou o perfil proteico obtido de 130, 70 e 65 kDa. Foram identificados cristais bipiramidais e esféricos. O isolado BR58, apesar de não conter os genes relacionados à toxicidade a Lepidoptera, causa mortalidade em ambas as espécies.Termos para indexação: Spodoptera eridania, Spodoptera frugiperda, controle biológico, genes cry, proteínas Cry. Selection and molecular characterization of Bacillus thuringiensisisolates for controlling Spodoptera spp.Abstract -The objective of this work was to select and molecularly characterize Bacillus thuringiensis isolates toxic to Spodoptera eridania and S. frugiperda. Thirty four isolates were subjected to the bioassay, of which three were selected and used to estimate the LC 50 . The selected isolates did not differ from the HD-1 standard line. In the molecular characterization, the presence of the cry1 and cry2 genes was identified in the BR37 and BR94 isolates, and of the cry4A, cry4B, cry10, cry11, and cyt1 genes in the BR58 isolate, which confirmed the obtained protein profile of 130, 70, and 65 kDa. Bipyramidal and spherical crystals were identified. The BR58 isolate, although not containing the genes related to toxicity to Lepidoptera, causes mortality in both species.
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