The correlation of the presence and expression levels of cry genes with the insecticidal activities against Plutella xylostella for Bacillus thuringiensis strains.

Ming-Lun Chen,Chin-Fa Hwang,Pin-Hsin Chen,Chia-Wei Lin,Hau-Yang Tsen,Jen-Chieh Pang

doi:10.3390/toxins6082453

Ming-Lun Chen, Chin-Fa Hwang + Show 4 more

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https://doi.org/10.3390/toxins6082453

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Abstract

The use of Bacillus thuringiensis (Bt) strains with high insecticidal activity is essential for the preparation of bioinsecticide. In this study, for 60 Bt strains isolated in Taiwan, their genotypes and the correlation of some cry genes as well as the expression levels of cry1 genes, with their insecticidal activities against Plutella xylostella, were investigated. Pulsed field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) results revealed that the genotypes of these Bt strains are highly diversified. Also, a considerable number of the Bt strains isolated in Taiwan were found to have high insecticidal activities. Since strains that showed individual combined patterns of PFGE and RAPD exhibited distinct insecticidal activities against P. xylostella, thus, these genotypes may be useful for the identification of the new Bt strains and those which have been used in bioinsecticides. In addition, although the presence of cry2Aa1 may have a greater effect on the insecticidal activity of Bt strains in bioassay than other cry genes, only high expression level of cry1 genes plays a key role to determine the insecticidal activity of Bt strains. In conclusion, both RAPD and PFGE are effective in the differentiation of Bt strains. The presence of cry2Aa1 and, especially, the expression level of cry1 genes are useful for the prediction of the insecticidal activities of Bt strains against P. xylostella.

Highlights

Bacillus thuringiensis (Bt) is a gram positive, endospore forming bacterium of the B. cereus group that forms a parasporal crystal (δ-endotoxins or Cry toxins) during the stationary phase of its growth cycle [1]
For Bt, the production of insecticidal crystal inclusion inside the cell during sporulation, is controlled by cry genes, which are usually located on the plasmid [5]
The genotypes of Bt strains, if determined by highly discriminatory methods, may allow us to identify the newly isolated strains with potential for pesticide use and those strains which have been used in bioinsecticides

Summary

Introduction

Bacillus thuringiensis (Bt) is a gram positive, endospore forming bacterium of the B. cereus group that forms a parasporal crystal (δ-endotoxins or Cry toxins) during the stationary phase of its growth cycle [1]. The crystal consists of proteins exhibiting a highly specific insecticidal activity to a limited number of insect species [2,3]. Due to the insecticidal properties of Bt, products based on. Bt toxins have been well recognized for the biological control of insect pests in forestry and agriculture for decades [4]. For Bt, the production of insecticidal crystal inclusion inside the cell during sporulation, is controlled by cry genes, which are usually located on the plasmid [5]. More than 70 groups of Cry toxins have been identified [7]. Major classes of Bt toxins include Lepidoptera-active Cry, Lepidoptera and Diptera-active Cry, Coleoptera-active Cry, and Diptera-active Cry4 [8]

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