Abstract
Bacillus thuringiensis is gaining worldwide importance in the control of pests in agriculture and public health. Characterization of new isolated strains with original, higher and broader spectrum of activity is an ever developing field. Parasporal inclusions from BLB427, a new B. thuringiensis strain isolated from Tunisian soil, contained 2 major Cry proteins having molecular weights of about 130-135 kDa and 65-70 kDa corresponding to cry1-type and cry2-type genes, respectively. These toxins exhibited high toxicities to Ephestia kuehniella and Spodoptera littoralis larvae, with LC50 values of about 81.91 µg/cm2 (+/- 15.30) and 79.70 µg/cm2 (+/- 36.73), respectively. BLB427 supernatant showed a promising activity against Lepidopteran pests due to the presence of vip3-type gene in this strain. The high toxicity of BLB427 supernatant compared to that of BUPM95, used as control, was due in part to the high copy number of vip3 gene of BLB427 compared to that of vip3Aa16 of BUPM95, as demonstrated by Real-time PCR. This gene was cloned, sequenced and the comparison with the most known vip3 genes in databases, demonstrated that vip3(427) gene and the corresponding protein showed differences that can influence the efficiency of the Vip3(427) toxin against Lepidoptera. After overexpression of Vip3(427) protein in Esherichia coli and its purification using His-Trap column, the toxin showed a promising toxicity against the lepidopteran pest S. littoralis with extremely damages in the larvae midgut traduced by the vacuolization of the apical cells, the damage of microvilli and the disruption of epithelial cells. The results described in the present study proved that B. thuringiensis BLB427 strain could be of a great interest for lepidopteran biocontrol by using its d-endotoxins and/or Vip3 toxins in bioinsecticides formulations.
Highlights
Biomolecules derived from Bacillus thuringiensis are gaining worldwide importance as environmentally desirable alternatives to synthetic chemicals for pests control in public health and agriculture [1]
The Vegetative insecticidal proteins (Vip) have been classified into three groups according to their sequence homology: Vip1 and Vip2 proteins that act as binary toxin and are toxic to Coleoptera [6] and Vip3 proteins known by their activity against Lepidoptera [7]
BLB427 crystal protein content BLB427 is one of the promising B. thuringiensis strains isolated by Boukedi et al [10]
Summary
Biomolecules derived from Bacillus thuringiensis are gaining worldwide importance as environmentally desirable alternatives to synthetic chemicals for pests control in public health and agriculture [1]. This Gram-positif soil bacterium is known by its ability to produce crystalline inclusions during sporulation. Corresponding author: Lobna Abdelkefi-Mesrati; E. mail: Department of Biology, Faculty of Sciences and Arts-Khulais, University of Jeddah, Saudi Arabia. Due to their high efficiency in the biological control of pests, the repetitive use of some Cry toxins contributed to the resistance emergence to these Cry proteins in some insect populations. Cry and Vip proteins of BLB427 demonstrated an interesting activity against different lepidopteran pests such as Ephestia kuehniella and Spodoptera littoralis
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