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Abstract

Abstract

B. thuringiensis is a gram-positive bacterium which produces, during sporulation, crystalline inclusions containing one or more delta-endotoxins. The latter are selectively toxic against a wide variety of insects, including important pests. Formulations based on B. thuringiensis have been used safely in developed countries as bioinsecticides for agriculture, forestry and disease vector control. This kind of bioinsecticides occupies the first place in the biopesticides world market and is essential for crop protection. The importance of such bioinsecticides and the emergence of new insect resistance cases, promoted worldwide isolation and screening programmes of new strains with particularly high insecticidal activities.

This project aims to develop an integrated approach that will explore activities of new B. thuringiensis isolates from Qatar and the Gulf region, an unexplored region, by performing an important programme of B. thuringiensis strains isolation from Qatar, screening using modern molecular techniques, gene investigation and bioassays.

The screening of 151 B. thuringiensis strains isolated from Qatar, allowed the evidence of strains having different crystal forms. In fact, these strains produce parasporal crystals that have pyramidal, bipyramidal, cubical, spherical and amorphous forms. These results demonstrate the heterogeneity and the fact that they produce different bioinsecticides acting on different insect families. Among these B. thuringiensis strains, only 58 strains produce bipyramidal crystals (38 %).

Similar results were obtained in the laboratory by Al-Zahra Attar and Sara Zakzouk who have screened respectively 199 and 87 other strains and obtained about the same ratio of bipyramidal crystal producing strains. The latter plasmid DNAs were analyzed showing different plasmid patterns. These results demonstrate that the bipyramidal crystal producing strains belong to different families. By PCR and electrophoresis of the amplified DNA fragments, we could predict the nature of the delta-endotoxin coding genes and the delta-endotoxin insecticidal activities. All the studied strain has protease activities except one that is protease minus. Such is very rare among Bacillus thuringiensis strains, but exists in Qatar. This strain is of high industrial value, since preventing proteolysis of delta-endotoxin and secreted active proteins and enzymes and could be considered as a suitable host for stable heterologous gene expression and protein secretion.

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/content/papers/10.5339/qfarf.2011.EVPS2
2011-11-20
2019-11-16
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