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Studies onBacillus thuringiensis H-14 strains isolated in Egypt-II. Ultrastructure studies
A Abdel-Hameed1, K Lounatmaa, G Carlberg
1Department of Microbiology, Faculty of Pharmacy, Cairo University, Kasr-El-Aini Street, Cairo, Egypt.
Abstract:
Electron microscopy of thin sections of two mosqulto-toxic isolates ofBacillus thuringiensis H-14 showed inlcusions that varied in shape, size and stainability. The shape of some of these inclusions have not been reported before. Uitrastructural analysis of sporulation and parasporal crystal development shows that the insecticidal inclusions are initiated at the stage of axial filament formation during sporulation. In most of the inclusions there is a common subunit, formed first, which has a regular geometrical shape (rhomboid, hexagonal rectangular, trapezoid or pentagonal). Later added sub-units are more amorphous and this leads to a variety of inclusion shapes which appear at the end of sporulation. Some of these reguiar moleties develop in different ways, leading to cubical, rhomboid or parallelogramic-shaped crystais. In a freeze-tractured cell, the internal fracture faces of a crystal are seen. The size of the sub-units of this crystal was about 5×5 nm. For French summary, see next page.
Insights
Bacillus thuringiensis H-14 insecticidal inclusions exhibit diverse shapes and sizes, with unique ultrastructural development during sporulation. These findings reveal novel insights into parasporal crystal formation in mosquito-toxic bacteria.
Area of Science:
- Microbiology
- Insect Pathology
- Biochemistry
Background:
- Bacillus thuringiensis (Bt) H-14 is a key bacterium for mosquito control.
- Understanding the structure of its insecticidal inclusions is crucial for optimizing its efficacy.
- Previous studies have described various Bt crystal shapes, but novel forms and developmental pathways remain areas of investigation.
Purpose of the Study:
- To investigate the ultrastructure and development of insecticidal inclusions in two mosquito-toxic Bacillus thuringiensis H-14 isolates.
- To characterize the shapes, sizes, and subunit organization of parasporal crystals.
- To elucidate the initiation and assembly process of these insecticidal structures during sporulation.
Main Methods:
- Electron microscopy (thin sections and freeze-fracture) was employed to examine the morphology of inclusions.
- Ultrastructural analysis focused on sporulation and parasporal crystal development stages.
- Subunit size and organization within the crystals were analyzed.
Main Results:
- Inclusions displayed significant variation in shape, size, and stainability, with some previously unreported forms.
- Insecticidal inclusions initiated during axial filament formation in sporulation.
- A common, geometrically regular subunit formed first, followed by amorphous subunits, leading to diverse final inclusion shapes (cuboidal, rhomboid, etc.).
- Subunits measured approximately 5x5 nm in freeze-fractured crystals.
Conclusions:
- Bacillus thuringiensis H-14 parasporal crystal formation involves a complex, multi-stage process with a geometrically regular initial subunit.
- The observed diversity in inclusion morphology suggests varied developmental pathways and potential implications for insecticidal activity.
- This study provides novel ultrastructural details on Bacillus thuringiensis H-14 crystal development, contributing to the understanding of entomopathogenic bacteria.
