Crystal-forming bacteria as insect pathogens

Studies onBacillus thuringiensis H-14 strains isolated in Egypt-II. Ultrastructure studies

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.

Crystal-forming proteins of Bacillus thuringiensis. The limited hydrolysis by endogeneous proteinases as a cause of their apparent multiplicity

The crystals of the entomocidal protein of Bacillus thuringiensis are admixed with proteinases that in the course of their dissolution cause gradual degradation of the "genuine" crystal-forming protein components (i.e. the primary biosynthetic products) to products of lower molecular weight. This phenomenon might explain at least partially the contradictory data on the molecular parameters of the crystal-forming proteins. Preliminary inactivation of the proteinases adsorbed on the crystals allowed us to eliminate this source of the artefacts and to gain more reliable data on the protein composition of the crystals formed by various strains of B. thuringiensis. It has been shown that the crystals formed by all serotypes of B. thuringiensis, with the exception of the serotype V, contain only one protein with a mol. wt. of 145000, 135000 or 130000, depending on the strain. The majority of the strains that belong to the serotype V form crystals consisting of two proteins with mol. wts. of 135000 and 130000, but some of them also have a third component with a mol. wt. of 65000.

Inactivation of Bacillus thuringiensis spores by ultraviolet and visible light

The inactivation of Bacillus thuringiensis spores and spores treated with two protectants, one proteinaceous and the other a commercial product, Shade, at wavelengths of the near-ultraviolet and visible spectra and at 254 nm is described. Determination of the inactivating wavelengths may be used to establish an efficient sunlight protective system for B. thuringiensis when used as a microbial insecticide.