Comparison of inclusions in differentBacillus thuringiensisstrains. An electron microscope study

A 54-kilodalton protein encoded by pBtoxis is required for parasporal body structural integrity in Bacillus thuringiensis subsp. israelensis

Strains of Bacillus thuringiensis such as B. thuringiensis subsp. israelensis (ONR-60A) and B. thuringiensis subsp. morrisoni (PG-14) pathogenic for mosquito larvae produce a complex parasporal body consisting of several protein endotoxins synthesized during sporulation that form an aggregate of crystalline inclusions bound together by a multilamellar fibrous matrix. Most studies of these strains focus on the molecular biology of the endotoxins, and although it is known that parasporal body structural integrity is important to achieving high toxicity, virtually nothing is known about the matrix that binds the toxin inclusions together. In the present study, we undertook a proteomic analysis of this matrix to identify proteins that potentially mediate assembly and stability of the parasporal body. In addition to fragments of their known major toxins, namely, Cry4Aa, Cry4Ba, Cry11Aa, and Cyt1Aa, we identified peptides with 100% identity to regions of Bt152, a protein coded for by pBtoxis of B. thuringiensis subsp. israelensis, the plasmid that encodes all endotoxins of this subspecies. As it is known that the Bt152 gene is expressed in B. thuringiensis subsp. israelensis, we disrupted its function and showed that inactivation destabilized the parasporal body matrix and, concomitantly, inclusion aggregation. Using fluorescence microscopy, we further demonstrate that Bt152 localizes to the parasporal body in both strains, is absent in other structural or soluble components of the cell, including the endospore and cytoplasm, and in ligand blots binds to purified multilamellar fibrous matrix. Together, the data show that Bt152 is essential for stability of the parasporal body of these strains.

A new serotype of Bacillus thuringiensis from Colombia toxic to mosquito larvae

During a survey conducted in Colombia a new isolate of Bacillus thuringiensis that showed toxicity toward Culex quinquefasciatus, Cx. pipiens, Aedes aegypti, and Anopheles stephensi larvae was isolated. Parasporal crystals were spherical in shape and showed a great degree of similarity with those produced by the reference strain of Bacillus thuringiensis subsp. israelensis. Supernatant fraction of the whole culture was not toxic, and heat-stable exotoxin production was negative. Catalase, urease, arginine dihydrolase, amylase, lecithinase, acetyl-methyl-carbinol, and gelatinase production were positive. Hemolysis on sheep blood agar was alpha-type. The isolate 163-131 showed natural resistance to azolocillin and was sensible to cephoperazone, cephalotin, nalidixic acid, and trimetoprin sulfametoxazole. Flagellar agglutination showed a specific H 30 antigen which allows individualization of this strain as a new serotype and the subspecies name of medellin is proposed.

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.

Intracellular crystal formation in Bacteroides nodosus

An intracellular crystalline structure was found in at least two strains of Bacteroides nodosus. The inclusion appeared to be associated with good growth of the organism under optimum conditions following selective passage of rough colonies containing highly fimbriate cells. Several morphological forms of the inclusion were noted. Indiscriminate subculture of crystal-forming cultures led to the loss of this particular property indicating a genetically controlled system of either bacterial or bacteriophage origin.