Toxicity of Bacillus thuringiensis to laboratory populations of the olive fruit fly (Dacus oleae)
A survey of Bacillus thuringiensis recovered from the environments of olive groves in Greece was carried out. Of 80 soil samples, 24 were found to contain B. thuringiensis with parasporal crystal inclusions; these were tested for toxicity against the olive fruit fly (Dacus oleae). Mortality levels of larvae caused by the different isolates varied from 7 to 87%. Higher levels of mortality were observed if a mixture of relatively pure crystals and spores was used compared with the mortality resulting from either fraction alone. We were able to show that the toxicity of the most active isolate is likely to be specific for D. oleae.
Purification and characterization of the entomocidal protoxin of Bacillus thuringiensis.
A procedure for purifying the insecticidal parasporal protoxin of Bacillus thuringiensis and a description of its biochemical and biophysical properties is provided. Mild alkali titration was necessary to generate a functional protoxin in a soluble form, and anion-exchange chromatography was used to remove contaminating cytoplasmic proteases that are nonspecifically bound to whole native parasporal crystals. Polyacrylamide gel electrophoresis, gel filtration chromatography, and meniscus depletion sedimentation equilibrium analysis revealed an apparent molecular weight for the protoxin of 1.34 x 10(5). The only NH2-terminal residue found was methionine. The soluble protoxin was 2.5 times more toxic to insect larvae than was the parasporal crystal. At alkaline pH the protoxin slowly converted to a low molecular weight toxin (apparent Mr = 6.8 x 10(4)). The molar specific toxicities of the protoxin and toxin were identical.
Alteration of Trichostrongylus colubriformis egg permeability by Bacillus thuringiensis israelensis toxin.
A toxin from the bacterium Bacillus thuringiensis israelensis is lethal to nematode eggs. Exposure of eggs of the ruminant nematode Trichostrongylus colubriformis to the toxin significantly increased the eggs' permeability to radiolabeled phenylalanine within 2 hr. Calcium chloride inhibited the toxin-induced change in egg permeability. Iodine staining of eggs that were exposed to the microbial toxin revealed that egg permeability was altered within 5 min and was dependent on the dose of toxin. Addition of 34 mM sucrose, 17 mM sodium chloride, or 17 mM potassium chloride to the eggs' medium increased the toxin's lethality. Exopeptidase activity in eggs of T. colubriformis was reduced significantly after exposure to the B. t. israelensis toxin. Tetrodotoxin, tetraethylammonium chloride, ouabain, 4-acetamido-4'-isothiocyano-stilbene-2,2'disulfonic acid (SITS), 4,4'-diisothiocyano-2,2'disulfonic acid stilbene (DIDS), valinomycin, and sodium vanadate, which affect membrane transport, had no significant effect on the activity of B. t. israelensis toxin for eggs. Likewise, a series of nucleotides and their derivatives had no effect on the toxin's activity. Ovicidal activity of the microbial toxin was increased by 4-aminopyridine (4.4 X), but was decreased by furosemide (97 X), nigericin (263 X), or monensin (125 X). Microscopic measurement of T. colubriformis eggs after treatment with the microbial toxin revealed no significant size change.