Activity of spores and extracellular proteins from six Cry+ strains and a Cry- strain of Bacillus thuringiensis subsp. kurstaki against the western spruce budworm, Choristoneura occidentalis (Lepidoptera: Tortricidae).
ABSTRACT We characterized insecticidal activity of previously untested strains of Bacillus thuringiensis kurstaki belonging to two crystal serovars (K-1 and K-73) against the western spruce budworm (Choristoneura occidentalis Freeman 1967). By testing various components, we demonstrated that spores play a critical role in the pathogenesis of each strain. Spore-free crystals caused low mortality and purified spores were generally not toxic. The addition of spores to purified protoxin increased toxicity several hundred-fold, regardless of the parental strain from which the spores or protoxins were derived. The crystal and spore components did not account for full insecticidal activity of whole sporulated cultures owing to the toxicity of soluble proteins that are secreted during cell growth. We observed a marked difference in toxicity of secreted proteins between the K-1 and K-73 type strains, with the K-1 preparations causing much higher mortality, mass reduction, and inhibition of pupation. There was a consistent correlation between relative toxicity of secreted protein preparations and the presence and quantity of the Vip3A protein, suggesting that this protein contributes to the virulence of B. thuringiensis subsp. kurstaki in western spruce budworm larvae. However, other virulence factors have to be invoked to explain the synergizing effect of spores from both K-1 and K-73 strains on Cry protein toxicity.
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ABSTRACT: The toxicity of nine Bacillus thuringiensis Cry proteins against neonate Earias insulana larvae was tested using a mixture of crystals and spores. The mean lethal concentration (LC50) of Cry1Ac was 1.99 μg/ml. Cry1Fa, Cry1Ca, Cry1Ja and Cry2Aa were more active than Cry1Ac, with LC50 values of 0.22, 0.24, 0.29, 0.43 μg/ml, respectively. Cry1Da and Cry1Aa were considerably less active than Cry1Ac. The remaining proteins, Cry1Ba and Cry1Ab, displayed no activity. Relative potencies were also calculated. Cry1Ja and Cry1Fa were significantly more active (7.72 and 5.71 times, respectively) than Cry1Ac, while Cry1Ca was significantly (1.95 times) more active than Cry2Aa.Crop Protection 01/2011; 30(8):1024-1027. · 1.54 Impact Factor
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ABSTRACT: Bacillus thuringiensis (Bt) strains were isolated from soil samples of Great Nicobar Islands, one of the "hottest biodiversity hotspots," where no collection has been characterized previously. The 36 new Bt isolates were obtained from 153 samples analyzed by crystal protein production with light/phase-contrast microscopy, determination of cry gene profile by SDS-PAGE, evaluation of toxicity against Coleopteran, and Lepidopteran insect pests, finally cloning and sequencing. Majority of the isolates showed the presence of 66-35 kDa protein bands on SDS-PAGE while the rest showed >130, 130, 73, and 18 kDa bands. The variations in crystal morphology and mass of crystal protein(s) purified from the isolates of Bt revealed genetic and molecular diversity. Based on the toxicity test, 50 % of isolates were toxic to Ash weevils, 16 % isolates were toxic to cotton bollworm, 38 % isolates were toxic both to ash weevil as well as cotton bollworm, while 11 % of the isolates did not exhibit any toxicity. PCR analysis unveiled prepotency of cry1B- and cry8b-like genes in these isolates. This study appoints the first isolation and characterization of local B. thuringiensis isolates in Great Nicobar Islands. Some of these isolates display toxic potential and, therefore, could be adopted for future applications to control some agriculturally important insect pests in the area of integrated pest management for sustainable agriculture.Current Microbiology 02/2013; · 1.52 Impact Factor
- Value in Health 01/2000; 3(2):60-60. · 2.19 Impact Factor