Water stress and limited aeration imparted by solid-state fermentation (SSF) were reported as crucial factors for the enhancement of endospore production by Bacillus thuringiensis (Bt);and thus, more δ-endotoxin coul...Water stress and limited aeration imparted by solid-state fermentation (SSF) were reported as crucial factors for the enhancement of endospore production by Bacillus thuringiensis (Bt);and thus, more δ-endotoxin could be produced concomitantly with reduced time. Therefore, Bt subsp. kurstaki (Btk) was employed in the present study to evaluate its efficiency for the concomitant production of endospores and δ-endotoxin in LB medium supplemented with various naturally available agricultural products, i.e., flours of soybean, Bengal gram or jack seed at various concentrations (10%, 20%, 30%, 40%, 50%, 60%, 80% or 100%, all w/v). After 12 h fermentation, the supernatant in it was centrifuged off aseptically to obtain solid substrate for subsequent SSF. Of them, soybean (30%) supplemented medium was the best for the enhanced production of endospore and δ-crystals. The maximum yield of endospores during solid-state fermentation was observed 48 h, i.e., compared to submerged fermentation in LB, it was 24 h less gestation period. In control sample, the endospores achieved the maximum length (1.10 ± 0.13 μm) and diameter (0.63 ± 0.07 μm) at 72 h;while in soybean supplemented medium, the maximum length (2.10 ± 0.16 μm) and diameter (1.63 ± 0.16 μm) were at 48 h and 72 h, respectively. Upon staining, acridine orange specifically stained the endospores;malachite green-saffranin stained both δ-crystals and endospores;and coomassie brilliant blue specifically stained δ-endotoxin. Briefly, normal gestation period or harvest time for Btk is 72 h, which could be reduced to 48 h, if SSF is employed as demonstrated in this study.展开更多
The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is among the most destructive pests that attack tomato in many countries. In this study, the efficiency of three suspensions (106;105;104 cell/...The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is among the most destructive pests that attack tomato in many countries. In this study, the efficiency of three suspensions (106;105;104 cell/ml) of Bacillus thuringiensis var. Kurstaki was tested on T. absoluta larvae 1st, 2nd, 3rd and 4th instar was assessed to study the effect of these suspensions on larval mortality. Results showed that the concentration 106 cell/ml resulted in the highest mortality of all instars larvae with an average mortality of 20%, 22.66%, 18.66% and 23.33% was recorded for the first, second, third and fourth instar, respectively. The greatest percentage of mortality occurred in the third day after the larvae fed with leaves treated with suspension B. thuringiensis.展开更多
To evaluate phylogenetic relatedness as a proxy for susceptibility to Bacillus thuringiensis （Bt） when selecting species to act as surrogates for others in prerelease test- ing, we examined the responses of 11 labor...To evaluate phylogenetic relatedness as a proxy for susceptibility to Bacillus thuringiensis （Bt） when selecting species to act as surrogates for others in prerelease test- ing, we examined the responses of 11 laboratory-reared lepidopteran colonies, comprising members of 2 families, 5 genera, and 9 species, to a commercial Bt preparation. Sur- vival, pupal mass, and timing of pupation and adult emergence of 2 noctuids （Spodoptera litura and Helicoverpa armigera） and 7 tortricids （Cnephasia jactatana, Ctenopseustis obliquana, Ctenopseustis herana, Planotortrix octo, Planotortrix notophaea, Planotor- trix excessana [2 different laboratory colonies], and Epiphyas postvittana [2 colonies]） were examined after feeding first instar larvae with artificial diet containing 5 μL/100 mL Dipel ES （Bt subsp, kurstaki）. Bt caused significant larval mortality in all species except S. litura, in which only pupation was delayed compared with untreated controls. Neither of the noctuid species tested would act as a suitable surrogate for the other in tests of Bt impacts on survival. With the exception of the 2 colonies orE. postvittana, which differed from each other not only in their responses to Bt but also in their development times when not treated with Bt, species within each tortricid genus had similar responses to Bt and thus could act as surrogates for each other. Members of different genera within this family could represent each other only if relatively coarse measurement endpoints （e.g., toxic or not） were considered adequate for assessing risks to nontarget species in the field.展开更多
文摘Water stress and limited aeration imparted by solid-state fermentation (SSF) were reported as crucial factors for the enhancement of endospore production by Bacillus thuringiensis (Bt);and thus, more δ-endotoxin could be produced concomitantly with reduced time. Therefore, Bt subsp. kurstaki (Btk) was employed in the present study to evaluate its efficiency for the concomitant production of endospores and δ-endotoxin in LB medium supplemented with various naturally available agricultural products, i.e., flours of soybean, Bengal gram or jack seed at various concentrations (10%, 20%, 30%, 40%, 50%, 60%, 80% or 100%, all w/v). After 12 h fermentation, the supernatant in it was centrifuged off aseptically to obtain solid substrate for subsequent SSF. Of them, soybean (30%) supplemented medium was the best for the enhanced production of endospore and δ-crystals. The maximum yield of endospores during solid-state fermentation was observed 48 h, i.e., compared to submerged fermentation in LB, it was 24 h less gestation period. In control sample, the endospores achieved the maximum length (1.10 ± 0.13 μm) and diameter (0.63 ± 0.07 μm) at 72 h;while in soybean supplemented medium, the maximum length (2.10 ± 0.16 μm) and diameter (1.63 ± 0.16 μm) were at 48 h and 72 h, respectively. Upon staining, acridine orange specifically stained the endospores;malachite green-saffranin stained both δ-crystals and endospores;and coomassie brilliant blue specifically stained δ-endotoxin. Briefly, normal gestation period or harvest time for Btk is 72 h, which could be reduced to 48 h, if SSF is employed as demonstrated in this study.
文摘The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is among the most destructive pests that attack tomato in many countries. In this study, the efficiency of three suspensions (106;105;104 cell/ml) of Bacillus thuringiensis var. Kurstaki was tested on T. absoluta larvae 1st, 2nd, 3rd and 4th instar was assessed to study the effect of these suspensions on larval mortality. Results showed that the concentration 106 cell/ml resulted in the highest mortality of all instars larvae with an average mortality of 20%, 22.66%, 18.66% and 23.33% was recorded for the first, second, third and fourth instar, respectively. The greatest percentage of mortality occurred in the third day after the larvae fed with leaves treated with suspension B. thuringiensis.
文摘To evaluate phylogenetic relatedness as a proxy for susceptibility to Bacillus thuringiensis （Bt） when selecting species to act as surrogates for others in prerelease test- ing, we examined the responses of 11 laboratory-reared lepidopteran colonies, comprising members of 2 families, 5 genera, and 9 species, to a commercial Bt preparation. Sur- vival, pupal mass, and timing of pupation and adult emergence of 2 noctuids （Spodoptera litura and Helicoverpa armigera） and 7 tortricids （Cnephasia jactatana, Ctenopseustis obliquana, Ctenopseustis herana, Planotortrix octo, Planotortrix notophaea, Planotor- trix excessana [2 different laboratory colonies], and Epiphyas postvittana [2 colonies]） were examined after feeding first instar larvae with artificial diet containing 5 μL/100 mL Dipel ES （Bt subsp, kurstaki）. Bt caused significant larval mortality in all species except S. litura, in which only pupation was delayed compared with untreated controls. Neither of the noctuid species tested would act as a suitable surrogate for the other in tests of Bt impacts on survival. With the exception of the 2 colonies orE. postvittana, which differed from each other not only in their responses to Bt but also in their development times when not treated with Bt, species within each tortricid genus had similar responses to Bt and thus could act as surrogates for each other. Members of different genera within this family could represent each other only if relatively coarse measurement endpoints （e.g., toxic or not） were considered adequate for assessing risks to nontarget species in the field.
