Specificity of Bacillus thuringiensis Delta-Endotoxin

The insecticidal activity of the delta-endotoxins of 14 Bacillus thuringiensis strains belonging to 12 subspecies was determined against Pieris brassicae, Heliothis virescens, and Spodoptera littoralis. Larvae of P. brassicae were highly susceptible to purified crystals of strains of B. thuringiensis subsp. thuringiensis and B. thuringiensis subsp. morrisoni, whereas H. virescens responded best to B. thuringiensis subsp. kenyae and B. thuringiensis subsp. kurstaki. The crystals of the B. thuringiensis subsp. entomocidus strain were the most potent against S. littoralis. It was shown that the solubility of the crystals within the gut of the three insect species is a first important step in the mode of action. Predissolution of the crystals especially enhanced the insecticidal activity against H. virescens. When in vitro-activated toxins were applied, the relative potency range varied greatly from one insect species to another. It can be concluded that at least three factors influence the potency of B. thuringiensis delta-endotoxins: the strain-related origin of the toxin, the degree of solubility of the crystals in the gut juice, and the intrinsic susceptibility of the insect to the toxin.     

Bacillus thuringiensis isolates from Egyptian soils and their potential activity against lepidopterous insects

This study aims to search for indigenous Bacillus thuringiensis (Bt) strains from the soils of different locations representing 11 Egyptian governorates. A total of 2671 colonies from 93 soil samples were examined. The total number of Bt positive soil samples was 40/93 i.e. 43.01%. The results indicate that the percentage of the occurrence of Bt in these samples was 3.818%. The Egyptian soil showed to be rich in Bt. The evaluation of the potential activity of 40 positive soil isolates against Spodoptera littoralis and Helicoverpa (=Heliothis) armigera was carried out. Subsequently, LC₅₀ and LC₉₀ values and the potency of the Bt isolates were determined when applied against the target insects with reference to three standard preparations.     

Bacillus thuringiensis isolates from soil and diseased insects in Egyptian cotton fields and their activity against lepidopterous insects

The distribution of Bacillus thuringiensis in Egyptian soils of cotton cultivations represented by 11 governorates was studied. This study aimed to isolate indigenous strains that may be potent against some lepidopterous insect pests. Out of 45 isolates, only 10 were effective and they showed high levels of toxicity against the target insects at 500 μg/ml (80% larval mortality or higher). Among these 10 isolates, two isolates were potent against Spodoptera littoralis, two isolates were potent against Helicoverpa (= Heliothis) armigera, seven isolates were potent against Pectinophora gossypiella, but none were potent against Agrotis ypsilon. LC₅₀ and LC₉₀ values and the potency of the B. thuringiensis isolates have been determined. Trials were conducted to isolate B. thuringiensis from diseased lepidopterous insects collected from the same locations, but all isolates showed low potential activity against the target insects. These findings showed promise for the possible use of some indigenous B. thuringiensis strains in the control of lepidopterous pests in Egypt.     

昆虫Bt毒素受体蛋白的研究进展

Bt是一种被广泛应用的生物杀虫剂,昆虫Bt受体蛋白在Bt发挥毒性过程中起到非常重要的作用,而且受体蛋白与Bt结合能力的改变可能是昆虫对Bt产生抗性的主要原因,近年来已成为国际研究的热点。该文从昆虫Bt受体蛋白的分离鉴定,结合动力学,与Bt杀虫毒性、抗性的关系及其分子本质等方面综述受体蛋白的研究进展。     

土壤来源苏云金芽孢杆菌的形态,δ—内毒蛋白质及其...

94 strains of Bacillus thuringiensis were isolated from soils in southwest and northwest of China. The morphology of cells, spores and parasporal crystals of these strains was investigated under transmission and scanning electro-microscope. Proteins of delta-endotoxins from all strains were analysed by rapid SDS-PAGE. 9 species of insects in Lepidoptera, Coleoptera and Diptera were tested for assay of delta-endotoxins. Some kinds of parasporal crystals were quite different in form and in composition of protein from those reported before. Most of strains were nontoxic to all of 9 species used in bio-assay. Some strains were very effective in species of Coleoptera or Noctuidae.     

Diversity of Colombian strains of Bacillus thuringiensis with insecticidal activity against dipteran and lepidopteran insects

AIM: To evaluate the genetic and molecular diversity and insecticidal activity of Bacillus thuringiensis isolates from all the natural regions of Colombia. METHODS AND RESULTS: A total of 445 isolates from a collection of B. thuringiensis were characterized. The parasporal crystal morphology that was most abundant was bipyramidal (60%). Almost 10% of the isolates were toxic to Spodoptera frugiperda and 5.6% against Culex quinquefasciatus larvae. cry gene content determined by PCR indicated that 10.6% of the isolates contained cry1 genes and 1.1% contained cry2, cry4 or cry11 genes. Protein content of the parasporal crystal was determined by SDS-PAGE; 25 and 18 different protein profiles were found in isolates active against S. frugiperda and C. quinquefasciatus, respectively. CONCLUSIONS: Bacillus thuringiensis presents great genetic and molecular diversity even in isolates from the same soil sample. Moreover, the diversity and activity of the isolates might have a relationship with the geographical origin of the samples. SIGNIFICANCE AND IMPACT OF THE STUDY: The results obtained here indicate that some of the B. thuringiensis isolates characterized in this study are potential control agents that could be used in programmes against mosquitoes and S. frugiperda.     

A novel strain of Bacillus thuringiensis (NCIMB 40152) active against coleopteran insects

Abstract: A novel Bacillus thuringiensis strain, NCIMB 40152, was isolated from dead Tenebrio molitor L. larvae. The isolate is endowed with specific insecticide activity against the Colorado potato beetle ( Leptinotarsa decemlineata (Say), Coleoptera, Crysomelidae), but has no effect against lepidopteran or dipteran insects.
During the sporulation process it produces diamond-shaped crystals and small inclusions. Rare flat, square crystals are alsò produced. The strain can be differentiated from the other reported B. thuringiensis strains active against Coleoptera on the basis of physiological and biochemical tests, flagellar serotype and toxin electrophoretic patterns.
NCIMB 40152 toxin is easily extractable from spore/crystal preparations in neutral distilled water without detergents or reducing agents.     

Biocontrol efficacy of protoplast fusants between Bacillus thuringiensis and Bacillus subtilis against Spodoptera litura Fabr.

Bacillus thuringiensis (Bt) is a microbial pesticide widely used to control crop pests. Its strains have good biocontrol activity against crop insect pest, but lack some desirable characteristics that are found in Bacillus subtilis. An attempt has been made to combine those desirable characteristics; we used a highly effective biocontrol strain of B. thuringiensis in protoplast fusions with a strain of B. subtilis. The fusants were identified through cell culture and stained with crystal violet. The Bt and B. subtilis protoplasts were induced to fuse by PEG 6000. The fusants were produced almost 95% mortality in first instar larvae of Spodoptera litura. The lethal doses (The LC₅₀ and LC₉₀) for mortality of S. litura values were significantly in lower level in the fusant-treated larvae, when compared with Bt and B. subtilis individual treatment. The consumption and digestion of S. litura significantly decreased after treatment with fusant. Also the approximate digestibility of S. litura increased significantly.     

Avidin, a potential biopesticide and synergist to Bacillus thuringiensis toxins against field crop insects

A meridic diet was supplemented with avidin at various concentrations to determine its effects on growth and mortality of three lepidopteran insects: Helicoverpa zea (Boddie), Spodoptera exigua (Hübner), and Anticarsia gemmatalis (Hübner). All insects were placed on diet immediately after hatching and observed until death or pupation occurred. At a concentration of 10 ppm, avidin had little or no effect on growth and mortality compared with the control. However at a concentration of 100 ppm almost all tested insects were killed. H. zea was further tested by adding sublethal concentrations of Bt (CrylAc) in the diet containing avidin. The synergistic effect was significant, with mortality increasing to 44.4% over additive mortality (21.6%) of Bt and avidin.     

Characterization of a Bacillus thuringiensis strain with a broad spectrum of activity against lepidopteran insects

The insect pathogen Bacillus thuringiensis is suitable for use in biological control, and certain strains have been developed as commercial bioinsecticides. The molecular and biological characterization of a Bacillus thuringiensis subsp. aizawai strain, named HU4‐2, revealed its potential as a bioinsecticide. The strain was found to contain eight different cry genes: cry1Ab, cry1Ad, cry1C, cry1D, cry1F, cry2, cry9Ea1, and a novel cry1I‐type gene. Purified parasporal crystals from strain HU4‐2 comprised three major proteins of 130–145 kDa, which were tested for their insecticidal potency to four species of Lepidoptera (Helicoverpa armigera, Spodoptera exigua, S. littoralis, and S. frugiperda) and three species of mosquito (Culex pipiens pipiens, Aedes aegypti, and Anopheles stephensi). The crystal proteins were highly toxic against all the species of Lepidoptera tested, moderately toxic against two of the mosquito species (C. pipiens and Ae. aegypti), but no toxicity was observed against a third species of mosquito (An. stephensi) at the concentrations used in our study. The LC₅₀ values of the HU4‐2 Bt strain against H. armigera larvae (5.11 µg/ml) was similar to that of HD‐1 Bt strain (2.35 µg/ml), the active ingredient of the commercial product Dipel®. Additionally, the LC₅₀ values of the HU4‐2 Bt strain against S. littoralis, S. frugiperda, and S. exigua (2.64, 2.22, and 3.38 µg/ml, respectively) were also similar to that of the Bt strain isolated from the commercial product Xentari® for the same three species of Spodoptera (1.94, 1.34, and 2.19 µg/ml, respectively). Since Xentari® is significantly more toxic to Spodoptera spp. than Dipel® and, reciprocally, Dipel® is significantly more toxic against H. armigera than Xentari®, we discuss the potential of the HU4‐2 strain to control all these important lepidopteran pests.     

Interaction between crystalline proteins of two Bacillus thuringiensis strains against Spodoptera exigua

The aim of the present article was to evaluate potential synergism between crystalline proteins produced by two Bacillus thuringiensis Berliner strains, MPU B6 and MPU B9, against beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Protein inclusions of bacterial strains were isolated from a spore‐crystal mixture. We estimated the 50% lethal concentration (LC₅₀) of crystals for S. exigua larvae. Insecticidal activity of MPU B6 and MPU B9 individual crystal preparations against caterpillars were determined and compared with the commercial pesticide Foray. Protein crystals of MPU B9 had the highest toxicity against S. exigua. The proteins were approximately 25× more toxic than Foray. Insecticidal activity of protein crystals of MPU B6 isolate was approximately 2.5× higher than that of Foray. A mixture of crystals suspensions of both isolates MPU B6/MPU B9 had an additive effect on S. exigua caterpillars. The high insecticidal potency of B. thuringiensis MPU B9 crystals against S. exigua predisposes the strain for additional studies on production of a new effective preparation against pest insects.     

苏云金杆菌杀虫蛋白的多样性

苏云金杆菌是生物防治中应用最为广泛的一种杀虫剂,其杀虫蛋白具有广泛的多样性。本文就苏云金杆菌杀虫蛋白的基因、基因分布、杀虫蛋白结构以及作用机制的多样性进行了概述。     

Flocculation of Bacillus thuringiensis var. israelensis suspension and its efficacy against mosquito larvae

Bacillus thuringiensis ssp. israelensis (Bti) is increasingly used as an ecologically friendly anti-mosquito agent. The bacterium cells undergo fermentation in dilute suspensions; before practical use, therefore it is necessary to concentrate the suspensions. Aggregation by polymers is a powerful tool with which to regulate the stability of suspensions. Typically, polymers at low concentrations destabilize and at high concentrations stabilize colloidal systems. Bti suspensions can be flocculated efficiently by either cationic or anionic polyelectrolytes. Cationic polyelectolytes were found to be the most efficient flocculants for bacterial suspensions. It was shown that the degree of toxicity of the flocculated Bti suspensions for biting mosquito larvae was in the same range than in non-flocculated suspension.     

Construction of a Bacillus thuringiensis engineered strain with high toxicity and broad pesticidal spectrum against coleopteran insects

A newly engineered strain, denominated BIOT185, was constructed through integrating the cry8Ca2 gene into the endogenous plasmid of BT185 (contains cry8Ea1) by homologous recombination. The thermosensitive plasmid vector was eliminated by the rising temperature of recombinant cultures. No antibiotic gene or other unnecessary genes were introduced to the new strain. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis and Western blot analysis demonstrated that the cry8Ca2 gene was expressed normally and produced a 130-kDa protein in the BIOT185 strain. Bioassay results showed that the new strain had high toxicity to the pests Anomala corpulenta and Holotrichia parallela, which often damage the same fields.     

Characterization of spore coat proteins of Bacillus thuringiensis and Bacillus cereus

• 1.1. Spore coat extracts from Bacillus thuringiensis subspecies kurstaki and israelensis and Bacillus cereus T and B. cereus NRRL 569 were characterized by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and by amino acid analysis.
• 2.2. Both B. cereus spore coats had similar electrophoretic profiles.
• 3.3. The B. thuringiensis spore coats contained crystal proteins as major components as well as lower mol. wt proteins.
• 4.4. B. thuringiensis subsp. israelensis had a unique coat protein profile which was different from B. cereus and B. thuringiensis subsp. kurstaki coats.
• 5.5. Insecticidal activity of spores against the tobacco hornworm, Manduca sexta, and the mosquito, Aedes aegypti, also was determined.
• 6.6. B. thuringiensis subsp. kurstaki spores were lethally toxic to the tobacco hornworm (Lepidoptera) larvae, whereas spores of the other subspecies were not.
• 7.7. Except for subspecies israelensis, none of the spores was effective against the mosquito (Diptera) larvae.

     

Assessment of cone-damaging insects in a Swedish spruce seed orchard and the efficacy of large-scale application of Bacillus thuringiensis variety aizawai x kurstaki against lepidopterans

In a 2-yr study, we investigated the efficacy of large-scale application of the biological insecticide Bacillus thuringiensis variety aizawai x kurstaki (Btk) in a Swedish spruce, Picea abies L. (Karst.), seed orchard for controlling damage caused by four lepidopteran species: Dioryctria abietella Den et. Schiff. (Pyralidae), Eupithecia abietaria G?tze, E. analoga Djakonov (Geometridae), and Cydia strobilella (L.) (Tortricidae). The frequencies of these species, and Strobilomyia anthracina Czerny (Diptera: Anthomyiidae), were regularly monitored throughout the vegetative growth season to map their temporal distribution patterns and to quantify occurrences of species that may have been present in the cones at some stage during the season but migrated before the final sampling. This investigation revealed that E. abietaria occurred in similar numbers to D. abietella and has probably been overlooked as a potentially serious pest in spruce seed orchards in Sweden. To determine the number, timing, and rate of Btk required to control the lepidopterans, spraying was conducted at different phases of flowering and cone development, and three rates of Btk were applied. The Btk treatment reduced cone damage caused by D. abietella and Eupithecia spp. by one-half in 2002, a year with an intermediate number of cones, but the effect was weaker in 2003, when the cone crop was low. Damage caused by C. strobilella was not affected by the treatment. The different rates of Btk application did not affect the results, and repeated spraying seemed to be effective during 2002 but not in 2003.     

Control efficacy of Bacillus thuringiensis and a new granulovirus isolate against Cydia pomonella in orchards

Abstract

Codling moth, Cydia pomonella, is one of the most serious pests of apple and pear worldwide. This study evaluates the efficacies of a granulovirus, a Bacillus thuringiensis (Bt) strain and their combination in the control of C. pomonella in China. A Cydia pomonella granulovirus (CpGV) was isolated from C. pomonella cadavers in an orchard in Gansu, China. Droplet-feeding bioassays showed the median lethal concentration (LC₅₀) of this CpGV isolate (CpGV-C1) against the third instar C. pomonella larvae was 770 OBs µl^?1. The LC₅₀ values of Bt C-33 and kurstaki HD-1 against the third instar larvae were 26.3 µg ml^?1 and 15.7 µg ml^?1, respectively. Field tests indicated the control efficacies of CpGV-C1 and the combination of CpGV-C1 and Bt against C. pomonella larvae in apple orchards were similar to that of beta-cypermethrin. Our data demonstrated that the combination of CpGV and Bt might effectively protect apple fruits from the damage of C. pomonella larvae and had the potential to be developed as a low-cost, highly effective insecticide.     

Using worms to better understand how Bacillus thuringiensis kills insects

Bacillus thuringiensis is widely used as a biological pesticide to control insects that either cause damage to crops or transmit disease. That it can also target the model organism Caenorhabditis elegans has not only provided exciting new insights into how the toxins produced by the bacterium target their victims but also how target insects counter the attack. Modern approaches such as reverse genetics and microarray technology have revealed novel receptors for the toxins and possible signal transduction pathways induced within the host following intoxication. This article will discuss how these findings fit in with current models and how they might influence future studies.