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PubMed1987

Nucleotide sequence of the insecticidal protein gene of Bacillus thuringiensis strain aizawai IPL7 and its high-level expression in Escherichia coli.

A DNA fragment carrying the insecticidal protein gene of Bacillus thuringiensis subsp. aizawai IPL7 was cloned from a 78-kb plasmid. The nucleotide sequence revealed that the cloned DNA fragment contained a 3465-bp protein-coding region with 156-bp 5'-flanking, and 168-bp 3'-flanking regions. The open reading frame encoded a 130,690 Da protein consisting of 1155 amino acid residues. Nucleotide sequence comparison of the aizawai gene with the published berliner 1715 gene showed only 8 nt changes in the coding regions. It was found that 72 bp of the 5'-flanking sequence of the cloned aizawai gene was responsible for constitutive expression of the 130-kDa protein gene in Escherichia coli. The expression was greatly enhanced by introducing the tac promoter upstream from the 72-bp 5'-flanking region of the aizawai gene. Under optimal conditions, the 130-kDa insecticidal protein amounted to 38% of the total cellular protein.

Amino Acid Sequence↗
PubMed2006

Toxicity of Bacillus thuringiensis delta-endotoxins against bean shoot borer (Epinotia aporema Wals.) larvae, a major soybean pest in Argentina.

The toxicity of seven Bacillus thuringiensis Cry protoxins was tested against neonate larvae of Epinotia aporema, a major soybean pest in Argentina and South America. The most active protoxins were Cry1Ab and Cry1Ac, with LC50 values of 0.55 and 1.39 microg/ml, respectively. Cry1Aa, Cry1Ba, Cry1Ca, and Cry9Ca protoxins were equally toxic with LC50 values about 4 microg/ml, whereas Cry1Da was not toxic. The synergistic activity of different protoxin-mixtures was also analyzed, no synergistic effect between the Cry proteins was observed, with the exception of the poorly toxic Cry1Ba/Cry1Da mixture that was slightly synergistic. The binding capacity of individual Cry1 and Cry9Ca toxins to brush border membranes of E. aporema was also determined. The non-toxic Cry1Da toxin was the only toxin unable to bind to E. aporema membranes. In addition the heterologous competition experiments showed that Cry1Ab and Cry1Ac toxins share a common binding site. Based on these data, we propose that Cry1Ab and Cry1Ac toxins could be used in the biological control of E. aporema.

Animals↗
PubMed1998

Video imaging analysis of the plasma membrane permeabilizing effects of Bacillus thuringiensis insecticidal toxins in Sf9 cells.

The size and ionic selectivity of the pores formed by the insecticidal crystal protein Cry1C from Bacillus thuringiensis in the plasma membrane of Sf9 cells, an established cell line derived from the fall armyworm Spodoptera frugiperda, were analyzed with a video imaging technique. Changes in the permeability of the membrane were estimated from the rate of osmotic swelling of the cells. In the presence of Cry1C, which is toxic to Sf9 cells, the permeability of the cell membrane to KCl and glucose increased in a dose-dependent manner. In contrast, Cry1Aa, Cry1Ab and Cry1Ac, toxins to which Sf9 cells are not susceptible, had no detectable effect. Pores formed by Cry1C allowed the diffusion of sucrose, but were impermeable to the trisaccharide raffinose. On the basis of the hydrodynamic radii of these substances, the diameter of the pores was estimated to be 1.0-1.2 nm. In the presence of salts, the rate of swelling of cells exposed to Cry1C was about equally influenced by the size of the anion as by that of the cation, indicating that the ionic selectivity of the pores is low.

Animals↗
PubMed2001

Entomopathogenic activities of environmental isolates of Bacillus thuringiensis against dipteran larvae.

Twenty-five field isolates of Bacillus thuringiensis from the Lower Silesia region of Poland, the Osola plain, and phylloplane niches and soil samples from the Karkonosze National Park were tested for insecticidal activity against larvae of the dipterans Aedes aegypti, Drosophila melanogaster and Musca domestica. The spore-crystal mixture of B. thuringiensis finitimus (soil isolate) killed nearly half of the fourth instar larvae of Ae. aegypti. Similar mortality of between 39-61% was recorded after treatment with two phylloplane isolates belonging to biochemical type I of B. thuringiensis (subsp. japonensis, yoso and jinghongiensis) and type IV (subsp. tochigiensis,). The effect of B. thuringiensis wratislaviensis H-47 was lowest, with larval mortality ranging from 7-28%. The susceptibility of D. melanogaster, evaluated as percentage of larvae that did not survive to adulthood, varied between 0-38% and 0-45% at dosages of 0.5 and 1 ml, respectively. The LC50s ranged from 5.07 x 10(9) to 1.04 x 10(11) spore-crystal mixture. The LC50s for M. domestica larvae were 4.1-4.8 x 10(8) spores/ml of B. thuringiensis finitimus and the phylloplane strain KpC1 (I type) and 2.9 x 10(9) for the phyloplane representative of group I. Generally, all tested isolates showed the most activity against common fly larvae. The highest (64-81% mortality) was observed after treatment with both phylloplane (OpPs1, KpF3, KpC1) and soil isolates (KsAc1) of biochemical type I as well as B. thuringiensis finitimus (type III).

Aedes↗
PubMed2004

Role of toxin activation on binding and pore formation activity of the Bacillus thuringiensis Cry3 toxins in membranes of Leptinotarsa decemlineata (Say).

Binding and pore formation constitute key steps in the mode of action of Bacillus thuringiensis delta-endotoxins. In this work, we present a comparative analysis of toxin-binding capacities of proteolytically processed Cry3A, Cry3B and Cry3C toxins to brush border membranes (BBMV) of the Colorado potato beetle Leptinotarsa decemlineata (CPB), a major potato coleopteran-insect pest. Competition experiments showed that the three Cry3 proteolytically activated toxins share a common binding site. Also heterologous competition experiments showed that Cry3Aa and Cry3Ca toxins have an extra binding site that is not shared with Cry3Ba toxin. The pore formation activity of the three different Cry3 toxins is analysed. High pore-formation activities were observed in Cry3 toxins obtained by proteolytical activation with CPB BBMV in contrast to toxins activated with either trypsin or chymotrypsin proteases. The pore-formation activity correlated with the formation of soluble oligomeric structures. Our data support that, similarly to the Cry1A toxins, the Cry3 oligomer is formed after receptor binding and before membrane insertion, forming a pre-pore structure that is insertion-competent.

Animals↗
PubMed2002

Comparison of Bacillus thuringiensis corn hybrids and insecticide-treated isolines exposed to bivoltine European corn borer (Lepidoptera: Crambidae) in South Dakota.

The performances of Bacillus thuringiensis (Bt) corn hybrids and permethrin-treated isolines were evaluated in South Dakota from 1997 to 1999. The corn hybrids were exposed to natural seasonal fluctuations of a bivoltine ecotype European corn borer population. Larval injury parameters, grain yields, and gross incomes were quantified during the 3-yr study. The use of either Bt hybrids or whorl-applied permethrin granules resulted in significant yield advantages in only 1 out of 3 yr of performance testing. Under high corn borer pressure in 1997, the performances of the Bt corn hybrids and permethrin-treated isolines were similar, and significantly better than the untreated isolines. However, injury-free corn did not necessarily translate into higher yields in some of the hybrid groups. Grain moisture at harvest, which can result in moisture penalty or dockage, was significantly higher in some Bt corn hybrids. Neither the Bt hybrids nor the permethrin-treated isolines produced significant advantages in yields in 1998 and 1999 when infestations of first-generation corn borer were almost nonexistent and infestations of second-generation European corn borers were moderate.

Animals↗
PubMed2005

Occurrence and significance of Bacillus cereus and Bacillus thuringiensis in ready-to-eat food.

Among 48,901 samples of ready-to-eat food products at the Danish retail market, 0.5% had counts of Bacillus cereus-like bacteria above 10(4) cfu g(-1). The high counts were most frequently found in starchy, cooked products, but also in fresh cucumbers and tomatoes. Forty randomly selected strains had at least one gene or component involved in human diarrhoeal disease, while emetic toxin was related to only one B. cereus strain. A new observation was that 31 out of the 40 randomly selected B. cereus-like strains could be classified as Bacillus thuringiensis due to crystal production and/or content of cry genes. Thus, a large proportion of the B. cereus-like organisms present in food may belong to B. thuringiensis.

Bacillus cereus↗
PubMed1990

A novel Bacillus thuringiensis gene encoding a Spodoptera exigua-specific crystal protein.

Only one of the four lepidoptera-specific crystal protein subclasses (CryIC) Bacillus thuringiensis was previously shown to be highly toxic against several Spodoptera species. By using a cryIC-derived nucleotide probe, DNA from 25 different strains of B. thuringiensis was screened for the presence of homologous sequences. A putative crystal protein gene, considerably different from the cryIC gene subclass, was identified in the DNA of strain 4F1 (serotype kenyae) and cloned in Escherichia coli. Its nucleotide sequence was determined and appeared to contain several features typical for a crystal protein gene. Furthermore, the region coding for the N-terminal part of the putative toxic fragment showed extensive homology to subclass cryIA sequences derived from gene BtII, whereas the region coding for the C-terminal part appeared to be highly homologous to the cryIC gene BtVI. With an anti-crystal protein antiserum, a polypeptide of the expected size could be demonstrated in Western immunoblots, onto which a lysate of E. coli cells harboring the putative gene, now designated as BtXI, had been transferred. Cells expressing the gene appeared to be equally toxic against larvae of Spodoptera exigua as recombinant cells expressing the BtVI (cryIC)-encoded crystal protein. However, no toxicity against larvae of Heliothis virescens, Mamestra brassicae, or Pieris brassicae could be demonstrated. The nucleotide sequence analysis and the toxicity studies showed that this novel crystal protein gene falls into a new cryl gene subclass. We propose that this subclass be referred to as cryIE.

Amino Acid Sequence↗
PubMed2006

The compatibility of a nucleopolyhedrosis virus control with resistance management for Bacillus thuringiensis: co-infection and cross-resistance studies with the diamondback moth, Plutella xylostella.

The use of genetically modified crops expressing Bacillus thuringiensis (Bt) toxins can lead to the reduction in application of broad-spectrum pesticides and an increased opportunity for supplementary biological control. Bt microbial sprays are also used by organic growers or as part of integrated pest management programs that rely on the use of natural enemies. In both applications the evolution of resistance to Bt toxins is a potential problem. Natural enemies (pathogens or insects) acting in combination with toxins can accelerate or decelerate the evolution of resistance to Bt. In the present study we investigated whether the use of a nucleopolyhedrovirus (AcMNPV) could potentially affect the evolution of resistance to the Bt toxin Cry1Ac in Plutella xylostella. At low toxin doses there was evidence for antagonistic interactions between AcMNPV and Cry1Ac resistant and susceptible insects. However, this antagonism was much stronger and more widespread for susceptible larvae; interactions were generally not distinguishable from additive for resistant larvae. Selection for resistance to Cry1Ac in two populations of P. xylostella with differing resistance mechanisms did not produce any correlated changes in resistance to AcMNPV. Stronger antagonistic interactions between Bt and AcMNPV on susceptible rather than resistant larvae can decrease the relative fitness between Bt-resistant and susceptible larvae. These interactions and the lack of cross-resistance between virus and toxin suggest that the use of NPV is compatible with resistance management to Bt products.

Animals↗
PubMed2006

Decreased whorl and ear damage in nine mon810 Bacillus thuringiensis (Bt)-transgenic corn hybrids compared with their non-Bt counterparts.

We examined nine pairs of near-isogenic hybrids of Bacillus thuringiensis (Bt) and non-Bt corn, Zea mays L., at two locations in 1999 and three locations in 2000 to compare the effects of Bt toxins on damage caused by Helicoverpa zea (Boddie) to whorl stage field corn, and ear damage at harvest, as well as yield. We found that whorl damage was less in all Bt hybrids compared with their non-Bt counterparts each year and at each location. Differences in ear damage between Bt and non-Bt hybrids, however, differed in 1999 and 2000. In 1999, only one Bt hybrid, NC+5788Bt, had less ear damage than its non-Bt counterpart at the dryland site, whereas four Bt hybrids, C8120Bt, P31B13Bt, P33VO8Bt, and NC+5788Bt, had less damage at the irrigated site. In 2000, most Bt hybrids had less ear damage than their non-Bt counterparts at each location. Differences in whorl damage did not translate into yield differences. However, variations in ear damage were partially reflected in yield differences. In 1999, P31B13Bt and P33V08Bt had higher yields than their non-Bt counterparts at both sites, whereas in 2000 all Bt hybrids had higher yields. Also, although whorl damage was not correlated with yield, ear damage was negatively correlated with yield; increasing ear damage by H. zea decreased yield for Bt and non-Bt hybrids alike. Overall, depending on location and year, each centimeter of H. zea ear damage reduced yield by between 2 and 13%.

Animals↗
PubMed1996

Membrane permeabilization induced by cytolytic delta-endotoxin CytA from Bacillus thuringiensis var. israelensis.

CytA is a member of a functionally defined family of insecticidal delta-endotoxins occurring in parasporal crystals of Bacillus thuringiensis var. israelensis. We investigated the ability of CytA to permeabilize the membrane and release fluorescence marker molecules from unilamellar lipid vesicles. Both protoxin (27 kDa) and proteolytically activated toxin (24 kDa) were very effective in permeabilization of unilamellar lipid vesicles: concentrations as low as several nanomolar produced a significant effect. The toxin was about 2-3 times more effective than the protoxin. The concentration of CytA required for the same extent of calcein release in large unilamellar vesicles (LUV) was 5-10 times lower than that in small unilamellar vesicles (SUV). Both small (calcein) and large (fluorescein-dextrans, MW 3000 and 10 000) molecules were released from the vesicles by CytA with comparable single-exponential kinetics. The release was an all-or-none event, i.e., each vesicle either released all of its contents or remained completely intact. Binding of CytA to lipid membranes did not show appreciable cooperativity, the apparent binding constant (Kapp) being on the order of 10(5) M-1. The plots of kinetics of release vs bound protein/ lipid ratio and the differential effects of CytA on LUV vs SUV indicate that at least 140 toxin molecules or 311 protoxin molecules must bind to an LUV before the latter starts losing its integrity. The necessity of adsorption of this relatively large number of toxin molecules to trigger permeabilization, together with the lack of discrimination in the size of the released marker molecules, suggests that the effect of CytA is a general, detergent-like, perturbation of the membrane rather than creation of small, well-defined, proteinaceous channels.

Bacillus thuringiensis↗
PubMed1994

A mixture of Manduca sexta aminopeptidase and phosphatase enhances Bacillus thuringiensis insecticidal CryIA(c) toxin binding and 86Rb(+)-K+ efflux in vitro.

CryIA(c) delta-endotoxin, a member of the CryI family of Bacillus thuringiensis insecticidal proteins, specifically recognizes and binds with high affinity to target proteins in the midgut of susceptible insects. Protein blots of Manduca sexta brush-border membranes probed with 125I-CryIA(c) identify a major binding protein of 120 kDa and a minor binding protein of 65 kDa. Monoclonal antibodies were raised against the 120-kDa toxin binding protein. Using isoelectric focusing and monoclonal antibodies (2B3, 8G1, and 12B8) 120- and 65-kDa brush-border proteins were isolated. Labeled CryIA(c) and monoclonal antibodies probed to blots of the affinity-selected proteins recognized the 120- and 65-kDa proteins. When reconstituted into phospholipid vesicles, antibody-selected proteins increased toxin binding (35%) and enhanced toxin-induced 86Rb+ release up to 1000-fold. The 120-kDa protein was identified as aminopeptidase N (EC 3.4.11.2). A CryIA(c)-sensitive phosphatase was also present in the 120/65-kDa protein mixture. These findings provide the first identification of B. thuringiensis toxin binding proteins, although confirmation is needed in vivo.

Amino Acid Sequence↗
PubMed2001

Isolation of Bacillus thuringiensis from intertidal brackish sediments in mangroves.

Intertidal brackish sediments in mangroves were examined for isolation of Bacillus thuringiensis strains with novel toxicity spectra. A total of 18 B. thuringiensis isolates were recovered from eight sediment samples (36.4%) out of 22 samples tested. The frequency of B. thuringiensis was 1.3% among the colonies of Bacillus cereus/B. thuringiensis group. While five isolates were allocated to the four H serogroups, the majority of the isolates were serologically untypable or untestable. Two isolates belonging to the serovar israelensis/tochigiensis (H14/19) exhibited strong toxicities against larvae of the mosquito, Culex pipiens molestus, and mammalian cells (sheep erythrocyte and two human cancer cell lines) in vitro. The other 16 isolates showed no toxicity against the mosquito and mammalian cells. None of the isolates showed larvicidal activity against the diamondback moth, Plutella xylostella. Strong lectin activities against sheep erythrocytes were associated with two serologically untestable isolates and an H3 isolate.

Animals↗
PubMedDate not supplied

Determination of exotoxin in Bacillus thuringiensis cells.

The presence of exotoxin in Bacillus thuringiensis was demonstrated and its quantity in the cells determined. The concentration of exotoxin in the producing microorganism is approximately half the concentration of ATP. Exotoxin is produced at such a rate that the cell excretes 1/5 to 1/4 of its exotoxin content into the medium per minute.

Adenosine Triphosphate↗
PubMed2005

Screening of cry2 genes in Bacillus thuringiensis isolates from Argentina.

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for identification of cry2 genes from Bacillus thuringiensis (Bt) was established. Strains from different sources of Argentina were analyzed to study the distribution of cry2 genes. The results showed that cry2Aa/cry2Ab profile was the most abundant irrespective of source and represented 56 of 59 Bt isolates (94.9%). Three different cry2 profiles were found in this collection, one of which was novel.

Animals↗
PubMed2002

Extent of variation of the Bacillus thuringiensis toxin reservoir: the case of the geranium bronze, Cacyreus marshalli butler (Lepidoptera: Lycaenidae).

Despite the fact that around 200 cry genes from Bacillus thuringiensis have already been cloned, only a few Cry proteins are toxic towards a given pest. A crucial step in the mode of action of Cry proteins is binding to specific sites in the midgut of susceptible insects. Binding studies in insects that have developed cross-resistance discourage the combined use of Cry proteins sharing the same binding site. If resistance management strategies are to be implemented, the arsenal of Cry proteins suitable to control a given pest may be not so vast as it might seem at first. The present study evaluates the potential of B. thuringiensis for the control of a new pest, the geranium bronze (Cacyreus marshalli Butler), a butterfly that is threatening the popularity of geraniums in Spain. Eleven of the most common Cry proteins from the three lepidopteran-active Cry families (Cry1, Cry2, and Cry9) were tested against the geranium bronze for their toxicity and binding site relationships. Using 125I-labeled Cry1A proteins we found that, of the seven most active Cry proteins, six competed for binding to the same site. For the long-term control of the geranium bronze with B. thuringiensis-based insecticides it would be advisable to combine any of the Cry proteins sharing the binding site (preferably Cry1Ab, since it is the most toxic) with those not competing for the same site. Cry1Ba would be the best choice of these proteins, since it is significantly more toxic than the others not binding to the common site.

Animals↗
PubMed1993

Insect resistant rice generated by introduction of a modified delta-endotoxin gene of Bacillus thuringiensis.

As a first step towards development of insect resistant rice we have introduced a truncated delta-endotoxin gene, cryIA(b) of Bacillus thuringiensis (B.t.) which has specific biological activity against lepidopteran insects into a japonica rice. To highly express the cryIA(b) gene in rice the coding sequence was extensively modified based on the codon usage of rice genes. Transgenic plants efficiently expressed the modified cryIA(b) gene at both mRNA and protein levels. Bioassays using R2 generation plants with two major rice insect pests, striped stemborer (Chilo suppressalis) and leaffolder (Cnaphalocrosis medinalis), indicated that transgenic rice plants expressing the CryIA(b) protein are more resistant to these pests than untransformed control plants. Our results suggest that the B.t. endotoxin genes will be useful for the rational development of new rice varieties resistant to major insect pests.

Amino Acid Sequence↗
PubMed2002

Larvicidal toxins from Bacillus thuringiensis subspp. kurstaki, morrisoni (strain tenebrionis), and israelensis have no microbicidal or microbiostatic activity against selected bacteria, fungi, and algae in vitro.

The insecticidal toxins from Bacillus thuringiensis subspp. kurstaki (antilepidopteran), morrisoni strain tenebrionis (anticoleopteran), and israelensis (antidipteran) did not affect the growth of a variety of bacteria (8 gram-negative, 5 gram-positive, and a cyanobacterium), fungi (2 Zygomycetes, 1 Ascomycete, 2 Deuteromycetes, and 2 yeasts), and algae (primarily green and diatoms) in pure and mixed culture, as determined by dilution, disk-diffusion, and sporulation assays with purified free and clay-bound toxins. The insecticidal crystal proteins from B. thuringiensis subspp. kurstaki and israelensis had no antibiotic effect on various gram-positive bacteria.

Animals↗