Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Bacillus thuringiensis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed2004

Cloning and nucleotide sequence of a novel cry gene from Bacillus thuringiensis.

A cry1Ab-type gene was cloned from a new isolate of Bacillus thuringiensis by PCR. When restriction pattern was compared with that of known genes it was found to have additional restriction site for ClaI. Nucleotide sequencing and homology search revealed that the toxin shared 95% homology with the known Cry1Ab proteins as compared to more than 98% homology among the other reported Cry1Ab toxins. The gene encoded a sequence of 1,177 amino acids compared to 1,155 amino acids encoded by all the other 16 cry1Ab genes reported so far. An additional stretch of 22 amino acids after the amino acid G793 in the new toxin sequence showed 100% homology with several other cry genes within cry1 family. Homology search indicated that the new cry1Ab-type gene might have resulted by nucleotide rearrangement between cry1Ab and cry1Aa/cry1Ac genes.

Bacillus thuringiensis↗
PubMedDate not supplied

[The choice of the optimal aeration conditions for the stab cultivation of Bacillus thuringiensis H14 266/2-1].

Optimal conditions of aeration with depth regime of cultivation of Bacillus thuringiensis H14 266/2-1, their effect on the output of biomass, endotoxin and activity of bacteria have been studied. The aeration conditions are optimized using the mathematical method of experiment planning. It is established that the air supply favours an increase of the bacillary biomass and insecticide activity for the whole cultivation period. In the first day of fermentation it is inexpedient to increase to rate of the medium agitation. To obtain a high titre of cells of the studied bacilli and to retain their activity a specific air consumption is recommended amounting to 0.5 1/1/min for the first 12h with an increase to 1.01/1/min in the following hours of fermentation, the constant rate of the medium agitation being 500 rev/min.

Aedes↗
PubMed2000

Cry1Ac protoxin from Bacillus thuringiensis sp. kurstaki HD73 binds to surface proteins in the mouse small intestine.

Bacillus thuringiensis (Bt), considered a safe insecticide, produces insecticidal proteins named Cry during sporulation, which possess exceptional immunological properties. In this work using an immunohistochemical test we demonstrated that Cry1Ac protoxin (pCry1Ac) binds to the mucosal surface of the mouse small intestine. Ligand blot assay allowed us to detect, under denaturing conditions, six pCry1Ac-binding polypeptides present in brush border membrane vesicles isolated from the small intestine. Moreover, this protein induced in situ temporal changes in the electrophysiological properties of the mouse jejunum. The data obtained indicate a possible interaction in vivo of Cry proteins with the animal bowel which could induce changes in the physiological status of the intestine.

Animals↗
PubMed2002

Resistance monitoring of Helicoverpa armigera (Lepidoptera Noctuidae) to Bacillus thuringiensis insecticidal protein in China.

Sensitivities of Helicoverpa armigera (Hübner) field populations to Bacillus thuringiensis (Bt) insecticidal protein CrylAc were monitored during 1998-2000 in China. A total of 41 strains was sampled, and most of them were collected from Bt cotton planting regions. The range of IC50 values (concentration producing 50% inhibition of larval development to third instar) among different populations in 1998,1999, and 2000 were 0.020-0.105 microg/ml, 0.016-0.099 microg/ml, and 0.016-0.080 microg/ml, respectively. Diagnostic concentration studies (IC99) showed that the percentage of individuals reaching third instar ranged from 0 to 4.35%, with only eight of the 41 tested populations showing values above 0%. Also interesting was a trend over successive years in which fewer populations contained individuals that survived the diagnostic concentration by reaching third instar. Considering these data, it was determined that the field populations sampled during the 3-yr study were susceptible to CrylAc protein, and that movement toward resistance among H. armigera populations was not apparent.

Animals↗
PubMed2002

Isolation and characterization of a strain of Bacillus thuringiensis ssp. kurstaki containing a new delta-endotoxin gene.

A strain of Bacillus thuringiensis that showed significantly high toxicity to Plutella xylostella and Spodoptera exigua was isolated from a Korean soil sample and characterized. The isolate, named B. thuringiensis K1, was determined to belong to ssp. kurstaki (H3a3b3c) type by an H antisera agglutination test and produced bipyramidal inclusions. Plasmid pattern of K1 was different from that of the reference strain, ssp. kurstaki HD-1, but the parasporal inclusion protein profile of K1 had two major bands that were similar in size to those of ssp. kurstaki HD-1. To verify the delta-endotoxin gene types of K1, PCR analysis with specific cry gene primers was performed to show that K1 contained a new cry gene in addition to cry1Aa, cry1Ab, cry1Ac, cry1E and cry2 genes. PCR-amplified region of the new cry gene, cryX, showed 79% similarity to cry1Fa1 gene (GenBank Accession No. M63897). In an insect toxicity assay, K1 had higher toxicity against Plutella xylostella and S. exigua than ssp. kurstaki HD-1.

Animals↗
PubMed1994

Protozoan-enhanced toxicity of Bacillus thuringiensis var. israelensis delta-endotoxin against Aedes aegypti larvae.

The toxicity of Bacillus thuringiensis var. israelensis (Bti) in mosquito larvae was enhanced by encapsulation in the protozoan Tetrahymena pyriformis. Aedes aegypti larvae which fed on T. pyriformis loaded with Bti died about three times faster than when fed on the same concentrations of Bti alone due to ingestion of higher toxin concentrations, reflected by shorter death times of exposed populations. The best larvicidal activities were achieved at ratios of cell/spore numbers in the range of 1:200 to 1:500. This enhancement of mortality by preincubation with T. pyriformis was higher at low Bti concentrations or in late third-instar larvae. Ninety minutes of preincubation yielded the best enhancement effect. Toxicity enhancement is very likely a consequence of concentrating large quantities of Bti spores and crystals (containing delta-endotoxin) by T. pyriformis cells and delivering them to the larvae. Shortening larval mortality time by encapsulation in T. pyriformis should reduce the exposure time of Bti to unfavorable field conditions that inactivate its larvicidal activity. Whether this method will indeed improve Bti efficacy is still to be determined.

Aedes↗
PubMed2000

Evidence for intermolecular interaction as a necessary step for pore-formation activity and toxicity of Bacillus thuringiensis Cry1Ab toxin.

Based on the observation of large conductance states formed by Bacillus thuringiensis Cry toxins in synthetic planar lipid bilayers and the estimation of a pore size of 10-20 A, it has been proposed that the pore could be formed by an oligomer containing four to six Cry toxin monomers. However, there is a lack of information regarding the insertion of Cry toxins into the membrane and oligomer formation. Here we provide direct evidence showing that the intermolecular interaction between Cry1Ab toxin monomers is a necessary step for pore formation and toxicity. Two Cry1Ab mutant proteins affected in different steps of their mode of action (F371A in receptor binding and H168F in pore formation) were affected in toxicity against Manduca sexta larvae. Binding analysis showed that F371A protein bound more efficiently to M. sexta brush border membrane vesicles when mixed with H168F in a one to one ratio. These mutant proteins also recovered pore-formation activity, measured with a fluorescent dye with isolated brush border membrane vesicles, and toxicity against M. sexta larvae when mixed, showing that monomers affected in different steps of their mode of action can form functional hetero-oligomers.

Animals↗
PubMed2000

Bivalent sequential binding model of a Bacillus thuringiensis toxin to gypsy moth aminopeptidase N receptor.

Specificity for target insects of Bacillus thuringiensis insecticidal Cry toxins is largely determined by toxin affinity for insect midgut receptors. The mode of binding for one such toxin-receptor complex was investigated by extensive toxin mutagenesis, followed by real-time receptor binding analysis using an optical biosensor (BIAcore). Wild-type Cry1Ac, a three-domain, lepidopteran-specific toxin, bound purified gypsy moth (Lymantria dispar) aminopeptidase N (APN) biphasically. Site 1 displayed fast association and dissociation kinetics, while site 2 possessed slower kinetics, yet tighter affinity. We empirically determined that two Cry1Ac surface regions are involved in in vivo toxicity and APN binding. Mutations within domain III affected binding rates to APN site 1, whereas mutations in domain II affected binding rates to APN site 2. Furthermore, domain III contact is completely inhibited in the presence of N-acetylgalactosamine, indicating loss of domain III binding eliminates all APN binding. Based upon these observations, the following model is proposed. A cavity in lectin-like domain III initiates docking through recognition of an N-acetylgalactosamine moiety on L. dispar APN. Following primary docking, a higher affinity domain II binding mechanism occurs, which is critical for insecticidal activity.

Animals↗
PubMed1993

Insect-resistant chrysanthemum calluses by introduction of a Bacillus thuringiensis crystal protein gene.

A 3'-end truncated crystal protein gene, derived from Bacillus thuringiensis (Bt) subsp. aizawai 7.21, encoding the toxic fragment of the insecticidal protein cryIA(b), was constructed. The gene was inserted into a transformation vector, also carrying the neomycin phosphotransferase II (nptII) gene and the beta-glucuronidase (gus) gene, and introduced in the oncogenic Agrobacterium tumefaciens strain A281, harbouring the Ti-plasmid pTiBO542. The recombinant Agrobacterium strain was used to transform leaf explants of chrysanthemum (Dendranthema grandiflora) cultivar Parliament. The resulting tumours were kanamycin-resistant, exhibited beta-glucuronidase activity and produced agropine and mannopine. In most tumours, all simultaneously transferred genes were expressed, owing to selection for the presence of both T-DNAs, but no correlation was found between the level of expression of the various genes. A bioassay was developed, in which larvae were fed with tumorous chrysanthemum tissue, in order to detect the effect of the transferred toxin gene on larval development. Using this bioassay with second instar larvae of Heliothis virescens (tobacco budworm), 17 tumour lines were tested. Several of these lines proved to be strongly inhibitory to larval growth. These results indicate that Bt-based insect resistance might be used as a tool in reducing the amount of pesticides used in chrysanthemum culture.

Agrobacterium tumefaciens↗
PubMed1992

Novel Bacillus thuringiensis insecticidal crystal protein with a silent activity against coleopteran larvae.

A novel Bacillus thuringiensis crystal protein with a silent activity against the Colorado potato beetle is described. The crystal proteins are produced as bipyramidal crystals. These crystals contain a protein of 129 kDa with a trypsin-resistant core fragment of 72 kDa. Neither a spore-crystal mixture nor in vitro-solubilized crystals are toxic to any of several Lepidoptera and Coleoptera species tested. In contrast, a trypsin-treated solution containing the 72-kDa tryptic core fragment of the protoxin is highly toxic to Colorado potato beetle larvae. The crystal protein-encoding gene was cloned and sequenced. The inferred amino acid sequence of the putative toxic fragment has 37, 32, and 33% homology to the CryIIIA, CryIIIB, and CryIIID toxins, respectively. Interestingly, the 501 C-terminal amino acids show 41 to 48% amino acid identity with corresponding C-terminal amino acid sequences of other crystal proteins. Because of the toxicity of the fragment to the Colorado potato beetle and because of the distinct similarities of the toxic fragment with the other CryIII proteins, this gene was given a new subclass name (cryIIIC) within the CryIII class of coleopteran-active crystal proteins. CryIIIC represents the first example of a crystal protein with a silent activity towards coleopteran insect larvae. Natural CryIIIC crystals are not toxic. Toxicity is revealed only after an in vitro solubilization and activation step.

Amino Acid Sequence↗
PubMed2002

Altered Glycosylation of 63- and 68-kilodalton microvillar proteins in Heliothis virescens correlates with reduced Cry1 toxin binding, decreased pore formation, and increased resistance to Bacillus thuringiensis Cry1 toxins.

The binding and pore formation abilities of Cry1A and Cry1Fa Bacillus thuringiensis toxins were analyzed by using brush border membrane vesicles (BBMV) prepared from sensitive (YDK) and resistant (YHD2) strains of Heliothis virescens. 125I-labeled Cry1Aa, Cry1Ab, and Cry1Ac toxins did not bind to BBMV from the resistant YHD2 strain, while specific binding to sensitive YDK vesicles was observed. Binding assays revealed a reduction in Cry1Fa binding to BBMV from resistant larvae compared to Cry1Fa binding to BBMV from sensitive larvae. In agreement with this reduction in binding, neither Cry1A nor Cry1Fa toxin altered the permeability of membrane vesicles from resistant larvae, as measured by a light-scattering assay. Ligand blotting experiments performed with BBMV and 125I-Cry1Ac did not differentiate sensitive larvae from resistant larvae. Iodination of BBMV surface proteins suggested that putative toxin-binding proteins were exposed on the surface of the BBMV from resistant insects. BBMV protein blots probed with the N-acetylgalactosamine-specific lectin soybean agglutinin (SBA) revealed altered glycosylation of 63- and 68-kDa glycoproteins but not altered glycosylation of known Cry1 toxin-binding proteins in YHD2 BBMV. The F1 progeny of crosses between sensitive and resistant insects were similar to the sensitive strain when they were tested by toxin-binding assays, light-scattering assays, and lectin blotting with SBA. These results are evidence that a dramatic reduction in toxin binding is responsible for the increased resistance and cross-resistance to Cry1 toxins observed in the YHD2 strain of H. virescens and that this trait correlates with altered glycosylation of specific brush border membrane glycoproteins.

Animals↗
PubMed1999

Biochemical characterization of Bacillus thuringiensis cytolytic toxins in association with a phospholipid bilayer.

The interaction of two Bacillus thuringiensis cytolytic toxins, CytA and CytB, with a phospholipid bilayer and their structure in the membrane-bound state were investigated by proteolysis using phospholipid vesicles as a model system. A toxin conformational change upon membrane binding was detected by comparing the proteolytic profile of membrane-bound toxin and saline-solubilized toxin. When membrane-bound toxin was exposed to protease K or trypsin, novel cleavage sites were found between the alpha-helical N-terminal half and beta-strand C-terminal half of the structure at K154 and N155 in CytA and at I150 and G141 in CytB. N-terminal sequencing of membrane-protected fragments showed that the C-terminal half of the toxin structure comprising mainly beta-strands was inserted into the membrane, whereas the N-terminal half comprising mainly alpha-helices was exposed on the outside of the liposomes and could be removed when liposomes with bound toxin were washed extensively after proteolysis. The C-termini of the membrane-inserted proteolytic fragments were also located by a combination of N-terminal sequencing and measurement of the molecular masses of the fragments by electrospray MS. Using a liposome glucose-release assay, the membrane-inserted structure was seen to retain its function as a membrane pore even after removal of exposed N-terminal segments by proteolysis. These data strongly suggest that the pores for glucose release are assembled from the three major beta-strands (beta-5, beta-6 and beta-7) in the C-terminal half of the toxin.

Amino Acid Sequence↗
PubMed2001

A phylogenetic analysis of Bacillus thuringiensis serovars by RFLP-based ribotyping.

AIMS: To determine the 23S and 5S rRNA gene fingerprints in order to reveal phylogenetic relationships among Bacillus thuringiensis strains. METHODS AND RESULTS: Eighty-six B. thuringiensis strains which include 80 serovar type strains, five intraserovar strains and a non-serotypeable strain, wuhanensis, were tested. Total DNA was digested with EcoRI and HindIII. The 23S and 5S rRNA gene restriction fragment length polymorphisms showed 82 distinctive ribopatterns. The dendrogram generated by numerical analysis showed 10 phylogenetic groups and six ungrouped serovars at the 95.5% DNA relatedness rate. A second dendrogram was constructed using a combination of the data from this study and from a previous study on 16S rRNA gene fingerprinting. It revealed eight distinct phylogenetic groups and three ungrouped serovars at the 94% DNA relatedness rate. CONCLUSION: This method permitted the classification and positioning of a wide variety of B. thuringiensis strains on a phylogenetic tree. Bacillus thuringiensis strains appear to be relatively homogeneous and to share a high degree of DNA relatedness. SIGNIFICANCE AND IMPACT OF THE STUDY: This study contributes a further step to the definition of valid taxonomic sublevels for the B. thuringiensis species.

Bacillus thuringiensis↗
PubMed1995

Regulation of insecticidal crystal protein production in Bacillus thuringiensis.

The production of insecticidal crystal proteins (ICPs) in Bacillus thuringiensis normally coincides with sporulation, resulting in the appearance of parasporal crystalline inclusions within the mother cell. In most instances, the temporal and spatial regulation of ICP gene expression is determined at the transcriptional level by mother-cell-specific sigma factors that share homology with sigma E and sigma K from Bacillus subtilis. The cryIII ICP genes are a notable exception; these genes are transcribed from sigma A-like promoters during vegetative growth, are induced or derepressed at the onset of stationary phase, and are overexpressed in sporulation mutants of B. thuringiensis blocked in the phosphorylation of Spo0A, a key regulator of sporulation initiation. Transcription alone, however, cannot account for the impressive ability of this bacterium to accumulate insecticidal proteins. A variety of post-transcriptional and post-translational mechanisms also contribute to the efficient production of ICPs in B. thuringiensis, thus making this bacterium a cost-effective biological control agent.

Amino Acid Sequence↗
PubMed1998

Prevalence of beta-exotoxin, diarrhoeal toxin and specific delta-endotoxin in natural isolates of Bacillus thuringiensis.

Of newly isolated colonies with the appearance of Bacillus thuringiensis, 47.5% were found to produce the parasporal crystals characteristic of this species. These positive isolates were screened using the polymerase chain reaction for their possession of a gene encoding a specific protoxin type, CryIB. Strains with and without this gene were screened for their ability to produce beta-exotoxin and Bacillus cereus-type enterotoxin. It was found that 35% of the isolates possessed the cryIB gene; of these 83% also produced enterotoxin and 58% produced beta-exotoxin. No statistical significance was found for linkage between any of these characteristics. The probability, therefore, of isolating a strain of B. thuringiensis which specifically possessed the cryIB gene but did not produce either of the other, undesired, toxins, from the soil sample used, was 1.2%.

Adenosine↗
PubMed1993

Insertion sequence elements in Bacillus thuringiensis subsp. darmstadiensis.

Two variants of insertion sequence IS231, named IS231G and H, were isolated from Bacillus thuringiensis subsp. darmstadiensis 73-E-10-2 (BTD2), an isolate toxic to dipteran insects, and characterized by DNA sequence analysis. They are encoded consecutively as direct repeats on an EcoRI fragment of 5.6 kilo base pairs. Direct tandem repeats of IS231 elements have not been previously reported. Both elements are closely related to other members of the IS231 family that have been isolated from B. thuringiensis strains toxic to lepidopteran as well as to dipteran insects. A close correlation exists between the evolutionary relationships of the IS231 sequences determined to data and the toxicity spectrum of the host cell. Probing of BTD2 DNA with a radiolabeled IS231G fragment demonstrated that IS231 elements are located on 55- and 34-MDa plasmids as well as on chromosomal DNA. Chromosomal DNA, but not plasmids, from BTD2 also hybridizes to another, unrelated insertion sequence, IS240, from B. thuringiensis subsp. israelensis, an isolate toxic to dipteran insects. BTD2, therefore, contains IS elements once thought to reside exclusively in either dipteran- or lepidopteran-specific subspecies of B. thuringiensis.

Bacillus thuringiensis↗
PubMed1990

Plasmid-associated sensitivity of Bacillus thuringiensis to UV light.

Spores and vegetative cells of Bacillus thuringiensis were more sensitive to UV light than were spores or cells of plasmid-cured B. thuringiensis strains or of the closely related Bacillus cereus. Introduction of B. thuringiensis plasmids into B. cereus by cell mating increased the UV sensitivity of the cells and spores. Protoxins encoded by one or more B. thuringiensis plasmids were not involved in spore sensitivity, since a B. thuringiensis strain conditional for protoxin accumulation was equally sensitive at the permissive and nonpermissive temperatures. In addition, introduction of either a cloned protoxin gene, the cloning vector, or another plasmid not containing a protoxin gene into a plasmid-cured strain of B. thuringiensis all increased the UV sensitivity of the spores. Although the variety of small, acid-soluble proteins was the same in the spores of all strains examined, the quantity of dipicolinic acid was about twice as high in the plasmid-containing strains, and this may account for the differences in UV sensitivity of the spores. The cells of some strains harboring only B. thuringiensis plasmids were much more sensitive than cells of any of the other strains, and the differences were much greater than observed with spores.

Bacillus cereus↗