Molecular characterization of a gene encoding a 72-kilodalton mosquito-toxic crystal protein from Bacillus thuringiensis subsp. israelensis.

A gene encoding a 72,357-dalton (Da) crystal protein of Bacillus thuringiensis var. israelensis was isolated from a native 75-MDa plasmid by the use of a gene-specific oligonucleotide probe. Bacillus megaterium cells harboring the cloned gene (cryD) produced significant amounts of the 72-kDa protein (CryD), and the cells were highly toxic to mosquito larvae. In contrast, cryD-containing Escherichia coli cells did not produce detectable levels of the 72-kDa CryD protein. The sequence of the CryD protein, as deduced from the sequence of the cryD gene, was found to contain regions of homology with two previously described B. thuringiensis crystal proteins: a 73-kDa coleopteran-toxic protein and a 66-kDa lepidopteran- and dipteran-toxic protein of B. thuringiensis subsp. kurstaki. A second gene encoding the B. thuringiensis subsp. israelensis 28-kDa crystal protein was located approximately 1.5 kilobases upstream from and in the opposite orientation to the cryD gene.     

Deletion by in vivo recombination shows that the 28-kilodalton cytolytic polypeptide from Bacillus thuringiensis subsp. israelensis is not essential for mosquitocidal activity.

The cytA gene encoding the 28-kDa polypeptide of Bacillus thuringiensis subsp. israelensis crystals was disrupted in the 72-MDa resident plasmid by in vivo recombination, thus indicating that homologous recombination occurs in B. thuringiensis. The absence of the 28-kDa protein in B. thuringiensis did not affect the crystallization of the other toxic components of the parasporal body (68-, 125-, and 135-kDa polypeptides). The absence of the 28-kDa protein abolished the hemolytic activity of B. thuringiensis subsp. israelensis crystals. However, the mosquitocidal activity of the 28-kDa protein-free crystals did not differ significantly from that of the wild-type crystals when tested on Aedes aegypti and Culex pipiens larvae. The 28-kDa protein contributed slightly to the toxicity to Anopheles stephensi larvae. This indicates that the 28-kDa protein is not essential for mosquitocidal activity, at least against the three species tested.     

Identification of a delta-Endotoxin Gene Product Specifically Active against Spodoptera littoralis Bdv. among Proteolysed Fractions of the Insecticidal Crystals of Bacillus thuringiensis subsp. aizawai 7.29

At least three different insecticidal crystal protein genes were shown to be expressed in Bacillus thuringiensis subsp. aizawai 7.29, a strain that is potentially active against the cotton leafworm Spodoptera littoralis Bdv. Among crude K-60 fractions (60- to 70-kilodalton [kDa] molecules) that were products of proteolysed crystals containing the active domains of the protoxin molecules, we were able to distinguish several distinct components on the basis of their antigenic relationship and their larvicidal properties. A purified fraction designated SF2 was a 61-kDa component specifically active against Pieris brassicae L. and homologous to the B. thuringiensis subsp. berliner 1715 plasmid-encoded crystal protein. A second fraction designated SF1 was composed of 63- and 65-kDa polypeptides and was specifically active against S. littoralis. The SF1 fraction and particularly the 65-kDa component were not antigenically related to the 61-kDa component. The purified fractions were compared with the products of three different crystal protein genes we previously cloned from total DNA of B. thuringiensis subsp. aizawai, among them a new type of crystal protein gene encoding a protein that is specifically active against S. littoralis and other insects of the Noctuidae family. This approach led us to consider the 65-kDa component as a minimum active part of a delta-endotoxin that is encoded by this new gene. Products of the two other cloned genes can be correlated with the 61- and 63-kDa components, respectively. Thus, in B. thuringiensis subsp. aizawai 7.29, multiple delta-endotoxin genes of different structural types direct the synthesis of several delta-endotoxins with different host specificities which were identified as components of the insecticidal crystals.     

Nucleotide sequence and deduced amino acid sequence of a coleopteran-active delta-endotoxin gene from Bacillus thuringiensis subsp. san diego

A gene from Bacillus thuringiensis subsp. san diego that is responsible for a delta-endotoxin active against Colorado potato beetle and some other Coleoptera was sequenced and shown to have surprising regional homology with both lepidopteran and dipteran active delta-endotoxins from other strains of B. thuringiensis. Unlike the lepidopteran active toxins from B. thuringiensis subsp. kurstaki that exist as approx. 130-kDa protoxins and form bipyramidal crystalline inclusions, the coleopteran toxic protein forms a square-shaped crystal composed of an approx. 65-kDa protein. Comparisons of the gene sequences encoding the active portions of these protoxins indicate conservation of N-terminal hydrophilic and hydrophobic regions, and suggest a distant ancestral origin for these insecticidal proteins.     

Structural relatedness between mosquitocidal endotoxins of Bacillus thuringiensis subsp. israelensis.

A mosquitocidal toxin gene, cloned from Bacillus thuringiensis subsp. israelensis, was introduced into mutant crystal-negative B. thuringiensis subsp. israelensis cells. Partial toxicity to mosquitos was restored. The 58-kilodalton cloned gene product is a minor protein component of B. thuringiensis subsp. israelensis crystals and is structurally related to a major, 135-kilodalton crystal toxin.     

Structural relatedness between mosquitocidal endotoxins of Bacillus thuringiensis subsp. israelensis

A mosquitocidal toxin gene, cloned from Bacillus thuringiensis subsp. israelensis, was introduced into mutant crystal-negative B. thuringiensis subsp. israelensis cells. Partial toxicity to mosquitos was restored. The 58-kilodalton cloned gene product is a minor protein component of B. thuringiensis subsp. israelensis crystals and is structurally related to a major, 135-kilodalton crystal toxin.     

Minireplicon from pBtoxis of Bacillus thuringiensis subsp. israelensis

A 2.2-kb fragment containing a replicon from pBtoxis, the large plasmid that encodes the insecticidal endotoxins of Bacillus thuringiensis subsp. israelensis, was identified, cloned, and sequenced. This fragment contains cis elements, including iterons, found in replication origins of other large plasmids and suggests that pBtoxis replicates by a type A theta mechanism. Two genes, pBt156 and pBt157, encoding proteins of 54.4 kDa and 11.8 kDa, respectively, were present in an operon within this minireplicon, and each was shown by deletion analysis to be essential for replication. The deduced amino acid sequences of the 54.4-kDa and 11.8-kDa proteins showed no substantial homology with known replication (Rep) proteins. However, the 54.4-kDa protein contained a conserved FtsZ domain, and the 11.8 kDa protein contained a helix-turn-helix motif. As FtsZ proteins have known functions in bacterial cell division and the helix-turn-helix motif is present in Rep proteins, it is likely that these proteins function in plasmid replication and partitioning. The minireplicon had a copy number of two or three per chromosome equivalent in B. thuringiensis subsp. israelensis but did not replicate in B. cereus, B. megaterium, or B. subtilis. A plasmid constructed to synthesize large quantities of the Cry11A and Cyt1A endotoxins demonstrated that this minireplicon can be used to engineer vectors for cry and cyt gene expression.     

Properties of a 72-kilodalton mosquitocidal protein from Bacillus thuringiensis subsp. morrisoni PG-14 expressed in B. thuringiensis subsp. kurstaki by using the shuttle vector pHT3101.

The mosquitocidal properties of Bacillus thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni PG-14 are attributable to protein inclusions grouped together within a parasporal body. In both of these strains, the mosquitocidal activity resides in proteins with molecular masses of 27, 72, 128, and 135 kDa. In an attempt to determine the toxicity of each protein, the shuttle vector pHT3101 was used to express the cryIVD gene (encoding the 72-kDa CryIVD protein) from B. thuringiensis subsp. morrisoni in an acrystalliferous mutant of B. thuringiensis subsp. kurstaki. With this system, parasporal inclusions of the 72-kDa protein were obtained that were comparable in size, shape, and toxicity to those produced by parental B. thuringiensis subsp. morrisoni. The inclusions were bar shaped, measured 500 by 300 by 150 nm, and were easily visible with phase-contrast microscopy by 16 h of cell growth. A 50% lethal concentration of 64 ng/ml for these inclusions was determined in bioassays against fourth instars of Culex quinquefasciatus, which was similar to the 50% lethal concentration of 55 ng/ml obtained for the 72-kDa inclusion from B. thuringiensis subsp. israelensis. In contrast, expression of the cryIVD gene in Escherichia coli was very low and only detectable by immunoblot analysis. These results demonstrate that the pHT3101-B. thuringiensis expression system can be used to express the CryIVD protein in quantities and with properties comparable to that obtained with the natural host. This system may prove useful for the expression of other B. thuringiensis proteins and, in particular, for reconstitution experiments with inclusions produced by the mosquitocidal subspecies of B. thuringiensis.     

Properties of a 72-kilodalton mosquitocidal protein from Bacillus thuringiensis subsp. morrisoni PG-14 expressed in B. thuringiensis subsp. kurstaki by using the shuttle vector pHT3101.

The mosquitocidal properties of Bacillus thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni PG-14 are attributable to protein inclusions grouped together within a parasporal body. In both of these strains, the mosquitocidal activity resides in proteins with molecular masses of 27, 72, 128, and 135 kDa. In an attempt to determine the toxicity of each protein, the shuttle vector pHT3101 was used to express the cryIVD gene (encoding the 72-kDa CryIVD protein) from B. thuringiensis subsp. morrisoni in an acrystalliferous mutant of B. thuringiensis subsp. kurstaki. With this system, parasporal inclusions of the 72-kDa protein were obtained that were comparable in size, shape, and toxicity to those produced by parental B. thuringiensis subsp. morrisoni. The inclusions were bar shaped, measured 500 by 300 by 150 nm, and were easily visible with phase-contrast microscopy by 16 h of cell growth. A 50% lethal concentration of 64 ng/ml for these inclusions was determined in bioassays against fourth instars of Culex quinquefasciatus, which was similar to the 50% lethal concentration of 55 ng/ml obtained for the 72-kDa inclusion from B. thuringiensis subsp. israelensis. In contrast, expression of the cryIVD gene in Escherichia coli was very low and only detectable by immunoblot analysis. These results demonstrate that the pHT3101-B. thuringiensis expression system can be used to express the CryIVD protein in quantities and with properties comparable to that obtained with the natural host. This system may prove useful for the expression of other B. thuringiensis proteins and, in particular, for reconstitution experiments with inclusions produced by the mosquitocidal subspecies of B. thuringiensis.     

Mosquitocidal activity of the CryIC delta-endotoxin from Bacillus thuringiensis subsp. aizawai.

The cloned 135-kDa CryIC delta-endotoxin from Bacillus thuringiensis is a lepidopteran-active toxin, displaying high activity in vivo against Spodoptera litoralis and Spodoptera frugiperda larvae and in vitro against the S. frugiperda Sf9 cell line. Here, we report that the CryIC delta-endotoxin cloned from B. thuringienesis subsp. aizawai HD-229 and expressed in an acrystalliferous B. thuringiensis strain is also toxic to Aedes aegypti, Anophles gambiae, and Culex quinquefasciatus mosquito larvae. Furthermore, when solubilized and proteolytically activated by insect gut extracts, CryIC is cytotoxic to cell lines derived from the first two of these dipteran insects. This activity was not observed for two other lepidopteran-active delta-endotoxins, CryIA(a) and CryIA(c). However, in contrast to the case with a lepidopteran and dipteran delta-endotoxin cloned from B. thuringiensis subsp. aizawai IC1 (M.Z. Haider, B. H. Knowles, and D. J. Ellar, Eur. J. Biochem. 156:531-540, 1986), no differences in the in vitro specificity or processing of CryIC were found when it was activated by lepidopteran or dipteran gut extract. The recombinant CryIC delta-endotoxin expressed in Escherichia coli was also toxic to A. aegypti larvae. By contrast, a second cryIC gene cloned from B. thuringiensis subsp. aizawai 7.29 (V. Sanchis, D. Lereclus, G. Menou, J. Chaufaux, S. Guo, and M. M. Lecadet, Mol. Microbiol. 3:229-238, 1989) was nontoxic. DNA sequencing showed that the two genes were identical. However, CryIC from B. thuringiensis subsp. aizawai 7.29 had been cloned with a truncated C terminus, and when it was compared with the full-length CryIC delta-endotoxin, it was found to be insoluble under alkaline reducing conditions. These results show that CryIC from B. thuringiensis subsp. aizawai is a dually active delta-endotoxin.     

Cytolytic activity and immunological similarity of the Bacillus thuringiensis subsp. israelensis and Bacillus thuringiensis subsp. morrisoni isolate PG-14 toxins.

The parasporal bodies of the mosquitocidal isolates of Bacillus thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 were compared with regard to their hemolytic and cytolytic activities and the immunological relatedness of the 28- and 65-kilodalton (kDa) proteins that occur in both subspecies. The alkali-solubilized parasporal bodies of B. thuringiensis subsp. israelensis caused 50% lysis of human erythrocytes at 1.14 micrograms/ml, whereas those of B. thuringiensis subsp. morrisoni caused similar lysis at 1.84 micrograms/ml. Preincubation of solubilized parasporal bodies with dioleolyl phosphatidylcholine significantly inhibited the hemolytic activity of both supspecies. In cytolytic assays against Aedes albopictus cells, the toxin concentrations causing 50% lysis for B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni were 1.87 and 11.98 micrograms/ml, respectively. Polyclonal antibodies raised separately against the 25-kDa protein (a tryptic digest of the 28-kDa protein) or the 65-kDa protein of B. thuringiensis subsp. israelensis cross-reacted, respectively, with the 28- and the 65-kDa proteins of B. thuringiensis subsp. morrisoni. However, neither of these antibodies cross-reacted with the 135-kDa protein of either subspecies. These results indicate that the mosquitocidal and hemolytic properties of B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 are probably due to the biologically related proteins that are present in the parasporal bodies of both subspecies. The lower hemolytic activity of the B. thuringiensis subsp. morrisoni may be due to the presence of lower levels of the 28-kDa protein in that subspecies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytolytic activity and immunological similarity of the Bacillus thuringiensis subsp. israelensis and Bacillus thuringiensis subsp. morrisoni isolate PG-14 toxins

The parasporal bodies of the mosquitocidal isolates of Bacillus thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 were compared with regard to their hemolytic and cytolytic activities and the immunological relatedness of the 28- and 65-kilodalton (kDa) proteins that occur in both subspecies. The alkali-solubilized parasporal bodies of B. thuringiensis subsp. israelensis caused 50% lysis of human erythrocytes at 1.14 micrograms/ml, whereas those of B. thuringiensis subsp. morrisoni caused similar lysis at 1.84 micrograms/ml. Preincubation of solubilized parasporal bodies with dioleolyl phosphatidylcholine significantly inhibited the hemolytic activity of both supspecies. In cytolytic assays against Aedes albopictus cells, the toxin concentrations causing 50% lysis for B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni were 1.87 and 11.98 micrograms/ml, respectively. Polyclonal antibodies raised separately against the 25-kDa protein (a tryptic digest of the 28-kDa protein) or the 65-kDa protein of B. thuringiensis subsp. israelensis cross-reacted, respectively, with the 28- and the 65-kDa proteins of B. thuringiensis subsp. morrisoni. However, neither of these antibodies cross-reacted with the 135-kDa protein of either subspecies. These results indicate that the mosquitocidal and hemolytic properties of B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 are probably due to the biologically related proteins that are present in the parasporal bodies of both subspecies. The lower hemolytic activity of the B. thuringiensis subsp. morrisoni may be due to the presence of lower levels of the 28-kDa protein in that subspecies.(ABSTRACT TRUNCATED AT 250 WORDS)     

A 20-kilodalton protein is required for efficient production of the Bacillus thuringiensis subsp. israelensis 27-kilodalton crystal protein in Escherichia coli.

The 27-kilodalton (kDa) mosquitocidal protein gene from Bacillus thuringiensis subsp. israelensis has been cloned as a 10-kilobase (kb) HindIII fragment from plasmid DNA; efficient expression in Escherichia coli KM1 depends on a region of DNA located approximately 4 kb upstream (K. McLean and H. R. Whiteley, J. Bacteriol. 169:1017-1023, 1987). We have cloned the upstream DNA region and show that it contains a complete open reading frame (ORF) encoding a protein with a molecular mass of 19,584 Da. Sequencing of adjacent stretches of DNA revealed two partial ORFs: one has 55.2% identity in an overlap of 319 amino acids to the putative transposase of IS231 of B. thuringiensis subsp. thuringiensis, and the other, a 78-codon partial ORF, may be the carboxyl terminus of the 67-kDa protein previously observed in maxicells of strain KM1. A 0.8-kb fragment containing only the 20-kDa protein gene greatly enhanced the expression of the 27-kDa protein in E. coli. The introduction of nonsense codons into the 20-kDa protein gene ORF abolished this effect, indicating that the gene product, not the mRNA or DNA, is required for the enhancement. The effect of the 20-kDa protein gene on various fusions of lacZ to the 27-kDa protein gene suggests that the 20-kDa protein acts after the initiation of translation of the 27-kDa protein gene.     

Cloning and expression of Bacillus thuringiensis israelensis delta-endotoxin DNA in B. sphaericus

Bacillus thuringiensis israelensis delta-endotoxin genes were cloned into Bacillus sphaericus 2362, producing stable transformants reacting with antibody to the 28- and 65-kDa B. thuringiensis israelensis crystal proteins and approximately 10 times more toxic to Aedes mosquito larvae than the original host strain. The LC50 after 48 hr of exposure of Aedes larvae to the most active transformed clone was 0.19 microgram/ml, compared with an LC50 of 1.9 microgram/ml for B. sphaericus 2362 and less than 0.1 microgram/ml for B. thuringiensis israelensis. The cloning vector, plasmid pPL603E, was also effective in transforming B. subtilis 1E20 with B. thuringiensis israelensis DNA, producing highly toxic clones with less stable gene expression than the clones of B. sphaericus.     

Cloning and expression of a novel toxin gene from Bacillus thuringiensis subsp. jegathesan encoding a highly mosquitocidal protein.

A gene, designated cry11B, encoding a 81,293-Da crystal protein of Bacillus thuringiensis subsp. jegathesan was cloned by using a gene-specific oligonucleotide probe. The sequence of the Cry11B protein, as deduced from the sequence of the cry11B gene, contains large regions of similarity with the Cry11A toxin (previously CryIVD) from B. thuringiensis subsp. israelensis. The Cry11B protein was immunologically related to both Cry11A and Cry4A proteins. The cry11B gene was expressed in a nontoxic strain of B. thuringiensis, in which Cry11B was produced in large amounts during sporulation and accumulated as inclusions. Purified Cry11B inclusions were highly toxic for mosquito larvae of the species Aedes aegypti, Culex pipiens, and Anopheles stephensi. The activity of Cry11B toxin was higher than that of Cry11A and similar to that of the native crystals from B. thuringiensis subsp. jegathesan, which contain at least seven polypeptides.     

Micro-lipid-droplet encapsulation of Bacillus thuringiensis subsp. israelensis delta-endotoxin for control of mosquito larvae.

The crystal delta-endotoxin of Bacillus thuringiensis subsp. israelensis is less toxic to larvae of Anopheles freeborni than to larvae of Aedes aegypti. However, when solubilized crystal was used, larvae from both species showed similar sensitivities. This effect presumably was due to the differences in feeding behavior between the two mosquito larvae when crystal preparations are used. A procedure is described whereby both crystal and solubilized B. thuringiensis subsp. israelensis toxin were emulsified with Freund incomplete adjuvant, with retention of toxicity. The use of Freund incomplete adjuvant also allowed one to assay the solubilized toxin at a low nanogram level. Furthermore, coating the toxin with lipophilic material altered the buoyancy of the toxin and reversed the sensitivities of the two mosquito larvae toward the B. thuringiensis subsp. israelensis toxin. This difference in buoyancy was determined by using an enzyme-linked immunosorbent assay that was specific for the toxic peptides. These data indicate that economically feasible buoyant formulations for the B. thuringiensis subsp. israelensis crystal can be developed.     

Cloning of novel enterotoxin genes from Bacillus cereus and Bacillus thuringiensis.

A novel enterotoxin gene was cloned from Bacillus cereus FM1, and its nucleotide sequence was determined. Previously, a 45-kDa protein causing characteristic enterotoxin symptoms in higher animals had been isolated (K. Shinagawa, p. 181-193, in A. E. Pohland et al., ed., Microbial Toxins in Foods and Feeds, 1990) from the same B. cereus strain, but no report of cloning of the enterotoxin gene has been published. In the present study, a specific antibody to the purified enterotoxin was produced and used to screen the genomic library of B. cereus FM1 made with the lambda gt11 vector. An immunologically positive clone was found to contain the full protein-coding region and some 5' and 3' flanking regions. The deduced amino acid sequence of the cloned gene indicated that the protein is rich in beta structures and contains some unusual sequences, such as consecutive Asn residues. In order to clone enterotoxin genes from Bacillus thuringiensis, two PCR primers were synthesized based on the nucleotide sequence of the B. cereus gene. These primers were designed to amplify the full protein-coding region. PCR conducted with DNA preparations from the B. thuringiensis subsp. sotto and B. thuringiensis subsp. israelensis strains successfully amplified a segment of DNA with a size almost identical to that of the protein-coding region of the B. cereus enterotoxin. Nucleotide sequences of the amplified DNA segments showed that these B. thuringiensis strains contain an enterotoxin gene very similar to that of B. cereus. Further PCR screening of additional B. thuringiensis strains with four primer pairs in one reaction revealed that some additional B. thuringiensis strains contain enterotoxin-like genes.