Immunological relationships among proteins making up the Bacillus thuringiensis subsp. israelensis crystalline toxin

Coexpression of chitinase and the cry11Aa1 toxin genes in Bacillus thuringiensis serovar israelensis

At the spore stage, a cloned chitinase gene was coexpressed with the regulatory gene p19 and the toxin gene cry11Aa1 in the hosts Bacillus thuringiensis serovar israelensis strains 4Q2-72 and c4Q2-72. The chitinase gene was derived from a high-chitinase producer, Bacillus licheniformis TP-1. Two transcriptional fusion plasmids between the p19 or p19-cry11Aa1 genes and the promoterless chitinase gene were constructed. In transcription order, the p16-19CHI construct contained the p19 gene together with the chitinase gene only while the p16-1968CHI construct contained p19 together with the toxin gene cry11Aa1 and the chitinase gene. The inserted sequences were regulated by a spore-specific promoter located upstream of p19. The recombinant chitinase of all transformed B. thuringiensis serovar israelensis strains was initially synthesized at low level at about 9 h of growth when a portion of the cells started to sporulate. It increased thereafter and reached maximum levels of 5.5, 4.9, and 4.7 mU/ml at 48 h, for strain 4Q2-72 transformed with p16-19CHI and p16-1968CHI and strain c4Q2-72 transformed with p16-19CHI, respectively. This activity was approximately 2 times higher than the maximum activity (2.7 mU/ml) of the parental strain, B. licheniformis TP-1. Although crude chitinase alone from B. thuringiensis serovar israelensis c4Q2-72 (p16-19CHI) at 4.5 mU/ml caused 40% mortality in second instar Aedes aegypti larvae, transformants containing the chitinase alone or in combination with cry11Aa1 resulted in lower toxicity to A. aegypti larvae than the untransformed 4Q2-72 host. For example the LC(50) for the transformed 4Q2-72 harboring the chitinase gene only (p16-19CHI) was 5.6 x 10(4) +/- 0.7 x 10(4) cells, 40 times higher than that of the untransformed host at 1.4 x 10(3) +/- 0.19 x 10(3). The lower toxicity correlated with poor sporulation in the transformants (i.e., 35 times lower than that in the untransformed host). However, the transformed 4Q2-72 strain expressing both the chitinase and the cry11Aa1 toxin genes (p16-1968CHI) were only 4-fold less toxic (LC(50) = 5.6 x 10(3) +/- 1.99 x 10(3)) than the untransformed 4Q2-72 hosts even though their spore count was 300 times lower. Since coapplication of crude chitinase from the cloned gene in recombinant strain (c4Q2-72 harboring p16-19CHI) with cell suspensions of B. thuringiensis serovar israelensis 4Q2-72 and its transformants could enhance 3- to 50-fold larvicidal activity, improvement in sporulation ability of these genetically engineered strains and cocrystallization of chitinase with crystal toxins may increase their potential for future insect control.

Bacillus thuringiensis crystal delta-endotoxin: role of proteases in the conversion of protoxin to toxin

The conversion of delta-endoprotoxins of Bacillus thuringiensis to active toxins is mediated by trypsin, insect gut (exogenous) and bacterial (endogenous) proteases. The biochemical aspects of exogenous and endogenous proteases involved in the conversion of protoxin to toxin are reviewed. Perhaps, these proteases also play a role in influencing the host range of toxin and in the development of resistance to toxin.

Biochemical, immunological and toxicological characteristics of the crystal proteins of Bacillus thuringiensis subsp. medellin

Characterization of the insecticidal and hemolytic activity of solubilized crystal proteins of Bacillus thuringiensis (Bt) subsp. medellin (Btmed) was performed and compared to solubilized crystal proteins of isolates 1884 of B. thuringiensis subsp. israelensis (Bti) and isolate PG-14 of B. thuringiensis subsp. morrisoni (Btm). In general, at acid pH values solubilization of the Bt crystalline parasporal inclusions (CPI) was lower than at alkaline pH. The larvicidal activity demonstrated by the CPI of Btmed indicated that optimal solubilization of CPI takes place at a pH value of 11.3, in Bti at pH values from 5.03 to 11.3 and in Btm at pH values from 9.05 to 11.3 Hemolytic activity against sheep red blood cells was mainly found following extraction at pH 11.3 in all Bt strains tested. Polyacrylamide gel electrophoresis under denaturing conditions revealed that optimal solubilization of the CPI in all Bt strains takes place at the alkaline pH values from 9.05 to 11.3. An enriched preparation of Btmed crystals was obtained, solubilized and crystal proteins were separated on a size exclusion column (Sephacryl S-200). Three main protein peaks were observed on the chromatogram. The first peak had two main proteins that migrate between 90 to 100 kDa. These proteins are apparently not common to other Bt strains isolated to date. The second and third peaks obtained from the size exclusion column yielded polypeptides of 68 and 28-30 kDa, respectively. Each peak independently, showed toxicity against 1st instar Culex quinquefasciatus larvae. Interestingly, combinations of the fractions corresponding to the 68 and 30 kDa protein showed an increased toxicity. These results suggest that the 94 kDa protein is an important component of the Btmed toxins with the highest potency to kill mosquito larvae. When crystal proteins of Bti were probed with antisera raised independently against the three main protein fractions of Btmed, the only crystal protein that showed cross reaction was the 28 kDa protein. These data suggest that Btmed could be an alternative bacterium for mosquito control programs in case mosquito larval resistance emerges to Bti toxic proteins.

Bacillus thuringiensis growth and toxicity. Basic and applied considerations

Despite the known importance of the composition of culture media and culture conditions on Bacillus thuringiensis growth and toxicity, very few reviews are concerned with this subject. This article reviews some aspects of the microbiology of Bacillus thuringiensis, and how toxicity is affected by the composition of growth media and bioreactor operation.

Mosquitocidal toxins of bacilli and their genetic manipulation for effective biological control of mosquitoes

The identification, cloning, and characterization of protein toxins from various species of bacilli have demonstrated the existence of mosquitocidal toxins with different structures, mechanisms of action, and host ranges. A start has been made in understanding the polypeptide determinants of toxicity and insecticidal activity, and the purification of toxins from recombinant organisms may lead to the elucidation of their X-ray crystal structures and the cloning of brush border membrane receptors. The results of cloning mosquitocidal toxins in heterologous microorganisms show the potential of expanding the range of susceptible mosquito species by combining several toxins of different host specificity in one cell. Toxins have been expressed in new microorganisms with the potential for increasing potency by persisting at the larval feeding zone. The powerful tools of bacterial genetics are being applied to engineer genetically stable, persistent toxin expression and expand the insecticidal host ranges of Bacillus sphaericus and Bacillus thuringiensis strains. These techniques, together with modern formulation technology, should eventually lead to the construction of mosquitocidal microorganisms which are effective enough to have a real impact on mosquito-borne diseases.

In vitro and in vivo proteolysis of the Bacillus thuringiensis subsp. israelensis CryIVD protein by Culex quinquefasciatus larval midgut proteases

Proteases with trypsin-, chymotrypsin- and thermolysin-like specificity were detected in Culex quinquefasciatus larval midguts. Their activities were monitored by N-terminal amino acid sequence analysis of the Bacillus thuringiensis subsp. israelensis CryIVD toxin proteolytic fragments. These proteases are located in the larval midgut and in different fractions obtained during the preparation of brush border membrane vesicles. The activity of the midgut proteases increased with an increase in pH. Both the chymotrypsin- and thermolysin-like activities are involved in the processing of solubilized CryIVD toxin, whereas an additional trypsin-like protease is necessary for the CryIVD parasporal inclusion processing. The solubilized CryIVD toxin was first cleaved between Thr347 and Phe348 and between Phe348 and Tyr349, generating a 40-kDa N-terminal fragment and a 32.5-kDa C-terminal fragment. The C-terminal domain was resistant to further processing, with only a small amount of a 31-kDa product appearing due to the action of a thermolysin-like protease. However, the N-terminal domain was very unstable, and was further degraded to about 30 kDa. Unlike the solubilized CryIVD toxin, the processing of the CryIVD parasporal inclusion was very slow at neutral pH. Three protease-resistant products were detected at pHs higher than 9.5 with an overnight incubation at 37 degrees C. The 30- and 28.5-kDa C-terminal peptides are proteolytic products of trypsin- and chymotrypsin-like proteases, respectively; while the 28-kDa N-terminal peptide has 27 amino acids deleted from the N-terminal end by a thermolysin-like protease.

Lepidopteran-specific crystal toxins from Bacillus thuringiensis form cation- and anion-selective channels in planar lipid bilayers

Previous studies in our laboratory have shown that CryIC, a lepidopteran-specific toxin from Bacillus thuringiensis, triggers calcium and chloride channel activity in SF-9 cells (Spodoptera frugiperda, fall armyworm). Chloride currents were also observed in SF-9 membrane patches upon addition of CryIC toxin to the cytoplasmic side of the membrane. In the present study the ability of activated CryIC toxin to form channels was investigated in a receptor-free, artificial phospholipid membrane system. We demonstrate that this toxin can partition in planar lipid bilayers and form ion-selective channels with a large range of conductances. These channels display complex activity patterns, often possess subconducting states and are selective to either anions or cations. These properties appeared to be pH dependent. At pH 9.5, cation-selective channels of 100 to 200 pS were most frequently observed. Among the channels recorded at pH 6.0, a 25-35 pS anion-selective channel was often seen at pH 6.0, with permeation and kinetic properties similar to those of the channels previously observed in cultured lepidopteran cells under comparable pH environment and for the same CryIC toxin doses. We conclude that insertion of CryIC toxin in SF-9 cell native membranes and in artificial planar phospholipid bilayers may result from an identical lipid-protein interaction mechanism.

Evaluation of synergism among Bacillus thuringiensis toxins

A simple test for synergism among toxins is described and applied to previously reported data on independent and joint toxicities of insecticidal proteins from Bacillus thuringiensis. The analysis shows synergism between a 27-kDa (CytA) toxin and 130- or 65-kDa (CryIV) toxins from B. thuringiensis subsp. israelensis against Aedes aegypti larvae. No positive synergism between 130- and 65-kDa toxins or among three CryIA toxins tested against seven species of Lepidoptera occurred. Comparisons with the original interpretations of these data show one case in which synergism occurred but was reported previously as absent and two cases that were not synergistic but were reported previously as suggestive of synergism. These results show that lack of an appropriate test for synergism can produce misleading conclusions. The methods described here can be used to test for synergistic effects of any poisons.

Proteolytic processing of the mosquitocidal toxin from Bacillus sphaericus SSII-1

The 97-kDa protein Mtx21, derived from the 100-kDa mosquitocidal protein (Mtx) from Bacillus sphaericus SSII-1 by the deletion of the putative signal sequence, was expressed as a fusion protein with glutathione S-transferase in Escherichia coli, and the fusion protein was purified by affinity chromatography. The fusion protein bound to glutathione agarose was cleaved with thrombin to release the Mtx21 protein. The 97-kDa Mtx21 protein was found to be toxic to Culex quinquefasciatus larvae with a 50% lethal concentration of 15 ng/ml. Treating Mtx21 with crude mosquito larval gut extracts gave rise to two major peptides of 70 and 27 kDa. Treating the 97-kDa Mtx21 protein with trysin also gave rise to a similar proteolytic cleavage pattern. N-terminal sequencing showed that the 27-kDa peptide was derived from the N-terminal region of the 97-kDa protein and that the 70-kDa protein was from the C-terminal region of the 97-kDa protein. The 27-kDa peptide has all the previously identified regions of homology with the catalytic peptides of the ADP-ribosyltransferase toxins, such as pertussis toxin S1 peptide, while the 70-kDa peptide has three internal regions of homology.

The parasporal inclusion of Bacillus thuringiensis subsp. shandongiensis: characterization and screening for insecticidal activity

The parasporal body of Bacillus thuringiensis subsp. shandongiensis was characterized in terms of its structure, protein composition, and toxicological properties against several types of insects. The crystals of B. thuringiensis shandongiensis appear to consist of a major protein of 144 kDa present in an spherical inclusion, as determined by transmission electron microscopy, titration curve analysis, and SDS-PAGE of the solubilized crystals. A second protein of ca. 60 kDa is present in trace amounts and appears to be associated with a small bar-shaped inclusion. The 144-kDa protein has been characterized by isoelectric point determination, N-terminal amino acid sequence analysis, amino acid analysis, and immunological cross reactivity. Its N-terminal amino acid sequence differed from that of other B. thuringiensis crystal proteins. The 144-kDa protein was not immunologically related to the crystal proteins of two toxic serovars (B. thuringiensis israelensis and B. thuringiensis kurstaki HD-1) and one nontoxic serovar (B. thuringiensis indiana), as shown in immunoblots probed with antiserum raised against the 144-kDa B. thuringiensis shandongiensis protein, the B. thuringiensis israelensis crystal proteins, and the trypsin resistant fragment of B. thuringiensis kurstaki P1 proteins. In contrast to most B. thuringiensis serovars, B. thuringiensis shandongiensis crystals did not dissolve at pH 12. Solubilization was achieved in sodium bicarbonate at pH 8.3 and in the presence of 25 mM dithiothreitol.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effect of a 20-kilodalton protein from Bacillus thuringiensis subsp. israelensis on production of the CytA protein by Escherichia coli

CytA, a 27-kDa cytolytic crystal protein of Bacillus thuringiensis subsp. israelensis, is produced only at very low levels by recombinant Escherichia coli cells unless a 20-kDa B. thuringiensis subsp. israelensis protein is also present (K. M. McLean and H. R. Whiteley, J. Bacteriol. 169:1017-1023, 1987; L. F. Adams, J. E. Visick, and H. R. Whiteley, J. Bacteriol. 171:521-530, 1989). However, the data reported here demonstrate that the 20-kDa protein is not required for high-level CytA production in E. coli strains carrying mutations in rpoH, groEL, or dnaK, all of which affect the proteolytic ability of the cells. The 20-kDa protein also increases the amount of CryIVD (another B. thuringiensis subsp. israelensis crystal protein) and LacZX90 (a mutant of beta-galactosidase) made by E. coli. The latter phenomenon is attributable to an increase in the half-life of LacZX90, suggesting that the 20-kDa protein may stabilize this protein. The effect of the 20-kDa protein was also examined in vitro and in a T7 RNA polymerase expression system, and the possible significance of these results for the timing of proteolysis and of 20-kDa protein activity is discussed. Finally, the ability of a single antibody to coimmunoprecipitate CytA and the 20-kDa protein from E. coli extracts provides evidence for a protein-protein interaction that may be related to the mechanism of action of the 20-kDa protein.

The Phylloplane as a Source of Bacillus thuringiensis Variants

Novel variants of Bacillus thuringiensis were isolated from the phylloplane of deciduous and conifer trees as well as of other plants. These isolates displayed a range of toxicity towards Trichoplusia ni. Immunoblot and toxin protein analysis indicate that these strains included representatives of the three principal B. thuringiensis pathotypes active against larvae of the orders Lepidoptera, Diptera, and Coleoptera. We propose that B. thuringiensis be considered part of the common leaf microflora of many plants.

A simple haemolytic method for quantitation of the delta endotoxin of Bacillus thuringiensis subsp. israelensis from crude samples

A simple haemolytic assay method for quantitative estimation of the delta endotoxin of Bacillus thuringiensis subsp. israelensis from a crude preparation has been developed. The method has several advantages over mosquito-larvicidal methods of assay as it is inexpensive, highly sensitive and easier to run and can be used for performing a reasonably large number of assays rapidly with high precision and with a coefficient of variation that does not exceed 1.96%.

Toxicity of protease-resistant domains from the delta-endotoxin of Bacillus thuringiensis subsp. israelensis in Culex quinquefasciatus and Aedes aegypti bioassays

The mosquitocidal glycoprotein endotoxin of Bacillus thuringiensis subsp. israelensis was digested with chymotrypsin to yield protease-resistant domains which were then separated from smaller protease digestion products by high-performance liquid chromatography. Once purified, the domains no longer bound wheat germ agglutinin, a lectin which binds N-acetylglucosamine (GlcNAc) and GlcNAc oligomers. Purified protease-resistant domains were as toxic for Culex quinquefasciatus larvae as intact solubilized toxin. In separate experiments, the toxicity of chymotrypsin-digested endotoxin for Aedes aegypti larvae was reduced fivefold or more. A model is presented in which GlcNAc-containing oligosaccharides are required for toxicity for A. aegypti larvae but not C. quinquefasciatus larvae.

Biosynthesis of 130-kilodalton mosquito larvicide in the cyanobacterium Agmenellum quadruplicatum PR-6

The 130-kilodalton mosquito larvicidal gene, cloned from Bacillus thuringiensis var. israelensis, was introduced into the cyanobacterium Agmenellum quadruplicatum PR-6 by plasmid transformation. Transformed cells synthesized 130-kilodalton delta-endotoxin protein and showed mosquito larvicidal activity. Results demonstrate a potential use of a cyanobacterium for biological control of mosquitoes.

Insecticidal crystal proteins of Bacillus thuringiensis

A classification for crystal protein genes of Bacillus thuringiensis is presented. Criteria used are the insecticidal spectra and the amino acid sequences of the encoded proteins. Fourteen genes are distinguished, encoding proteins active against either Lepidoptera (cryI), Lepidoptera and Diptera (cryII), Coleoptera (cryIII), or Diptera (cryIV). One gene, cytA, encodes a general cytolytic protein and shows no structural similarities with the other genes. Toxicity studies with single purified proteins demonstrated that every described crystal protein is characterized by a highly specific, and sometimes very restricted, insect host spectrum. Comparison of the deduced amino acid sequences reveals sequence elements which are conserved for Cry proteins. The expression of crystal protein genes is affected by a number of factors. Recently, two distinct sigma subunits regulating transcription during different stages of sporulation have been identified, as well as a protein regulating the expression of a crystal protein at a posttranslational level. Studies on the biochemical mechanisms of toxicity suggest that B. thuringiensis crystal proteins induce the formation of pores in membranes of susceptible cells. In vitro binding studies with radiolabeled toxins demonstrated a strong correlation between the specificity of B. thuringiensis toxins and the interaction with specific binding sites on the insect midgut epithelium. The expression of B. thuringiensis crystal proteins in plant-associated microorganisms and in transgenic plants has been reported. These approaches are potentially powerful strategies for the protection of agriculturally important crops against insect damage.

Specificity of action on mosquito larvae of Bacillus thuringiensis israelensis toxins encoded by two different genes

A 135 kDa protein gene and two open reading frames (ORF1 and ORF2) have been cloned from a large plasmid of Bacillus thuringiensis israelensis (Bourgouin et al. 1986). The Escherichia coli recombinant clones containing these genes were highly toxic to larvae of Aedes aegypti, Anopheles stephensi and Culex pipiens. From subcloning experiments it was deduced that the 135 kDa polypeptide alone was responsible for the toxic activity on both A. aegypti and An. stephensi larvae. In contrast, the presence of two polypeptides, the 135 kDa protein and the ORF1 product was required for toxicity to C. pipiens larvae. The minimal toxic fragment of the 135 kDa polypeptide has been delineated. The results indicate that a polypeptide of about 65 kDa, corresponding to an amino-terminal part of the 135 kDa protein is sufficient for toxicity. Sequence comparisons indicate that the ORF1 product may correspond to an N-terminal part of a rearranged 130 kDa protein.

A Bacillus thuringiensis subsp. israelensis gene encoding a 125-kilodalton larvicidal polypeptide is associated with inverted repeat sequences

A gene encoding a 125-kilodalton (kDa) mosquitocidal delta-endotoxin was cloned from the 72-MDa resident plasmid of Bacillus thuringiensis subsp. israelensis. This gene is similar in its 3' region to the gene encoding the 135-kDa protein previously cloned (C. Bourgouin, A. Klier, and G. Rapoport, Mol. Gen. Genet. 205:390-397, 1986). Escherichia coli recombinant clones harboring the 125-kDa gene were toxic to larvae of the three mosquito species Aedes aegypti, Anopheles stephensi, and Culex pipiens. In addition, the B. thuringiensis subsp. israelensis DNA fragment carrying the 125-kDa protein gene contains two sets of inverted repeat sequences, identified either by the S1 nuclease method or by electron microscopic observation. The structural organization of inverted repeat sequences and of the 125-kDa gene was analyzed and suggests that this B. thuringiensis subsp. israelensis delta-endotoxin gene is located within a transposable element.

Common features of Bacillus thuringiensis toxins specific for Diptera and Lepidoptera

The complete nucleotide sequence of a cloned gene encoding a 130-kDa crystal protein of Bacillus thuringiensis (B.t.) subspecies israelensis has been determined. The recombinant protein (Bt8) was purified and shown to be a mosquito-specific toxin with a LC50 value of 43 ng/ml to third-instar larvae of Aedes aegypti. Bt8 is processed by proteases or midgut extracts of mosquito larvae into toxic fragments of 68-78 kDa. Deletion mapping indicated that the active fragment of Bt8 is localized in the N-terminal half of the protoxin molecule. The deduced amino acid sequence of Bt8 has been compared with that of Bt2, a Lepidoptera-specific toxin, previously cloned from Bacillus thuringiensis berliner. Highly homologous amino acid stretches are present in the C-terminal half of the proteins. The N-terminal parts show much less sequence homology but they display a strikingly similar distribution of hydrophilic and hydrophobic amino acids. In addition, Bt8 and Bt2 show a significant immunological cross-reaction. The data indicate that although these B.t. delta endotoxins exhibit a different insect-host specificity, they are structurally related and might use a similar mechanism to interact with insect cell membranes.

Affinity purification of a 65-kilodalton parasporal protein from Bacillus thuringiensis PG-14 that shows mosquitocidal activity

By using antibody-mediated affinity chromatography, a highly mosquito larvicidal but nonhemolytic fraction was obtained from alkali-solubilized, silkworm (Bombyx mori) larval gut juice-treated parasporal inclusions of Bacillus thuringiensis strain PG-14 (serotype 8a:8b). This fraction contained a 65-kDa protein only but not a 25-kDa protein, the main component in the flow through fraction unbound to the affinity column. The 25-kDa protein purified from the unbound fraction by CM-cellulose chromatography demonstrated a high hemolytic activity against sheep red blood cells but very low mosquito larvicidal activity.

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.

The glycoprotein toxin of Bacillus thuringiensis subsp. israelensis indicates a lectinlike receptor in the larval mosquito gut

The mosquito-active protein crystals produced by Bacillus thuringiensis subsp. israelensis contain covalently attached aminosugars which are critical for their larvicidal activity. The 50% lethal concentrations toward Aedes aegypti larvae were increased up to 10-fold by mild periodate treatment, up to 40-fold by forming the protein crystals in the presence of tunicamycin, and up to 7-fold by the presence during the mosquito bioassays of N-acetylglucosamine or its trimer, triacetylchitotriose. Periodate-treated crystals and crystals formed in the presence of tunicamycin had greatly reduced binding capacities for wheat germ agglutinin, an N-acetylglucosamine-specific lectin. These results suggest that the B. thuringiensis subsp. israelensis glycoprotein toxin binds to a lectinlike receptor in the larval mosquito gut. Furthermore, the distinct lectin-binding patterns exhibited by diptera-active versus lepidoptera-active B. thuringiensis crystals suggest that host specificity for the microbial insecticides is determined, in part, by the carbohydrate portion of their glycoprotein crystals.

Similarities between crystal protein subunits of Bacillus thuringiensis strain 1884 serotype H14 and strain PG14 serotype H8a,8b, and their relationship with mosquitocidal activity

Bacillus thuringiensis subsp. israelensis strain 1884 and B. thuringiensis subsp. morrisoni strain PG14 have the same toxicity toward mosquito larvae. Their protein crystal contents were compared either on native electrophoretic systems or on gel filtration. Analysis of electroeluted native proteins in SDS-PAGE showed that the 28-Kd protein alone, without the 68- or 130-Kd protein, was not larvicidal; however, toxicity was recorded as soon as 28- and 68-Kd proteins were associated. After gel filtration of 1884 soluble crystal, the 68-Kd protein alone, without 28 or 130 Kd, was not toxic; toxicity was also recorded when 28- and 68-Kd proteins and higher molecular weight proteins were associated. A comparable pattern was observed with PG14 soluble crystals.

Structural disulfide bonds in the Bacillus thuringiensis subsp. israelensis protein crystal

We examined disulfide bonds in mosquito larvicidal crystals produced by Bacillus thuringiensis subsp. israelensis. Intact crystals contained 2.01 X 10(-8) mol of free sulfhydryls and 3.24 X 10(-8) mol of disulfides per mg of protein. Reduced samples of alkali-solubilized crystals resolved into several proteins, the most prominent having apparent molecular sizes of 28, 70, 135, and 140 kilodaltons (kDa). Nonreduced samples contained two new proteins of 52 and 26 kDa. When reduced, both the 52- and 26-kDa proteins were converted to 28-kDa proteins. Furthermore, both bands reacted with antiserum prepared against reduced 28-kDa protein. Approximately 50% of the crystal proteins could be solubilized without disulfide cleavage. These proteins were 70 kDa or smaller. Solubilization of the 135- and 140-kDa proteins required disulfide cleavage. Incubation of crystals at pH 12.0 for 2 h cleaved 40% of the disulfide bonds and solubilized 83% of the crystal protein. Alkali-stable disulfides were present in both the soluble and insoluble portions. The insoluble pellet contained 12 to 14 disulfides per 100 kDa of protein and was devoid of sulfhydryl groups. Alkali-solubilized proteins contained both intrachain and interchain disulfide bonds. Despite their structural significance, it is unlikely that disulfide bonds are involved in the formation or release of the larvicidal toxin.

Preliminary X-ray diffraction analysis of crystals of Bacillus thuringiensis toxin, a cell membrane disrupting protein

Crystals suitable for high resolution X-ray diffraction analysis have been reproducibly grown of the 24,000 Mr protein insect toxin from Bacillus thuringiensis. This protein, which demonstrates substantial insecticidal activity by inserting into phospholipid membranes, crystallizes as long square needles from polyethylene glycol 4000 at neutral pH. The crystals are of space group P4(1) and have cell dimensions of a = b = 33 A and c = 235 A, which suggests to us a predominantly helical motif for the protein's structure.

Purification of the mosquitocidal and cytolytic proteins of Bacillus thuringiensis subsp. israelensis

Two proteins from parasporal crystals of Bacillus thuringiensis subsp. israelensis were purified to electrophoretic homogeneity by gel filtration and anion-exchange chromatography. The larger of the two proteins (molecular weight, 68,000) was not cytolytic, whereas the smaller protein (molecular weight, 28,000) was highly cytolytic when assayed against rat erythrocytes. When these proteins were assayed against larvae of the yellow fever mosquito, Aedes aegypti, the larger protein was at least 100-fold more toxic than the smaller protein. Although proteolytic activity was not detected in solubilized crystals nor in purified protein preparations, the toxin (molecular weight, 68,000) was readily degraded to smaller, nontoxic molecules, even when maintained at 4 degrees C. Mixtures of the two purified proteins were significantly more toxic to mosquito larvae than was either protein alone. Thus, it is likely that both the mosquitocidal and the cytolytic protein play roles in the overall insecticidal action of the parasporal crystal produced by this bacterium.

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)