Characterization of a Novel Strain of Bacillus thuringiensis

New native Bacillus thuringiensis strains induce high insecticidal action against Culex pipiens pallens larvae and adults

Mosquitoes of many species are key disease vectors, killing millions of people each year. Bacillus thuringiensis-based insecticide formulations are largely recognized as among the most effective, ecologically safe, and long-lasting methods of managing insect pests. New B. thuringiensis strains with high mosquito control effectiveness were isolated, identified, genetically defined, and physiologically characterized. Eight B. thuringiensis strains were identified and shown to carry endotoxin-producing genes. Using a scanning electron microscope, results revealed typical crystal forms of various shapes in B. thuringiensis strains. Fourteen cry and cyt genes were found in the strains examined. Although the genome of the B. thuringiensis A4 strain had twelve cry and cyt genes, not all of them were expressed, and only a few protein profiles were observed. The larvicidal activity of the eight B. thuringiensis strains was found to be positive (LC50: 1.4-28.5 g/ml and LC95: 15.3-130.3 g/ml). Bioassays in a laboratory environment demonstrated that preparations containing B. thuringiensis spores and crystals were particularly active to mosquito larvae and adults. These new findings show that the novel preparation containing B. thuringiensis A4 spores and crystals mixture might be used to control larval and adult mosquitoes in a sustainable and ecologically friendly manner.

Genetic Modification Approaches for Parasporins Bacillus thuringiensis Proteins with Anticancer Activity

Bacillus thuringiensis (Bt) is a bacterium capable of producing Cry toxins, which are recognized for their bio-controlling actions against insects. However, a few Bt strains encode proteins lacking insecticidal activity but showing cytotoxic activity against different cancer cell lines and low or no cytotoxicity toward normal human cells. A subset of Cry anticancer proteins, termed parasporins (PSs), has recently arisen as a potential alternative for cancer treatment. However, the molecular receptors that allow the binding of PSs to cells and their cytotoxic mechanisms of action have not been well established. Nonetheless, their selective cytotoxic activity against different types of cancer cell lines places PSs as a promising alternative treatment modality. In this review, we provide an overview of the classification, structures, mechanisms of action, and insights obtained from genetic modification approaches for PS proteins.

Molecular Diversity of Bacillus thuringiensis and Bioinformatics Analysis of Local Isolate of Auky Island, Padaido District in Biak Numfor Papua as a Control of Anopheles Mosquito Larvae

This research aims to analyze the level of similarity and diversity among local isolates of B. thuringiensis Auky Island Padaido District in Biak Numfor Regency with NCBI gene bank base, the basis of which is to obtain B. thuringiensis isolates from jayapura local isolates that can act as controllers of Anopheles mosquito larvae. Several steps in the research are 16s gene amplification, PCR product purification, cloning using pTA2 vectors and transformation into competent E. coli Zymo 5α cells, confirmation with PCR colonies, recombinant plasmid isolation, sequencing analysis and phylogenetic tree construction. The isolates of ABNP8, ABNP9, ABNP11, ABNP12 and ABNP18 have been detected as local isolates from in Auky Island Padaido District in Biak Numfor Papua Regency that have great potential as bioinsecticides, and capable of controlling and killing Anopheles mosquito larvae. Of the five isolates, ABNP8 isolates had unique diversity and characteristics and were different from the four other isolates. Based on the similarity analysis in the MEGA7 program, the similarity rate reached 84%. Its diversity can be seen from the uniqueness of the sequence and its position in different branching dendrograms.

Importance of Cry Proteins in Biotechnology: Initially a Bioinsecticide, Now a Vaccine Adjuvant

A hallmark of Bacillus thuringiensis bacteria is the formation of one or more parasporal crystal (Cry) proteins during sporulation. The toxicity of these proteins is highly specific to insect larvae, exerting lethal effects in different insect species but not in humans or other mammals. The aim of this review is to summarize previous findings on Bacillus thuringiensis, including the characteristics of the bacterium, its subsequent contribution to biotechnology as a bioinsecticide due to the presence of Cry proteins, and its potential application as an adjuvant. In several studies, Cry proteins have been administered together with specific antigens to immunize experimental animal models. The results have shown that these proteins can enhance immunogenicity by generating an adequate immune response capable of protecting the model against an experimental infectious challenge, whereas protection is decreased when the specific antigen is administered without the Cry protein. Therefore, based on previous results and the structural homology between Cry proteins, these molecules have arisen as potential adjuvants in the development of vaccines for both animals and humans. Finally, a model of the interaction of Cry proteins with different components of the immune response is proposed.

Search for Cry proteins expressed by Bacillus spp. genomes, using hidden Markov model profiles

This report focuses on a systematic search for Cry proteins in Bacillus spp. other than B. thuringiensis by analyzing reported Bacillus spp. genomes, using conserved sequences from the C-terminal half of reported Cry proteins in hidden Markov model profiles. A high-throughput model based on the use of HMMER and CD-HIT tools was designed, which identified Cry proteins. This model was used on 857 reported Bacillus spp. genomes, where 174 Cry protein sequences were identified, mostly, as expected, in B. thuringiensis genomes but, interestingly, 42 were identified on other species. Despite including 89 species of Bacillus in the HMMER analysis, Cry protein sequences were found only in genomes from species within the B. cereus group. According to the species registered at the NCBI database containing each genome, this group was formed by 18 non-B. thuringiensis strains. However, when sequences in those genomes were analyzed by multilocus sequence typing, the number of non-B. thuringiensis strains increased to 39, indicating that as many as 119 Cry protein sequences were found in four non-B. thuringiensis species. Therefore, dispersion of Cry proteins is much wider and frequent than previously thought, questioning its role in nature.

Diversity of Bacillus thuringiensis Strains From Qatar as Shown by Crystal Morphology, δ-Endotoxins and Cry Gene Content

Bacillus thuringiensis (Bt) based insecticidal formulations have been recognized as one of the most successful, environmentally safe and sustainable method of controlling insect pests. Research teams worldwide are in search of Bt diversity giving more choices of bio-insecticides and alternatives to address insect resistance. In fact, there are many unexplored ecologies that could harbor novel Bt strains. This study is the first initiative to explore Bt strain diversity in Qatar. A collection of 700 Bt isolates was constructed. Scanning electron microscopy of Bt crystals showed different crystal forms, with a high abundance of spherical crystals compared to the bipyramidal ones. Among the spherical crystals, four different morphologies were observed. The δ-endotoxin content of parasporal crystals from each Bt isolate revealed that there are 16 different protein profiles among the isolates of the collection. On the other hand, plasmid pattern analysis showed seven different plasmid profiles. Their insecticidal activity was predicted by exploring the δ-endotoxin coding genes and conducting qualitative insecticidal bioassays. 19 smooth spherical crystal producing isolates have been identified that could be possible candidates for endotoxin production targeting Dipteran insects. Another group of 259 isolates producing bipyramidal and cuboidal crystals could target Lepidopteran and Coleopteran insects. The remaining 422 isolates have novel profiles. In conclusion, Qatari soil ecology provides a good collection and diversity of Bt isolates. In addition to strains harboring genes encoding common endotoxins, the majority are different and very promising for the search of novel insecticidal endotoxins.

Assessment of the Antimicrobial Activity and the Entomocidal Potential of Bacillus thuringiensis Isolates from Algeria

This work represents the first initiative to analyze the distribution of B. thuringiensis in Algeria and to evaluate the biological potential of the isolates. A total of 157 isolates were recovered, with at least one isolate in 94.4% of the samples. The highest Bt index was found in samples from rhizospheric soil (0.48) and from the Mediterranean area (0.44). Most isolates showed antifungal activity (98.5%), in contrast to the few that had antibacterial activity (29.9%). A high genetic diversity was made evident by the finding of many different crystal shapes and various combinations of shapes within a single isolate (in 58.4% of the isolates). Also, over 50% of the isolates harbored cry1, cry2, or cry9 genes, and 69.3% contained a vip3 gene. A good correlation between the presence of chitinase genes and antifungal activity was observed. More than half of the isolates with a broad spectrum of antifungal activity harbored both endochitinase and exochitinase genes. Interestingly, 15 isolates contained the two chitinase genes and all of the above cry family genes, with some of them harboring a vip3 gene as well. The combination of this large number of genes coding for entomopathogenic proteins suggests a putative wide range of entomotoxic activity.

Curing of plasmid pBMB28 from Bacillus thuringiensis YBT-020 using an unstable replication region

Bacillus thuringiensis serovar finitimus strain YBT-020 is the well-studied spore-crystal association (SCA) phenotypic strain, whose parasporal crystals adhere to spore after lysis of the mother cell. Its endogenous plasmids pBMB26 and pBMB28 were proved essential for this SCA phenotype. In our previous study, using conventional methods, pBMB26 cured derivative and both pBMB26 and pBMB28 cured derivative of YBT-020 were obtained. However, YBT-020 solely cured of pBMB28 could not be obtained. In this study, an unstable replication region of pBMB28 was identified and was used to construct an incompatible plasmid pRep28B. This incompatible plasmid was successfully used to cure plasmid pBMB28 and was easily eliminated through segregational instability under the optimum growth temperature of YBT-020. Therefore, an endogenous plasmid was cured from the B. thuringiensis strain utilizing plasmid incompatibility. Moreover, using an unstable replication region instead of a temperature sensitive (Ts) replication region is better to cure the incompatible plasmid because it can avoid culturing at higher temperature. This method provides an efficient method for plasmid curing in B. thuringiensis and other bacteria.

Characterization of parasporin gene harboring Indian isolates of Bacillus thuringiensis

Bacillus thuringiensis (Bt) is popularly known as insecticidal bacterium. However, non-insecticidal Bt strains are more extensively available in natural environment than the insecticidal ones. Parasporin (PS) is a collection of genealogically heterogeneous Cry proteins synthesized in non-insecticidal isolates of Bt. An important character generally related with PS proteins is their strong cytocidal activity preferentially on human cancer cells of various origins. Identification and characterization of novel parasporin protein which are non-hemolytic and non-insecticidal but having selective anticancer activity raise the possibility of a novel application of Bt in medical field. In the present study, seven new indigenous isolates (T6, T37, T68, T98, T165, T186, and T461) of Bt showed variation in colony morphology, crystal characters and protein profiles with each other. Out of the seven new isolates screened for parasporin (ps) and cry genes, two of the new indigenous isolates (T98 and T186) of Bt showed the presence of ps4 gene. Partial ps4 gene was cloned from the two new isolates and the sequence of partial ps4 gene showed high homology with its holotype ps4Aa1. These two isolates were characterized based on the proteolytic processing of the inclusion proteins and the proteolytic products were found to be comparable to the PS4 reference strain A1470. The two isolates of Bt did not show toxicity toward Spodoptera litura and Helicoverpa armigera. Based on the results of this study, it can be concluded that the isolates T98 and T186 are parasporin producers.

Microscopic analysis of a native Bacillus thuringiensis strain from Malaysia that produces exosporium-enclosed parasporal inclusion

The current study focused on the microscopic studies of a native Bacillus thuringiensis strain isolated from Malaysia, Bt-S84-13a, that produced an unusual crystal type. Primary detection of parasporal inclusions using a phase contrast microscope presented one to two small crystal proteins in the sporulating cells of Bt-S84-13a. Compound light microscopic examination of autolysed Bt-S84-13a cells stained with 0.133% Coomassie Brilliant Blue showed two types of crystal morphology: small crystals independent of spores and spore-associated crystals. Surface structure analysis with a scanning electron microscope revealed spherical-like, coarse and wrinkled-looking crystal in Bt-S84-13a. A close-up observation of the crystal morphology using a transmission electron microscope also demonstrated two parasporal inclusions in Bt-S84-13a. One inclusion was deposited against the forespore and was in a shape of incomplete rectangular. Another smaller inclusion was developed within the exosporium and was rectangular in shape. However, the latter inclusion was found lack in another bacterial cell which was still in the early stages of sporulation. This unique crystal morphology may imply some biological potential in Bt-S84-13a.

Bacillus thuringiensis DB27 produces two novel protoxins, Cry21Fa1 and Cry21Ha1, which act synergistically against nematodes

Bacillus thuringiensis has been widely used as a biopesticide, primarily for the control of insect pests, but some B. thuringiensis strains specifically target nematodes. However, nematicidal virulence factors of B. thuringiensis are poorly investigated. Here, we describe virulence factors of nematicidal B. thuringiensis DB27 using Caenorhabditis elegans as a model. We show that B. thuringiensis DB27 kills a number of free-living and animal-parasitic nematodes via intestinal damage. Its virulence factors are plasmid-encoded Cry protoxins, since plasmid-cured derivatives do not produce Cry proteins and are not toxic to nematodes. Whole-genome sequencing of B. thuringiensis DB27 revealed multiple potential nematicidal factors, including several Cry-like proteins encoded by different plasmids. Two of these proteins appear to be novel and show high similarity to Cry21Ba1. Named Cry21Fa1 and Cry21Ha1, they were expressed in Escherichia coli and fed to C. elegans, resulting in intoxication, intestinal damage, and death of nematodes. Interestingly, the effects of the two protoxins on C. elegans are synergistic (synergism factor, 1.8 to 2.5). Using purified proteins, we determined the 50% lethal concentrations (LC50s) for Cry21Fa1 and Cry21Ha1 to be 13.6 μg/ml and 23.9 μg/ml, respectively, which are comparable to the LC50 of nematicidal Cry5B. Finally, we found that signaling pathways which protect C. elegans against Cry5B toxin are also required for protection against Cry21Fa1. Thus, B. thuringiensis DB27 produces novel nematicidal protoxins Cry21Fa1 and Cry21Ha1 with synergistic action, which highlights the importance of naturally isolated strains as a source of novel toxins.

Bacillus thuringiensis as a surrogate for Bacillus anthracis in aerosol research

Characterization of candidate surrogate spores prior to experimental use is critical to confirm that the surrogate characteristics are as closely similar as possible to those of the pathogenic agent of interest. This review compares the physical properties inherent to spores of Bacillus anthracis (Ba) and Bacillus thuringiensis (Bt) that impact their movement in air and interaction with surfaces, including size, shape, density, surface morphology, structure and hydrophobicity. Also evaluated is the impact of irradiation on the physical properties of both Bacillus species. Many physical features of Bt and Ba have been found to be similar and, while Bt is considered typically non-pathogenic, it is in the B. cereus group, as is Ba. When cultured and sporulated under similar conditions, both microorganisms share a similar cylindrical pellet shape, an aerodynamic diameter of approximately 1 μm (in the respirable size range), have an exosporium with a hairy nap, and have higher relative hydrophobicities than other Bacillus species. While spore size, morphology, and other physical properties can vary among strains of the same species, the variations can be due to growth/sporulation conditions and may, therefore, be controlled. Growth and sporulation conditions are likely among the most important factors that influence the representativeness of one species, or preparation, to another. All Bt spores may, therefore, not be representative of all Ba spores. Irradiated spores do not appear to be a good surrogate to predict the behavior of non-irradiated spores due to structural damage caused by the irradiation. While the use of Bt as a surrogate for Ba in aerosol testing appears to be well supported, this review does not attempt to narrow selection between Bt strains. Comparative studies should be performed to test the hypothesis that viable Ba and Bt spores will behave similarly when suspended in the air (as an aerosol) and to compare the known microscale characteristics versus the macroscale response.

Molecular Characterization of Novel Serovars of Bacillus thuringiensis Isolates from India

Novel Bacillus thuringiensis isolates GS4, GN24 and UP1 were isolated and characterized by determination of serotyping, insecticidal protein by SDS-PAGE, plasmid composition, cry gene content and insect toxicity. Serologically two isolates GS4 and UP1 were allocated to the H3abce which is a new serovar while isolate GN24 was of H3ab type. Isolate GS4 produced flat crystal inclusions while UP1 produced cuboidal crystals. PCR analysis found that both isolates contained cry1 and cry1Ac genes. The major protein bands found of isolate GS4 were of molecular weights 175, 135, 97, 88, 66, 54 and 27 kDa, isolate UP1 were of 85, 60 and 40 kDa and isolate GN24 were of 130, 90, 66 and 45 kDa. Though isolates GS4 and UP1 belonged to a new serovar H3abce, they showed different crystal inclusions and cry gene content. Isolate GS4 was toxic to lepidopteran insect larvae of Helicoverpa armigera but UP1 did not showed any toxicity.

A novel Bacillus thuringiensis Cry-like protein from a rare filamentous strain promotes crystal localization within the exosporium

Mutation of a novel cry-like gene (cry256) from Bacillus thuringiensis resulted in a protein crystal, normally located within the spore's exosporium, being found predominately outside the exosporium. The cry256 gene codes for a 3-domain Cry-like protein that does not correspond to any of the known Cry protein holotypes.

Gene clusters located on two large plasmids determine spore crystal association (SCA) in Bacillus thuringiensis subsp. finitimus strain YBT-020

Crystals in Bacillus thuringiensis are usually formed in the mother cell compartment during sporulation and are separated from the spores after mother cell lysis. In a few strains, crystals are produced inside the exosporium and are associated with the spores after sporulation. This special phenotype, named ‘spore crystal association’ (SCA), typically occurs in B. thuringiensis subsp. finitimus. Our aim was to identify genes determining the SCA phenotype in B. thuringiensis subsp. finitimus strain YBT-020. Plasmid conjugation experiments indicated that the SCA phenotype in this strain was tightly linked with two large plasmids (pBMB26 and pBMB28). A shuttle bacterial artificial chromosome (BAC) library of strain YBT-020 was constructed. Six fragments from BAC clones were screened from this library and discovered to cover the full length of pBMB26; four others were found to cover pBMB28. Using fragment complementation testing, two fragments, each of approximately 35 kb and located on pBMB26 and pBMB28, were observed to recover the SCA phenotype in an acrystalliferous mutant, B. thuringiensis strain BMB171. Furthermore, deletion analysis indicated that the crystal protein gene cry26Aa from pBMB26, along with five genes from pBMB28, were indispensable to the SCA phenotype. Gene disruption and frame-shift mutation analyses revealed that two of the five genes from pBMB28, which showed low similarity to crystal proteins, determined the location of crystals inside the exosporium. Gene disruption revealed that the three remaining genes, similar to spore germination genes, contributed to the stability of the SCA phenotype in strain YBT-020. Our results thus identified the genes determining the SCA phenotype in B. thuringiensis subsp. finitimus.

Complete genome sequence of Bacillus thuringiensis serovar finitimus strain YBT-020

Bacillus thuringiensis is a gram-positive, spore-forming bacterium that forms parasporal crystals at the onset of the sporulation phase of its growth. Here, we report the complete genome sequence of B. thuringiensis serovar finitimus strain YBT-020, whose parasporal crystals consist of Cry26Aa and Cry28Aa crystal proteins and are located between the exosporium and the spore coat and remain adhering to the spore after sporulation.

Detection of new cry genes of Bacillus thuringiensis by use of a novel PCR primer system

On the basis of the known cry gene sequences of Bacillus thuringiensis, three sets of primers were designed from four conserved blocks found in the delta-endotoxin-coding region. The primer pairs designed amplify the regions between blocks 1 and 5, 2 and 5, and 1 and 4. In silico analyses indicated that 100% of the known three-domain cry gene sequences can be amplified by these sets of primers. To test their ability to amplify known and unknown cry gene sequences, 27 strains from the CINVESTAV (LBIT series) collection showing atypical crystal morphology were selected. Their DNA was used as the template with the new primer system, and after a systematic amplification and sequencing of the amplicons, each strain showed one or more cry-related sequences, totaling 54 different sequences harbored by the 27 strains. Seven sequences were selected on the basis of their low level of identity to the known cry sequences, and once cloning and sequencing of the complete open reading frames were done, three new cry-type genes (primary ranks) were identified and the toxins that they encode were designated Cry57Aa1, Cry58Aa1, and Cry59Aa1 by the B. thuringiensis Toxin Nomenclature Committee. The rest of the seven sequences were classified Cry8Ka2, Cry8-like, Cry20Ba1, and Cry1Ma1 by the committee. The crystal morphology of the selected strains and analysis of the new Cry protein sequences showed interesting peculiarities.

Biochemical and molecular characterization of delta-endotoxins in Bacillus thuringiensis

The delta-endotoxins (delta-ETX) of four native strains (RT7, RT19, RT25, and RT25), and one reference strain (4L1) of Bacillus thuringiensis were biochemically and molecularly characterized to determine their potential toxic activity against lepidopteran larvae. Crystals of delta-ETX were purified through a two-phase system to determine their morphology, molar mass, solubility, and resistance to proteinases. Toxic activity and cry gene content were also determined. Crystals from native strains exhibited polyhedral, irregular and cuboidal shapes, while those from 4L1 were bipyramidal. Seven proteins with estimated molar mass approximately 30-134 kDa were detected as the main components of the native delta-ETX. Only crystals from 4L1, RT24, and RT25 underwent complete solubilization at pH >12.0. Crystals from all strains produced trypsin-resistant peptides. None of the cry genes associated with toxicity in lepidopterans (cry1, cry2, cry9) was found in the native strains; however, 4L1 strain harbors cry1 and cry2 genes. Strains RT19 and RT25 caused significant mortality against Trichoplusia ni larvae with partial solubilization at pH 10, strain 4L1 caused 100 % mortality. Toxicity of native strains may come from a novel cry gene.

Identification of thecrygene inBacillus thuringiensisstrain WZ-9 and its toxicity againstHenosepilachna vigintioctomaculata

Bacillus thuringiensisstrain WZ-9, isolated from soil in Hebei province, China, was effective againstHenosepilachna vigintioctomaculatalarvae. The strain presented bipyramidal crystals with a protein band of 130 kDa in SDS–PAGE. The pH changes of the culture media showed important fluctuations during the 24 h growth cycle. The pH varied less in log and stationary phases than it did in the exponential phase. Bioassay results showed that the WZ-9 strain was only harmful to larvae ofH. vigintioctomaculataand not to either adults ofH. vigintioctomaculataor other several lepidopteran and coleopteran insects. LC50to second-instar larvae ofH. vigintioctomaculatawas 2.95×107cells/ml after 72 h. Genotypic investigations showed that this strain possessed thecry7gene. Sequence analysis demonstrated that the encoding gene contained an open reading frame (ORF) of 3414 bp and encoded 1138 amino acid residues. The deduced amino acid sequence was 99.65% identical to that of the reported Cry7Ab2 sequences. This gene was designated by the Bt δ-endotoxin nomenclature committee as Cry7Ab3 with accession number BI 1015188 in the GenBank database.

The p53 pathway: positive and negative feedback loops

The p53 pathway responds to stresses that can disrupt the fidelity of DNA replication and cell division. A stress signal is transmitted to the p53 protein by post-translational modifications. This results in the activation of the p53 protein as a transcription factor that initiates a program of cell cycle arrest, cellular senescence or apoptosis. The transcriptional network of p53-responsive genes produces proteins that interact with a large number of other signal transduction pathways in the cell and a number of positive and negative autoregulatory feedback loops act upon the p53 response. There are at least seven negative and three positive feedback loops described here, and of these, six act through the MDM-2 protein to regulate p53 activity. The p53 circuit communicates with the Wnt-beta-catenin, IGF-1-AKT, Rb-E2F, p38 MAP kinase, cyclin-cdk, p14/19 ARF pathways and the cyclin G-PP2A, and p73 gene products. There are at least three different ubiquitin ligases that can regulate p53 in an autoregulatory manner: MDM-2, Cop-1 and Pirh-2. The meaning of this redundancy and the relative activity of each of these feedback loops in different cell types or stages of development remains to be elucidated. The interconnections between signal transduction pathways will play a central role in our understanding of cancer.

Identification and characterization of the new bacillus thuringiensis serovars pirenaica (serotype H57) and iberica (serotype H59)

Two new Bacillus thuringiensis strains have been classified by the H antigen of the cells and differentiated by their morphological, biochemical and molecular characteristics. The flagellar agglutination showed that both strains bore specific H antigens which allowed their classification as the new serotypes H57 and H59. The serovar names proposed for the type strains characterized in this work are B. thuringiensis ser. pirenaica, for the H serotype 57, and B. thuringiensis ser. iberica, for the H serotype 59. Further characterization of these strains, by means of SDS-PAGE, Western inmunodetection, plasmid profile and cry-gene identification by polymerase chain reaction, confirmed the originality of the two novel serotypes. Toxicity tests carried out against several insect species, belonging to the orders Lepidoptera, Diptera and Coleoptera, showed no detectable insecticidal activity for either of the B. thuringiensis strains.

Antagonism between Cry1Ac1 and Cyt1A1 toxins of bacillus thuringiensis

Most strains of the insecticidal bacterium Bacillus thuringiensis have a combination of different protoxins in their parasporal crystals. Some of the combinations clearly interact synergistically, like the toxins present in B. thuringiensis subsp. israelensis. In this paper we describe a novel joint activity of toxins from different strains of B. thuringiensis. In vitro bioassays in which we used pure, trypsin-activated Cry1Ac1 proteins from B. thuringiensis subsp. kurstaki, Cyt1A1 from B. thuringiensis subsp. israelensis, and Trichoplusia ni BTI-Tn5B1-4 cells revealed contrasting susceptibility characteristics. The 50% lethal concentrations (LC50s) were estimated to be 4,967 of Cry1Ac1 per ml of medium and 11.69 ng of Cyt1A1 per ml of medium. When mixtures of these toxins in different proportions were assayed, eight different LC50s were obtained. All of these LC50s were significantly higher than the expected LC50s of the mixtures. In addition, a series of bioassays were performed with late first-instar larvae of the cabbage looper and pure Cry1Ac1 and Cyt1A1 crystals, as well as two different combinations of the two toxins. The estimated mean LC50 of Cry1Ac1 was 2.46 ng/cm2 of diet, while Cyt1A1 crystals exhibited no toxicity, even at very high concentrations. The estimated mean LC50s of Cry1Ac1 crystals were 15.69 and 19.05 ng per cm2 of diet when these crystals were mixed with 100 and 1,000 ng of Cyt1A1 crystals per cm2 of diet, respectively. These results indicate that there is clear antagonism between the two toxins both in vitro and in vivo. Other joint-action analyses corroborated these results. Although this is the second report of antagonism between B. thuringiensis toxins, our evidence is the first evidence of antagonism between toxins from different subspecies of B. thuringiensis (B. thuringiensis subsp. kurstaki and B. thuringiensis subsp. israelensis) detected both in vivo and in vitro. Some possible explanations for this relationship are discussed.