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

Bacillus thuringiensis Bt_UNVM-84, a Novel Strain Showing Insecticidal Activity against Anthonomus grandis Boheman (Coleoptera: Curculionidae)

Bacillus thuringiensis is a Gram-positive bacterium known for its insecticidal proteins effective against various insect pests. However, limited strains and proteins target coleopteran pests like Anthonomous grandis Boheman, causing substantial economic losses in the cotton industry. This study focuses on characterizing a Bacillus sp. strain, isolated from Oncativo (Argentina), which exhibits ovoid to amorphous parasporal crystals and was designated Bt_UNVM-84. Its genome encodes genes for the production of two pairs of binary Vpb1/Vpa2 proteins and three Cry-like proteins showing similarity with different Cry8 proteins. Interestingly, this gene content was found to be conserved in a previously characterized Argentine isolate of B. thuringiensis designated INTA Fr7-4. SDS-PAGE analysis revealed a major band of 130 kDa that is proteolytically processed to an approximately 66-kDa protein fragment by trypsin. Bioassays performed with spore-crystal mixtures demonstrated an interesting insecticidal activity against the cotton boll weevil A. grandis neonate larvae, resulting in 91% mortality. Strain Bt_UNVM-84 is, therefore, an interesting candidate for the efficient biological control of this species, causing significant economic losses in the cotton industry in the Americas.

Molecular and Toxicological Characterization of a Bacillus thuringiensis Strain Expressing a Vip3 Protein Highly Toxic to Spodoptera frugiperda (Lepidoptera: Noctuidae)

The characterization of the Bacillus thuringiensis (Berliner) LBIT-418 strain was based on a previous work which indicated its high insecticidal potential. Therefore, toxicological, molecular, and biochemical characterizations were conducted in this work to identify its unique features and its potential to be developed as a bioinsecticide. This strain, originally isolated from a healthy mosquito larva, was identified within the subspecies kenyae by sequencing of the hag gene and by the multilocus sequence typing (MLST) technique. Genes cry1Ac2, cry1Ea3, cry2Aa1 and cry2Ab4, and a cry1Ia were detected in its genome, in addition to a vip3Aa gene. In this research, the latter protein was successfully cloned, expressed, and purified and showed high toxicity towards the fall armyworm, Spodoptera frugiperda (J.E. Smith), fourth instar larvae in bioassays using the microdroplet ingestion technique, estimating an LD50 of 21.38 ng/larva. Additional bioassays were performed using the diet surface inoculation technique of the strain's spore-crystal complex against diamondback moth larvae, Plutella xylostella (Linnaeus), estimating an LC50 of 10.22 ng/cm2. Its inability to produce β-exotoxin was demonstrated by bioassays against the nematode Caenorhabditis elegans Maupas and by HPLC analysis. These results support the high potential of this strain to be developed as a bioinsecticide.

Molecular Characterization of Native Bacillus thuringiensis Strains from Root Nodules with Toxicity Against the Fall Armyworm (FAW, Spodoptera frugiperda) and Brinjal Ash Weevil (Myllocerus subfasciatus)

The fall armyworm is an exotic pest which destroys a wide variety of crops Querywhereas the brinjal ash weevil is a serious pest of eggplant and other solanaceous vegetables. The goal of this research is to find a sustainable and ecologically friendly bio-control agent for managing FAW and brinjal ash weevils. Twelve natural Bacillus thuringiensis strains were isolated from cowpea root nodules, and the Gram-positive cells with characteristic Bt crystal structures were discovered using phase contrast and scanning electron microscopy. There were bipyramidal, cuboidal, rhombus, and spherical crystals. The Bt cry gene content was characterized by PCR analysis, which revealed the presence of cry1, cry1I, cry3, cry7, cry7,8, cry14, cry26, and cry55 genes. The identity of Bt was confirmed by cloning and sequencing the cry genes. In the nucleotide sequences, no pseudo genes or indels were found in cry sequences. SDS-PAGE examination indicated the presence of bands ranging in size from 13 to 130 kDa, with 50-60 kDa being the most common. When compared to the control, the new native Bt strains were lethal, with pathogenicity ranging from 93 to 100% against S. frugiperda larvae and M. subfasciatus adults. The studies revealed that the native strains with conserved regions of 16S rRNA genes were compared to NCBI database sequences and classified as native Bt strains with 99-100% similarity to known Bt strains. In conclusion, native Bt strains from cowpea root nodules were shown to have bio-insecticidal activity against fall armyworm larvae and brinjal ash weevil adults.

The Combination Analysis Between Bacillus thuringiensis Sip1Ab Protein and Brush Border Membrane Vesicles in Midgut of Colaphellus bowringi Baly

The secretory insecticidal protein Sip1Ab and crystal protein Cry8Ca from Bacillus thuringiensis (Bt) are widely recognized for their coleopteran insecticidal activities. It is worthwhile to investigate the insecticidal mechanisms of these two proteins against Colaphellus bowringi Baly, which is a serious pest of cruciferous vegetables in China and other Asian countries. To that end, the genes encoding the Sip1Ab and Cry8Ca proteins were amplified from the strain QZL38 genome, then expressed in Escherichia coli, after which bioassays were conducted in C. bowringi larvae. After feeding these two proteins, the histopathological changes in the midguts of C. bowringi larvae were observed using transmission electron microscopy (TEM), and the Brush Border Membrane Vesicle (BBMV) was extracted for competition binding assays. TEM showed that ingestion of Sip1Ab caused a significant reduction in growth of the larvae, disruption of midgut microvilli, and expansion of intercellular spaces. Competition binding assays demonstrated that Sip1Ab bound to C. bowringi BBMV with a high binding affinity. However, a mixture of the two proteins in equal proportions showed no significant difference in insecticidal activity from that of Sip1Ab. These results could provide a molecular basis for the application of Sip1Ab in coleopteran insect control and contribute to the study of the Sip1Ab insecticidal mechanism as well.

Whole genome analysis and functional characterization of a novel Bacillus thuringiensis (Bt 62) isolate against sugarcane white grub Holotrichia serrata (F)

In this study, we report the whole genome assembly of Bt 62, a novel isolate harbouring cry8 holotype gene identified by us earlier. Sequencing was carried out using a combination of Illumina NextSeq 500 and Oxford Nanopore sequencing Technologies (ONT). The final assembled genome was 6.13 Mb comprising a circular chromosome and four plasmids. The bioassay studies against Holotrichia serrata (F.) (Coleoptera: Scarabaeidae), a polyphagous pest infesting sugarcane and other crops, indicated significant toxicity to first instar grubs over untreated larvae achieving a highest mean mortality of 91.11% for various doses tested. In vitro proteolytic assay and histopathological studies of the midgut of infected white grubs revealed proteolytic processing of the protoxin and extensive degeneration of larval midgut epithelial cells. The results demonstrate that this novel isolate could be used as a biopesticide or its crystal toxin genes could be expressed in sugarcane and other crops for resistance against H. serrata.

Identification and characterization of a new cry-like gene found in a Bacillus cereus strain

Bacillus thuringiensis is the most successful microbial insecticide against different pests in agriculture and vectors of diseases. Its activity is mostly attributed to the Cry proteins expressed during its sporulation phase. However, these proteins are not exclusive to B. thuringiensis. Some cry genes have been found in other Bacillus species, or even in other genera. In this work, cry genes were searched in 223 acrystalliferous bacillaceous strains. From these strains 13 amplicons were obtained, cloned, and sequenced; however, only 6 amplicons tested positive for cry-like genes, and the 6 isolates showed to be the same strain. We report the characterization of an unusual strain of B. cereus (LBIC-004) which is unable to form protein inclusions during the sporulation phase. LBIC-004 showed a high identity to B. cereus using the sequences of 16S rRNA, gyrB and hag genes; in addition, a unique plasmid pattern of the strain was obtained. A 1953-bp cry gene was identified, coding for a 651 amino acid protein with a molecular weight of 74.9 kDa. This protein showed a predicted three-domain structure, similar to all Cry proteins. However, the amino acid sequence of the protein showed only 41% identity its highest hit: the Cry8Ca1 protein, indicating the uniqueness of this cry-like gene. It was cloned and transferred into a mutant acrystalliferous B. thuringiensis strain which was used in bioassays against Caenorhabditis elegans, Aedes aegypti, Manduca sexta and Phyllophaga sp. The recombinant strain showed no crystal formation and no toxicity to the tested species.

ORFograph: search for novel insecticidal protein genes in genomic and metagenomic assembly graphs

BACKGROUND

Since the prolonged use of insecticidal proteins has led to toxin resistance, it is important to search for novel insecticidal protein genes (IPGs) that are effective in controlling resistant insect populations. IPGs are usually encoded in the genomes of entomopathogenic bacteria, especially in large plasmids in strains of the ubiquitous soil bacteria, Bacillus thuringiensis (Bt). Since there are often multiple similar IPGs encoded by such plasmids, their assemblies are typically fragmented and many IPGs are scattered through multiple contigs. As a result, existing gene prediction tools (that analyze individual contigs) typically predict partial rather than complete IPGs, making it difficult to conduct downstream IPG engineering efforts in agricultural genomics.

METHODS

Although it is difficult to assemble IPGs in a single contig, the structure of the genome assembly graph often provides clues on how to combine multiple contigs into segments encoding a single IPG.

RESULTS

We describe ORFograph, a pipeline for predicting IPGs in assembly graphs, benchmark it on (meta)genomic datasets, and discover nearly a hundred novel IPGs. This work shows that graph-aware gene prediction tools enable the discovery of greater diversity of IPGs from (meta)genomes.

CONCLUSIONS

We demonstrated that analysis of the assembly graphs reveals novel candidate IPGs. ORFograph identified both already known genes "hidden" in assembly graphs and potential novel IPGs that evaded existing tools for IPG identification. As ORFograph is fast, one could imagine a pipeline that processes many (meta)genomic assembly graphs to identify even more novel IPGs for phenotypic testing than would previously be inaccessible by traditional gene-finding methods. While here we demonstrated the results of ORFograph only for IPGs, the proposed approach can be generalized to any class of genes. Video abstract.

Selection and characterization of two Bacillus thuringiensis strains showing nematicidal activity against Caenorhabditis elegans and Meloidogyne incognita

Bacillus thuringiensis has been widely used as a biological control agent against insect pests. Additionally, nematicidal strains have been under investigation. In this report, 310 native strains of B. thuringiensis against Caenorhabditis elegans were tested. Only the LBIT-596 and LBIT-107 strains showed significant mortality. LC50s of spore-crystal complexes were estimated at 37.18 and 31.89 μg/mL for LBIT-596 and LBIT-107 strains, respectively, while LC50s of partially purified crystals was estimated at 23.76 and 20.25 μg/mL for LBIT-596 and LBIT-107, respectively. The flagellin gene sequence and plasmid patterns indicated that LBIT-596 and LBIT-107 are not related to each other. Sequences from internal regions of a cry5B and a cyt1A genes were found in the LBIT-596 strain, while a cry21A, a cry14A and a cyt1A genes were found in the LBIT-107 strain. Genome sequence of the LBIT-107 strain showed new cry genes, along with other virulence factors, hence, total nematicidal activity of the LBIT-107 strain may be the result of a multifactorial effect. The highlight of this contribution is that translocation of spore-crystal suspensions of LBIT-107 into tomato plants inoculated at their rhizosphere decreased up to 90% the number of galls of Meloidogyne incognita, perhaps the most important nematode pest in the world.

Exploration of insecticidal potential of Cry protein purified from Bacillus thuringiensis VIID1

Insect pests are a threat to agriculture as they cause a loss of 15-22% to economically important crops every year. Bacillus thuringiensis produces parasporal crystal inclusions that have insecticidal 'Cry' proteins which are toxic to insect larvae of the order Lepidoptera, Coleoptera and Diptera, etc. In the present study, 40 different soil samples from Amritsar and its surrounding areas were selected for isolation of B. thuringiensis. The rod shaped, gram-positive bacterial isolates were further analyzed for characteristic crystal formation using phase contrast and scanning electron microscopy. 6 Bacillus samples containing cry genes were identified using the universal primers for cry genes, of which one isolate exhibited a protein band of ~95 kDa. This protein was purified using a Sephadex G-75 column. The insecticidal assays conducted with purified Cry protein on insect larvae of lepidopteran and dipteran orders viz. Spodoptera litura, Galleria malonella, Bactrocera cucurbitae and Culex pipens revealed considerable detrimental effects. A significant increase in larval mortality was observed for the larvae of all insects in a concentration dependent manner when treated with Cry protein purified from B. thuringenisis VIID1. The purified Cry protein did not have any significant effect on honey bee larvae.

Insecticidal Activity of a Cry1Ca toxin of Bacillus thuringiensis Berliner (Firmicutes: Bacillaceae) and Its Synergism with the Cyt1Aa Toxin Against Aedes aegypti (Diptera: Culicidae)

The Cry1C protein family of Bacillus thuringiensis form bipyramidal crystals, which are commonly associated with toxic activity against lepidopteran species; however, some members of this family may also be toxic to dipterans. In the present work, the Cry1Ca16 protein, synthesized by the B. thuringiensis LBIT-1217 strain, was analyzed. The gene coding for this protein was amplified, sequenced, and cloned into the pSTAB vector, which was electro-transferred into the acrystalliferous B. thuringiensis 4Q7 strain. The recombinant strain showed the expected bipyramidal crystal morphology, identical to the original LBIT-1217 strain and exhibited toxicity against larvae of Aedes aegypti (Diptera). Pure crystals from the recombinant strain were used in bioassays against Ae. aegypti larvae, estimating an LC50 of 4.61 μg/ml. Further studies on Cry1Ca16 mosquitocidal potential included joint-action tests with the Cyt1Aa protein crystals from B. thuringiensis israelensis. An LC50 using pure Cyt1Aa crystals was estimated at 0.73 μg/ml, whereas an LC50 of 0.61 μg/ml was estimated when both toxins were tested together. Data from these bioassays was analyzed using joint-action tests such as the Tammes-Bakuniak graphical method and the formula proposed by Tabashnik (1992). Both tests clearly showed a synergistic effect between these two toxins.

Toxicity evaluation of Aphidicidal crystalliferous toxins from Bacillus thuringiensis strains: a molecular study

Purpose

Aphis gossypii and A. punicae are the most damaging pests. The emergence of large populations has created concern among farmers because this pest complex is considered critical as it has a significant effect on major crops around the globe. The lack of new technologies for the control of A. gossypii and A. punicae is also worrying due to the indiscriminate use of chemical insecticides. Besides, this leads to the rapid development of resistance, which strangles their control in the field. Hence, there is a dire need to find the effective biocontrol agent for the management of Aphis gossypii and A. punicae.

Methods

The present investigation emphasizes the isolation and characterization of Aphidicidal Bacillus thuringiensis from the Andaman and Nicobar Islands, Karnataka, Assam, Arunachal Pradesh, and Sikkim soil samples. Phase contrast and scanning electron microscopy analysis used to characterize and identify the crystal morphology. Molecular profiling of Bt cry genes was determined by PCR using aphidicidal cry gene-specific primers, and molecular cloning and sequencing were carried out. Protein profiling by SDS–PAGE analysis was further studied. Finally, a qualitative bioassay of insecticidal activity was carried out against A. gossypii and A. punicae.

Results

A total of 65 Bacillus-like colonies were screened; 15 putative Aphidicidal B. thuringiensis isolates were identified based on morphological as well as through microbiological studies. Spherical and amorphous crystal inclusion was predominantly present in 34.28% of the Bt isolates. Crystal protein profiling of Bt isolates by SDS–PAGE analysis showed the presence 130, 73, 34, 25, and 13 kDa bands, among which 50−66 kDa bands were present abundantly. The detection of the cry gene of these isolates was done by PCR analysis, which indicated that cry1, cry2A, cry3A, and cry11A were on plasmid DNA. All cry genes were 80–100% homologous when aligned on alignment tool NCBI-BLASTn and BLASTp. All isolates of Bt were tested for their insecticidal activity against aphids. Three of the 15 isolates are Aphidicidal toxin specific by PCR analysis which were observed to be toxic to Aphis gossypii and A. punicae at a concentration of 35 μg/mL. The observed physical changes were induced by B. thuringiensis infection; these strains had been re-isolated from the dead aphids, and the presented results fulfilled Koch’s postulates.

Conclusion

The present study brought promising Bt isolates, primarily capable of creating an efficient biocontrol agent for Aphis gossypii and A. punicae and various sucking pests soon.

Advanced Methods for Detection of Bacillus cereus and Its Pathogenic Factors

Bacillus cereus is an opportunistic foodborne pathogen causing food intoxication and infectious diseases. Different toxins and pathogenic factors are responsible for diarrheal syndrome, like nonhemolytic enterotoxin Nhe, hemolytic enterotoxin Hbl, enterotoxin FM and cytotoxin K, while emetic syndrome is caused by the depsipeptide cereulide toxin. The traditional method of B. cereus detection is based on the bacterial culturing onto selective agars and cells enumeration. In addition, molecular and chemical methods are proposed for toxin gene profiling, toxin quantification and strain screening for defined virulence factors. Finally, some advanced biosensors such as phage-based, cell-based, immunosensors and DNA biosensors have been elaborated to enable affordable, sensitive, user-friendly and rapid detection of specific B. cereus strains. This review intends to both illustrate the state of the B. cereus diagnostic field and to highlight additional research that is still at the development level.

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.

Toxicity of Cry2 proteins from Bacillus thuringiensis subsp. thuringiensis strain T01-328 against Aedes aegypti (Diptera: Culicidae)

ABSTRACT: Bacillus thuringiensis subsp. israelensis has been used to control the Aedes aegypti (Diptera: Culicidae) mosquito larvae, the vector of virus diseases such as dengue, Chikungunya and Zika fever, which have become a major public health problem in Brazil and other tropical countries since the climate favors the proliferation and development of the transmitting vector. Because B. thuringiensis has shown potential for controlling insects of the Diptera order, this work aimed at testing the Bacillus thuringiensis subsp. thuringiensis strain T01-328 and its proteins Cry2Aa and Cry2Ab for control A. aegypti and at comparing the results to the B. thuringiensis subsp. israelensis specific dipteran strain. To this end, bioassays using spore-crystal of both strains, and Cry2Aa and Cry2Ab proteins from the heterologous expression in Escherichia coli, were performed against A. aegypti larvae. The results showed that the B. thuringiensis thuringiensis T01-328 has insecticidal activity against the larvae, but it is less toxic than B. thuringiensis subsp. israelensis. Cry2Aa and Cry2Ab proteins expressed heterologously were effective for controlling A. aegypti larvae. Therefore, the results indicate that the Cry2Aa and Cry2Ab proteins of the B. thuringiensis thuringiensis T01-328 can be used as an alternative to assist in the control of A. aegypti.

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.

Lineage-specific plasmid acquisition and the evolution of specialized pathogens in Bacillus thuringiensis and the Bacillus cereus group

Bacterial plasmids can vary from small selfish genetic elements to large autonomous replicons that constitute a significant proportion of total cellular DNA. By conferring novel function to the cell, plasmids may facilitate evolution but their mobility may be opposed by co-evolutionary relationships with chromosomes or encouraged via the infectious sharing of genes encoding public goods. Here, we explore these hypotheses through large-scale examination of the association between plasmids and chromosomal DNA in the phenotypically diverse Bacillus cereus group. This complex group is rich in plasmids, many of which encode essential virulence factors (Cry toxins) that are known public goods. We characterized population genomic structure, gene content and plasmid distribution to investigate the role of mobile elements in diversification. We analysed coding sequence within the core and accessory genome of 190 B. cereus group isolates, including 23 novel sequences and genes from 410 reference plasmid genomes. While cry genes were widely distributed, those with invertebrate toxicity were predominantly associated with one sequence cluster (clade 2) and phenotypically defined Bacillus thuringiensis. Cry toxin plasmids in clade 2 showed evidence of recent horizontal transfer and variable gene content, a pattern of plasmid segregation consistent with transfer during infectious cooperation. Nevertheless, comparison between clades suggests that co-evolutionary interactions may drive association between plasmids and chromosomes and limit wider transfer of key virulence traits. Proliferation of successful plasmid and chromosome combinations is a feature of specialized pathogens with characteristic niches (Bacillus anthracis, B. thuringiensis) and has occurred multiple times in the B. cereus group.

Isolation and characterization of Bacillus thuringiensis strains native to Assam soil of North East India

We have identified both crystalliferous and acrystalliferous Bt isolates from the Assam soil of North East India for the first time. A total of 301 Bacillus type colonies were selected based on their appearance and colony morphology. Out of these colonies, 42 isolates had characteristics similar to Bt isolates on MYP (Mannitol Egg Yolk Polymyxin) agar base medium. The ERIC-PCR and 16S rDNA analyses confirmed that 42 isolates are Bacillus thuringiensis. Phase contrast microscopy showed that 37 isolates produced crystal endospore during the sporulation phase and 5 acrystalliferous isolates were also found. Amplification of cry gene was carried out using general Cry primers along with one cry2 gene specific primer. Out of 42 isolates, 50% of the isolates showed presence of cry2 gene followed by cry9 (40.47) and cry1 (40.47). Moreover, 21.42% of isolates showed the presence of more than one cry genes. We also screened these isolates for the possibility of having new Bt genes using universal primer and found two strains having a new type of Cry1I gene with 82 and 85% similarities with the available Cry1I gene sequences. Thus, these new types of Bt gene could be useful for Bt-based bioformulations and generation of transgenic plants.

Characterization of lepidopteran-specific cry1 and cry2 gene harbouring native Bacillus thuringiensis isolates toxic against Helicoverpa armigera

Bacillus thuringiensis (Bt) based biopesticides are feasible alternatives to chemical pesticides. Here, we present the distribution of lepidopteran-specific cry1 and cry2 genes in native B. thuringiensis. Forty four out of 86 colonies were found to harbour crystals by phase contrast microscopy exhibiting a Bt index of 0.51. PCR analysis resulted in the amplification of cry1 in 24 and cry2 in 14 isolates. Twelve of the isolates showed presence of both cry1 and cry2, while 18 isolates did not show presence of either of the genes. Toxicity screening using spore-crystal mixtures against 2nd instar larvae of Helicoverpa armigera revealed that the isolates (50%) were either mildly toxic or not toxic (36.36%), and only 13.63% were toxic. The results are interesting, particularly so because the same isolates were previously reported to contain lepidopteran specific vip3A genes also, hence can complement the toxicity of the isolates harbouring vip3A genes.

In Vivo Crystallization of Three-Domain Cry Toxins

Bacillus thuringiensis (Bt) is the most successful, environmentally-friendly, and intensively studied microbial insecticide. The major characteristic of Bt is the production of proteinaceous crystals containing toxins with specific activity against many pests including dipteran, lepidopteran, and coleopteran insects, as well as nematodes, protozoa, flukes, and mites. These crystals allow large quantities of the protein toxins to remain stable in the environment until ingested by a susceptible host. It has been previously established that 135 kDa Cry proteins have a crystallization domain at their C-terminal end. In the absence of this domain, Cry proteins often need helper proteins or other factors for crystallization. In this review, we classify the Cry proteins based on their requirements for crystallization.

Low-Dose Effects: Nonmonotonic Responses for the Toxicity of a Bacillus thuringiensis Biocide to Daphnia magna

Currently, there is a trend toward an increasing use of biopesticides assumed to be environmentally friendly, such as Bacillus thuringiensis (Bt). Studies of the Bt toxicity to nontarget organisms have reported low effects at high exposure levels, which is interpreted as indicating negligible risk to nontarget organisms. We investigated the response of the nontarget organism Daphnia magna to waterborne DiPel ES, a globally used Bt formulation. Neonates and adults were exposed for 48 h to a wide range of concentrations, and immobilization and mortality were monitored. Whole body biomarkers (body weight, protein, chitobiase, catalase, xenobiotic metabolism, and acetylcholinesterase) were measured in the adults. The immobilization and mortality of the neonates were affected in a nonmonotonic and inverted U-shaped pattern with EC₅₀s that were ∼10⁵-fold lower than those reported by the manufacturer. The immobilization of adults demonstrated a similar pattern, but significant mortality was not observed. The biomarker results revealed multiphasic dose-response curves, which suggested toxicity mechanisms that affected various physiological pathways. The main particle size in exposure media was in the size range of bacterial spores and crystal toxins. However, the chemical heterogeneity was nonmonotonic, with a change in the phase at the maximum of toxicity (∼5 μL L^-1), which might explain the observed nonmonotonic effects. These results demonstrate the vulnerability of a nontarget organism to a biopesticide that is considered to be safe, while challenging the universal applicability of the central ecotoxicological assumption of monotonicity.

Characterization of a highly toxic strain of Bacillus thuringiensis serovar kurstaki very similar to the HD-73 strain

The LBIT-1200 strain of Bacillus thuringiensis was recently isolated from soil, and showed a 6.4 and 9.5 increase in toxicity, against Manduca sexta and Trichoplusia ni, respectively, compared to HD-73. However, LBIT-1200 was still highly similar to HD-73, including the production of bipyramidal crystals containing only one protein of ∼130 000 kDa, its flagellin gene sequence related to the kurstaki serotype, plasmid and RepPCR patterns similar to HD-73, no production of β-exotoxin and no presence of VIP genes. Sequencing of its cry gene showed the presence of a cry1Ac-type gene with four amino acid differences, including two amino acid replacements in domain III, compared to Cry1Ac1, which may explain its higher toxicity. In conclusion, the LBIT-1200 strain is a variant of the HD-73 strain but shows a much higher toxicity, which makes this new strain an important candidate to be developed as a bioinsecticide, once it passes other tests, throughout its biotechnological development.

Insect Biotechnology

For the purpose of this work, insect biotechnology, which is also known as yellow biotechnology, is the use of insects as well as insect-derived cells or molecules in medical (red biotechnology), agricultural (green biotechnology), and industrial (white) biotechnology. It is based on the application of biotechnological techniques on insects or their cells to develop products or services for human use. Such products are then applied in agriculture, medicine, and industrial biotechnology. Insect biotechnology has proven to be a useful resource in diverse industries, especially for the production of industrial enzymes including chitinases and cellulases, pharmaceuticals, microbial insecticides, insect genes, and many other substances. Insect cells (ICs), and particularly lepidopteran cells, constitute a competitive strategy to mammalian cells for the manufacturing of biotechnology products. Among the wide range of methods and expression hosts available for the production of biotech products, ICs are ideal for the production of complex proteins requiring extensive posttranslational modification. The progress so far made in insect biotechnology essentially derives from scientific breakthroughs in molecular biology, especially with the advances in techniques that allow genetic manipulation of organisms and cells. Insect biotechnology has grown tremendously in the last 30 years.

Cry Proteins from Bacillus thuringiensis Active against Diamondback Moth and Fall Armyworm

Biopesticides based on Bacillus thuringiensis and genetically modified plants with genes from this bacterium have been used to control Plutella xylostella (L.) and Spodoptera frugiperda (J.E. Smith). However, the selection pressure imposed by these technologies may undermine the efficiency of this important alternative to synthetic insecticides. Toxins with different modes of action allow a satisfactory control of these insects. The purpose of this study was to characterize the protein and gene contents of 20 B. thuringiensis isolates from soil and insect samples collected in several areas of Northeast Brazil which are active against P. xylostella and S. frugiperda. Protein profiles were obtained by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Polymerase chain reaction assays were used to determine toxin genes present within bacterial isolates. The protein profile of the majority of the isolates produced bands of approximately 130 kDa, suggesting the presence of Cry1, Cry8 and Cry9 proteins. The gene content of the isolates of B. thuringiensis investigated showed different gene profiles. Isolates LIIT-4306 and LIIT-4311 were the most actives against both species, with LC50 of 0.03 and 0.02 × 10(8) spores mL(-1), respectively, for P. xylostella, and LC50 of 0.001 × 10(8) spores mL(-1) for S. frugiperda. These isolates carried the cry1, cry1Aa, cry1Ab, cry1Ac, cry1B, cry1C, cry1D, cry1F, cry2, cry2A, cry8, and cry9C genes. The obtained gene profiles showed great potential for the control of P. xylostella and S. frugiperda, primarily because of the presence of several cry1A genes, which are found in isolates of B. thuringiensis active against these insects.

Detection of toxin proteins from Bacillus thuringiensis strain 4.0718 by strategy of 2D-LC-MS/MS

Bacillus thuringiensis is a kind of insecticidal microorganism which can produce a variety of toxin proteins, it is particularly important to find an effective strategy to identify novel toxin proteins rapidly and comprehensively with the discovery of the wild-type strains. Multi-dimensional high-performance liquid chromatography combined with mass spectrometry has become one of the main methods to detect and identify toxin proteins and proteome of B. thuringiensis. In this study, protein samples from B. thuringiensis strain 4.0718 were analyzed on the basis of two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS), and tryptic peptides of whole cell from the late sporulation phase were eluted at different concentration gradients of ammonium chloride and followed by secondary mass spectrum identification. 831 and 894 proteins were identified from two biological replicates, respectively, while 1,770 and 1,859 peptides were detected correspondingly. Among the identified proteins and peptides, 606 proteins and 1,259 peptides were detected in both replicates, which mean that 1,119 proteins and 2,370 peptides were unique to the proteome of this strain. A total of 15 toxins have been identified successfully, and seven of them were firstly discovered in B. thuringiensis strain 4.0718 that were Crystal protein (A1E259), pesticidal protein (U5KS09), Cry2Af1 (A4GVF0), Cry2Ad (Q9RM89), Cry1 (K4HMB5), Cry1Bc (Q45774), and Cry1Ga (Q45746). The proteomic strategy employed in the present study has provided quick and exhaustive identification of toxins produced by B. thuringiensis.

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.

Cloning and characterization of a novel cry8Ab1 gene from Bacillus thuringiensis strain B-JJX with specific toxicity to scarabaeid (Coleoptera: Scarabaeidae) larvae

Isolation of Bacillus thuringiensis (Bt) strain or its cry gene encoding insecticidal crystal protein (ICP) with specific toxicity is of great importance to biological control of insect pests. In this study, by screening 66 strains of Bt isolated from soil samples collected in Shandong Province, China, a new cry8-type gene from Bt strain B-JJX was identified via PCR-RFLP method. This novel gene, cry8Ab1, was cloned from the Bt strain B-JJX and expressed in an acrystalliferous mutant strain HD-73(-). The open reading frame of the cry8Ab1 gene consists of 3543bp with a G+C content of 37.99% and encodes a protein of 1180 amino acids with a putative MW of 133.3kDa which was confirmed by SDS-PAGE analysis. The Cry8Ab1 protein was expressed and released as spherical parasporal crystals from Bt acrystalliferous mutant strain HD-73(-) along with the presence of spores. In bioassays, this protein was toxic to 3-day-old larvae of the scarabaeid pests, Holotrichia oblita and H. parallela, with an LC50 of 5.72 and 2.00μgtoxing(-1)soil, respectively. The results are in accordance with the insecticidal activities of the original Bt strain B-JJX, which had an LC50 of 1.72 and 0.96μgtoxing(-1)soil against H. oblita and H. parallela, respectively.

Mining new crystal protein genes from Bacillus thuringiensis on the basis of mixed plasmid-enriched genome sequencing and a computational pipeline

We have designed a high-throughput system for the identification of novel crystal protein genes (cry) from Bacillus thuringiensis strains. The system was developed with two goals: (i) to acquire the mixed plasmid-enriched genomic sequence of B. thuringiensis using next-generation sequencing biotechnology, and (ii) to identify cry genes with a computational pipeline (using BtToxin_scanner). In our pipeline method, we employed three different kinds of well-developed prediction methods, BLAST, hidden Markov model (HMM), and support vector machine (SVM), to predict the presence of Cry toxin genes. The pipeline proved to be fast (average speed, 1.02 Mb/min for proteins and open reading frames [ORFs] and 1.80 Mb/min for nucleotide sequences), sensitive (it detected 40% more protein toxin genes than a keyword extraction method using genomic sequences downloaded from GenBank), and highly specific. Twenty-one strains from our laboratory's collection were selected based on their plasmid pattern and/or crystal morphology. The plasmid-enriched genomic DNA was extracted from these strains and mixed for Illumina sequencing. The sequencing data were de novo assembled, and a total of 113 candidate cry sequences were identified using the computational pipeline. Twenty-seven candidate sequences were selected on the basis of their low level of sequence identity to known cry genes, and eight full-length genes were obtained with PCR. Finally, three new cry-type genes (primary ranks) and five cry holotypes, which were designated cry8Ac1, cry7Ha1, cry21Ca1, cry32Fa1, and cry21Da1 by the B. thuringiensis Toxin Nomenclature Committee, were identified. The system described here is both efficient and cost-effective and can greatly accelerate the discovery of novel cry genes.

Rapid detection of vip1-type genes from Bacillus cereus and characterization of a novel vip binary toxin gene

A PCR-restriction fragment length polymorphism (PCR-RFLP) method for identifying vegetative insecticidal protein (vip) 1-type genes from Bacillus cereus was developed by designing specific primers based on the conserved regions of the genes to amplify vip1-type gene fragments. PCR products were digested with endonuclease AciI, and four known vip1-type genes were identified. Vip1Ac and vip1Aa-type genes appeared in 17 of 26 B. cereus strains. A novel vip1-type gene, vip1Ac1, was identified from B. cereus strain HL12. The vip1Ac1 and vip2Ae3 genes were co-expressed in Escherichia coli strain BL21 by vector pCOLADuet-1. The binary toxin showed activity only against Aphis gossypii (Homoptera), but not for Coleptera (Tenebrio molitor, Holotrichia oblita), Lepidoptera (Spodoptera exigua, Helicoverpa armigera, and Chilo suppressalis), Diptera (Culex quinquefasciatus). The LC(50) of this binary toxin for A. gossypii is 87.5 (34.2-145.3) ng mL(-1) . This is probably only the second report that Vip1 and Vip2 binary toxin shows toxicity against homopteran pests. The PCR-RFLP method developed could be very useful for identifying novel Vip1-Vip2-type binary toxins, and the novel binary toxins, Vip1Ac1 and Vip2Ae3, identified in this study may have applications in biological control of insects, thus avoiding potential problems of resistance.

Rapidly progressive, fatal, inhalation anthrax-like infection in a human: case report, pathogen genome sequencing, pathology, and coordinated response

CONTEXT

Ten years ago a bioterrorism event involving Bacillus anthracis spores captured the nation's interest, stimulated extensive new research on this pathogen, and heightened concern about illegitimate release of infectious agents. Sporadic reports have described rare, fulminant, and sometimes fatal cases of pneumonia in humans and nonhuman primates caused by strains of Bacillus cereus , a species closely related to Bacillus anthracis.

OBJECTIVES

To describe and investigate a case of rapidly progressive, fatal, anthrax-like pneumonia and the overwhelming infection caused by a Bacillus species of uncertain provenance in a patient residing in rural Texas.

DESIGN

We characterized the genome of the causative strain within days of its recovery from antemortem cultures using next-generation sequencing and performed immunohistochemistry on tissues obtained at autopsy with antibodies directed against virulence proteins of B anthracis and B cereus.

RESULTS

We discovered that the infection was caused by a previously unknown strain of B cereus that was closely related to, but genetically distinct from, B anthracis . The strain contains a plasmid similar to pXO1, a genetic element encoding anthrax toxin and other known virulence factors. Immunohistochemistry demonstrated that several homologs of B anthracis virulence proteins were made in infected tissues, likely contributing to the patient's death.

CONCLUSIONS

Rapid genome sequence analysis permitted us to genetically define this strain, rule out the likelihood of bioterrorism, and contribute effectively to the institutional response to this event. Our experience strongly reinforced the critical value of deploying a well-integrated, anatomic, clinical, and genomic strategy to respond rapidly to a potential emerging, infectious threat to public health.