New strategy for identification of novel Cry-type genes from Bacillus thuringiensis strains

Genome profiling of an indigenous Bacillus thuringiensis isolate, T405 toxic against the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

In this study, we present the molecular and insecticidal characteristics of an indigenous Bt isolate T405 toxic against the maize fall armyworm (FAW), Spodoptera frugiperda. The presence of cry1, cry2 (cry2Aa & cry2Ab) and vip3A1 genes in T405 was confirmed. The SDS-PAGE gel analysis confirmed the occurrence of Cry and Vip proteins with molecular masses of 130, ∼88 and 65 kDa in T405. LC₅₀ estimates of T405 and HD1 were 161.37 and 910.73 μg ml^-1 for neonates whereas, 412.29 and 1014.95 μg ml^-1 correspondingly for 2^nd instar FAW larvae. Scanning Electron Microscopy depicted the existence of bipyramidal, spherical and cubic crystals in T405 spore suspension. The whole genome sequencing and assembly of T405 produced a total of 563 scaffolds with a genome size of 6,673,691 bp. The BLAST similarity search showed that 12 plasmids were distributed in this genome. Genome annotation revealed the presence of 6174 protein coding genes, 13 rRNA and 98 tRNA, in which 6126 genes were completely annotated for their functions through sequence similarity search, domains/motifs identification and gene ontology studies. Further analysis of these genes identified the presence of many insecticidal toxin protein coding genes viz., cry1Ac32, cry1Ab9, cry1Aa6, cry1Ac5, cry1Aa18, cry1Ab8, cry1Ab11, cry2Aa9, cry1Ia40, cry2Aa9, cry1Ia40, cry2Ab35, cyt, vip3Aa7 and tpp80Aa and several additional virulence assisted factors viz., immune inhibitor A, phospholipase C, sphingomyelinase, cell wall hydrolases, chitinase, hemolysin XhlA and seven urease subunit coding genes (ureA, ureB, ureC, ureD, ureE, ureF, ureG) in the annotated genome.

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.

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.

Molecular characterization of a Bacillus thuringiensis strain from Argentina, toxic against Lepidoptera and Coleoptera, based on its whole-genome and Cry protein analysis

The insecticidal proteins of Bacillus thuringiensis are used in formulations of spore-crystal complexes and their genes have been incorporated into several crops, providing a model for genetic engineering in agriculture. Despite the variability of the Cry proteins described so far, it is still necessary to look for toxins with a broad spectrum of action, since a significant number of pests are not controlled with the available Cry proteins. It is also important to provide alternatives to address the problem of insect resistance, which has already appeared with the use of formulations and with transgenic plants that express cry genes that code for insecticidal proteins. The FCC 7 strain was characterized by the ultrastructural parasporal body under optical and electronic microscopy, and for the detection of Cry8-type proteins by genomic and proteomic approaches. The identity of the strain and the presence of putative toxin encoding genes, and virulence factors analyzed by Illumina Miseq 1500 platform genomic sequencing, was confirmed. The identity of the two Cry8 proteins that make up the parasporal body was confirmed by MALDI-TOF/TOF. To expand knowledge about the insecticidal activity of this strain, we conducted preliminary tests against the cotton boll weevil, Anthonomus grandis. Here we report the characterization of a novel B. thuringiensis isolate native to Argentina (FCC 7) toxic against A. grandis. The strain shows a rounded parasporal body harboring mainly a protein of about 140 kDa and two different types of Cry8 proteins. Through whole-genome sequencing, we identified the presence of two cry8-like crystal protein genes, one vpa-like and two vpb-like genes, and multiple virulence factors, deepening the knowledge of a strain that had already been described as toxic against some lepidopterans and coleopterans, including Spodoptera frugiperda, Anticarsia gemmatalis, Tenebrio molitor and Diabrotica speciosa.

Immunodetection of the toxic portion of Vip3A reveals differential temporal regulation of its secretion among Bacillus thuringiensis strains

AIMS

To devise a protocol for heterologous expression and purification of a partial toxic portion of the Bacillus thuringiensis (Bt) vegetative insecticidal protein Vip3A and using it as an antigen for anti-Vip3A polyclonal antibody development. Also, to evaluate the regulation of Vip3A secretion into culture supernatants (SNs) of different Bt strains based on this antibody.

METHODS AND RESULTS

A primer pair was designed to amplify partially the toxic portion of the vip3A gene from the HD125 strain. The amplicon was cloned in expressing vector to produce a ~35 kDa peptide, which was HPLC-purified prior to rabbit immunizations. The serum containing the polyclonal anti-Vip3A antibody demonstrated a detection sensitivity of 0·4 ng mm^-2 for the antigen in slot-blot experiments. Seven Bt strains from different origins were assessed regarding their temporal secretion of Vip3A toxin. ELISA results showed a strain-specific temporal regulation of Vip3A secretion in culture for the temperate isolates, with no detection of the toxin for the tropical strains, even when the presence of the gene was confirmed by PCR and sequencing.

CONCLUSIONS

Conformational variation in the toxic portion of Vip3A may explain lack of its detection in the tropical strains. Isolates from the same subspecies display physiological variability in proteins' secretion into culture SNs, which can affect screening procedures for more effective strains/toxins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Immunoassays based on the developed anti-Vip3A antibody can be useful in a variety of basic studies. This method can be also coupled with toxicity assays on target insects, for more efficient screening methods of novel Bt strains/toxins with biocontrol applicability.

Molecular characterization and PCR-based screening of cry genes from Bacillus thuringiensis strains

Novel cry genes are potential candidates for resistance management strategies, due to their different structures and modes of action. Therefore, it is desirable to clone and express novel cry genes from several new isolates of Bacillus thuringiensis (Bt). In the present study, 28 Bt strains were characterized at morphological and molecular level. All these strains are Gram positive, endospore forming and had shown different crystal morphologies when viewed under the microscope. The ARDRA (16S rDNA PCR-RFLP technique) with AluI, HaeIII, HinfI and TaqI produced unique and distinguishable restriction patterns used for the molecular characterization of these isolates. Based on UPGMA clustering analysis, Bt strains showed significant molecular diversity and the dendrogram obtained differentiated 28 Bt strains into 1 major cluster at a similarity coefficient 0.56. PCR analysis demonstrated that the Bt strains showed diverse cry gene profiles with several genes per strain. The Bt strain G3C1 showed the presence of maximum cry-type genes by PCR. The toxicological characterization of these cry genes will have huge importance in transgenic technology and will be useful in transgenesis of crop plants for better resistance management.

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.

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.

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.

Cloning, characterization and diversity of insecticidal crystal protein genes of bacillus thuringiensis native isolates from soils of Andaman and Nicobar Islands

Bt strains were isolated from soils of Andaman and Nicobar Islands and characterized by microscopic and molecular methods. Diversity was observed both in protein and cry gene profiles, where majority of the isolates showed presence of 65 kDa protein band on SDS-PAGE while rest of them showed 130, 72, 44, and 29 kDa bands. PCR analysis revealed predominance of cry1I and cry7, 8 genes in these isolates. The PCR screening strategy presented here led us to identify putative novel cry genes which could be active against Coleoptera insects. Variation in the nucleotide sequences of cry genes from the isolates suggests that the genetic diversity of Bt isolates results from the influence of different ecological factors and spatial separation between strains generated by the conquest of different habitats in the soils of Andaman and Nicobar islands. The implications of our studies are important from the point of view of identifying novel cry genes that could be toxic to insects other than lepidoptera.

Development and validation of real-time PCR screening methods for detection of cry1A.105 and cry2Ab2 genes in genetically modified organisms

Primers and probes were developed for the element-specific detection of cry1A.105 and cry2Ab2 genes, based on their DNA sequence as present in GM maize MON89034. Cry genes are present in many genetically modified (GM) plants and they are important targets for developing GMO element-specific detection methods. Element-specific methods can be of use to screen for the presence of GMOs in food and feed supply chains. Moreover, a combination of GMO elements may indicate the potential presence of unapproved GMOs (UGMs). Primer-probe combinations were evaluated in terms of specificity, efficiency and limit of detection. Except for specificity, the complete experiment was performed in 9 PCR runs, on 9 different days and by testing 8 DNA concentrations. The results showed a high specificity and efficiency for cry1A.105 and cry2Ab2 detection. The limit of detection was between 0.05 and 0.01 ng DNA per PCR reaction for both assays. These data confirm the applicability of these new primer-probe combinations for element detection that can contribute to the screening for GM and UGM crops in food and feed samples.

Novel Bacillus thuringiensis δ-endotoxin active against Locusta migratoria manilensis

A novel δ-endotoxin gene was cloned from a Bacillus thuringiensis strain with activity against Locusta migratoria manilensis by PCR-based genome walking. The sequence of the cry gene was 3,432 bp long, and it encoded a Cry protein of 1,144 amino acid residues with a molecular mass of 129,196.5 kDa, which exhibited 62% homology with Cry7Ba1 in the amino acid sequence. The δ-endotoxin with five conserved sequence blocks in the amino-terminal region was designated Cry7Ca1 (GenBank accession no. EF486523). Protein structure analysis suggested that the activated toxin of Cry7Ca1 has three domains: 227 residues forming 7 α-helices (domain I); 213 residues forming three antiparallel β-sheets (domain II); and 134 residues forming a β-sandwich (domain III). The three domains, respectively, exhibited 47, 44, and 34% sequence identity with corresponding domains of known Cry toxins. SDS-PAGE and Western blot analysis showed that Cry7Ca1, encoded by the full-length open reading frame of the cry gene, the activated toxin 1, which included three domains but without the N-terminal 54 amino acid residues and the C terminus, and the activated toxin 2, which included three domains and N-terminal 54 amino acid residues but without the C terminus, could be expressed in Escherichia coli. Bioassay results indicated that the expressed proteins of Cry7Ca1 and the activated toxins (toxins 1 and 2) showed significant activity against 2nd instar locusts, and after 7 days of infection, the estimated 50% lethal concentrations (LC₅₀s) were 8.98 μg/ml for the expressed Cry7Ca1, 0.87 μg/ml for the activated toxin 1, and 4.43 μg/ml for the activated toxin 2. The δ-endotoxin also induced histopathological changes in midgut epithelial cells of adult L. migratoria manilensis.

Genetic diversity of cry gene sequences of Bacillus thuringiensis strains analyzed by denaturing gradient gel electrophoresis

PCR has been widely used to identify cry-type genes, to determine their distribution, to detect new such genes and to predict insecticidal activities. We describe here a molecular approach to analyze the genetic diversity of B. thuringiensis cry-like genes based on denaturing gradient gel electrophoresis (DGGE). This analysis demonstrated that different B. thuringiensis isolates can be distinguished according to its PCR-DGGE profile of cry-like genes. Identification of the resolvable DNA fragments was easy to accomplish by DNA sequencing, which was confirmed in this work. Importantly, the strategy allowed the identification of unknown B. thuringiensis cry-like sequences present in a single strain that remained cryptic after PCR analysis using degenerate primers. The method developed in this work contributes to the availability of molecular techniques for both B. thuringiensis strains and cry-like genes identification and discovery.

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.

Cry-Bt identifier: a biological database for PCR detection of Cry genes present in transgenic plants

We describe the development of a user friendly tool that would assist in the retrieval of information relating to Cry genes in transgenic crops. The tool also helps in detection of transformed Cry genes from Bacillus thuringiensis present in transgenic plants by providing suitable designed primers for PCR identification of these genes. The tool designed based on relational database model enables easy retrieval of information from the database with simple user queries. The tool also enables users to access related information about Cry genes present in various databases by interacting with different sources (nucleotide sequences, protein sequence, sequence comparison tools, published literature, conserved domains, evolutionary and structural data).

AVAILABILITY

http://insilicogenomics.in/Cry-btIdentifier/welcome.html.

New strategy for isolating novel nematicidal crystal protein genes from Bacillus thuringiensis strain YBT-1518

We have developed a strategy for isolating cry genes from Bacillus thuringiensis. The key steps are the construction of a DNA library in an acrystalliferous B. thuringiensis host strain and screening for the formation of crystal through optical microscopy observation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses. By this method, three cry genes--cry55Aa1, cry6Aa2, and cry5Ba2--were cloned from rice-shaped crystals, producing B. thuringiensis YBT-1518, which consists of 54- and 45-kDa crystal proteins. cry55Aa1 encoded a 45-kDa protein, cry6Aa2 encoded a 54-kDa protein, and cry5Ba2 remained cryptic in strain YBT-1518, as shown by SDS-PAGE or microscopic observation. Proteins encoded by these three genes are all toxic to the root knot nematode Meloidogyne hapla. The two genes cry55Aa1 and cry6Aa2 were found to be located on a plasmid with a rather small size of 17.7 kb, designated pBMB0228.

Specific activity of a Bacillus thuringiensis strain against Locusta migratoria manilensis

Bacillus thuringiensis (Bt) has played an important role in biocontrol of pests. However, insecticidal activity of B. thuringiensis against locusts has been rarely reported. Bt strain BTH-13 exhibiting specific activity to locusts was isolated from a soil sample in China and characterized. Its bipyramidal parasporal crystal is mainly composed of a protein of 129kDa, and produces a mature toxin of 64kDa after activation. The pattern of total DNA from BTH-13 showed a large and three small plasmid bands. Known delta-endotoxin genes, cry1Aa, cry1Ab, cry1Ac, cry1C, cry3, cry4 and cry7Aa were not found from strain BTH-13 by PCR amplification. The sequence analysis of a DNA fragment produced by PCR amplification with degenerate cry-selective primers revealed that the fragment encoded a delta-endotoxin segment, which exhibited some similarity to several Cry proteins (41% of the highest similarity to Cry7Ba1). Toxicity tests were performed against Locusta migratoria manilensis, and the results demonstrated that trypsin-treated sporulated cultures and crystal proteins had high toxicity to larval and adult locusts. Cry toxin of BTH-13 was detected on the midguts of treated locusts using immunofluorescent technology, which confirmed the site of action of the crystal proteins in their toxicity for locusts.

Distribution and diversity of Dipteran-specific cry and cyt genes in native Bacillus thuringiensis strains obtained from different ecosystems of Iran

One hundred and twenty-eight Bacillus thuringiensis isolates from fields of different ecological regions of Iran were collected to study the distribution and diversity of Dipteran-specific cry and cyt genes. The percentage of samples with Bt showed significant differences between different regions and also between different fields. The most Bt frequency was observed in the soil samples collected from Caspianic zone (7%) and soils of cotton (17%). Characterization of isolates was based on morphological characteristics of crystals, plasmid profiles and protein band patterns as well as PCR analysis using general and specific primers for 22 different cry and cyt genes encoding proteins active against mosquitoes. Thirty-eight different cry gene profiles were detected in this collection. Several of them were found to be different from all previously published profiles and none of the previous researches reported these numbers of profiles. Strains containing cry2-type genes were the most abundant and represent 57.1% of the isolates. Strains harboring cry24 and cry10 genes were also highly abundant (38.7 and 32.8%, respectively). cry11, cry4, cry17, cry19, cry21, cry29, cyt1, and cry9 genes were less abundant, found in 25.7, 14.3, 11.4, 1.4, 4.3, 1.4, and 10% of the strains, respectively. Among the cry2 gene containing isolates, 37.5% strains harbored cry2Aa, 55% cry2Ab, 2.5% cry2Ac, and 5% other or novel cry2-type genes. Among the cry4 gene containing isolates, 0% strains harbored cry4A, 60% cry4B, and 40% cry4C, cry4D or novel cry4 type genes. Finally, based on crystal morphology, protein patterns and PCR, 21 strains were selected as potentially high Dipteran-active for bioassays. Also our results showed that some of the isolates may harbor minimum a putative novel cry gene.

Cloning and characterization of a novel crystal protein from a native Bacillus thuringiensis isolate highly active against Aedes aegypti

We characterized a novel Bacillus thuringiensis isolate native to Argentina (FCC 41) that exhibits a mosquitocidal activity higher than the reference B. thuringiensis subsp. israelensis. This isolate shows a rounded crystal harboring two major proteins of about 70-80 kDa. Moreover, we cloned and sequenced the encoding gene of one of the crystal proteins (Cry) consisting of an open reading frame of 2061 pb that encodes a protein of 687 amino acid residues. The deduced amino acid sequence has a predicted relative molecular mass of 78 kDa and is 52% and 45% identical to those of the reported Cry24Aa and Cry24Ba sequences, respectively. The novel Cry protein was designated as Cry24Ca, which also exhibited larvicidal activity against Aedes aegypti when its encoding gene was expressed in an Escherichia coli host strain.

Characterization of the highly variable cry gene regions of Bacillus thuringiensis strain ly4a3 by PCR-SSCP profiling and sequencing

Characterization of cry gene contents can help to predict the insecticidal activities of Bacillus thuringiensis isolates and in the searching of new cry genes. PCR-Single-strand conformation polymorphism (SSCP) profiling and sequencing of the highly variable cry gene regions were used to characterize cry gene content of B. thuringiensis strain ly4a3. The highly variable regions with about 1100 bp in sizes were amplified using a degenerate primer pair for cry genes, OL2(d) and OL5(r). A library of the PCR product was constructed, and all white colonies were subjected to PCR using another degenerate primer pair for cry genes, OL3(d) and OL5(r), with products about 250 bp in sizes. Two different profiles were observed based on SSCP profiling for the PCR products. The cry genes in the two corresponding colonies were sequenced and their deduced amino acids showed high identities to Cry1Ab (84.5% approximately 98.4%) and Cry1I (88.78% approximately 98.4%), respectively. This method allows the quick characterization of cry gene content of B. thuringiensis isolates and the detection of new cry genes.