Multiplex PCR screening to detect cry9 genes in Bacillus thuringiensis strains

Involvement of the Bacillus SecYEG Pathway in Biosurfactant Production and Biofilm Formation

With Bacillus species, about 30% of extracellular proteins are translocated through the cytoplasmic membrane, coordinated by the Sec translocase. This system mainly consists of the cytoplasmic ATPase SecA and the membrane-embedded SecYEG channel. The purpose of this work was to investigate the effects of the SecYEG export system on the production of industrial biomolecules, such as biosurfactants, proteases, amylases, and cellulases. Fifty-two isolates of Bacillus species were obtained from traditional fermented foods and then characterized using molecular microbiology methods. The isolates secreted exoenzymes that included cellulases, amylases, and proteases. We present evidence that a biosurfactant-like molecule requires the SecA ATPase and the SecYEG membrane channel for its secretion. In addition, we showed that biomolecules involved in biofilm formation required the SecYEG pathway. This work presents a novel seven-target fragment multiplex PCR assay capable of identification at the species level of Bacillus through a unique SecDF chromosomal gene. The bacterial membrane protein SecDF allowed the discrimination of Bacillus subtilis, B. licheniformis, B. amyloliquefaciens, and B. sonorensis. SecA was able to interact with AprE, AmyE, and TasA. The Rose Bengal inhibitor of SecA crucially affected the interaction of AprE, AmyE, TapA, and TasA with recombinant Gst-SecA. The Rose Bengal prevented Bacillus species from secreting and producing proteases, cellulases, amylases, and biosurfactant-like molecules. It also inhibited the formation of biofilm cell communities. The data support, for the first time, that the SecYEG translocon mediates the secretion of a biosurfactant-like molecule.

Relative activity of 15 bacterial strains against the larvae of Helicoverpa armigera, Spodoptera exigua, and Spodoptera litura (Lepidoptera: Noctuidae)

Crystal toxins produced by different strains of entomopathogenic Bacillus thuringiensis (Bt) have been characterized and widely applied as commercial biological pesticides owing to their excellent insecticidal properties. This study aimed to identify novel bacterial strains effective in controlling Spodoptera exigua Hübner, Helicoverpa armigera Hübner, and Spodoptera litura Fabricius. Fifteen culturable bacterial strains were isolated from 60 dead larvae (H. armigera and S. exigua) collected in the field. The biochemical characteristics and 16S rRNA sequences of these strains indicated that one strain (B7) was Lysinibacillus sp., 12 strains (B1, B3, B4, B5, B6, B8, P2, P3, P4, P5, P6, and DW) were Bt kurstaki, and P2-2 and B2 were Bacillus velezensis subsp. Laboratory bioassays indicated that strains B3, P6, B6, and P4 showed high toxicity to second-instar larvae of S. exigua, with LC50 values of 5.11, 6.74, 205.82, and 595.93 µg/ml, respectively; while the strains P5, B5, B6, and P6, were the most efficient against second-instar larvae of H. armigera with LC50 values of 725.82, 11,022.72, 1,282.90, 2,005.28, respectively, and strains DW, P3, P2, and B4 had high insecticidal activity against second-instar larvae of S. litura with LC50 values of 576.69, 1,660.96, 6,309.42, and 5,486.10 µg/ml, respectively. In conclusion, several Bt kurstaki strains with good toxicity potential were isolated and identified in this study. These strains are expected to be useful for biointensive integrated pest management programs to reduce the use of synthetic insecticides.

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.

A novel Bacillus thuringiensis isolate toxic to cotton pink bollworm (Pectinophora gossypiella Saunders)

In this study, we report a novel indigenous Bacillus thuringiensis (Bt) isolate, T26, which showed spores and crystals under scanning electron microscope and pathogenicity against the pink bollworm (Pectinophora gossypiella Saunders) in artificial diet based bioassay. SDS-PAGE analysis of the spore-crystal mixture of the Bt isolate, T26 revealed presence of three major protein bands of approximate molecular weights of 80, 55 and 40 kDa. The draft genome assembly consists of 56 scaffolds with an entire draft genome size of 5,054,095 bp. NCBI blast analysis revealed that assembled draft genome is spread over in a chromosome (4,818,543 bp) and one plasmid (235,552 bp). NCBI Prokaryotic Genome Annotation Pipeline (PGAP) showed presence of 5033 coding gene sequences and 159 RNAs genes. None of the known lepidopteran active genes (cry1, cry2 and cry9) could be detected with PCR or with whole genome sequence analysis using Bt toxin scanner tool or CryProcessor tool. Thus, presence of protein crystals and toxicity towards cotton pink bollworm and absence of any known cry/vip/cyt type of genes in draft genome indicates it is a novel type of Bt isolate. Further investigation of this genome sequence along with protein sequencing will lead to understand the novel factors responsible for its virulence and could be a useful tool for the insect resistance management in pink bollworm.

Identification of a native Bacillus thuringiensis strain from Sri Lanka active against Dipel-resistant Plutella xylostella

Background

Biopesticides based on strains of the bacterium Bacillus thuringiensis (Bt) are used globally for effective and environmentally friendly pest control. The most serious threat to the sustainable use of these microbial pesticides is the development of resistance on targeted pests. Populations of Plutella xylostella (diamondback moth) have evolved field resistance to Bt pesticides at diverse locations worldwide. Discovery of novel Bt strains with varied toxin profiles that overcome resistance is one of the strategies to increase sustainability of Bt pesticides against P. xylostella. In this study, we report isolation and characterization of a Bt strain named AB1 from Sri Lanka displaying toxicity towards larvae of P. xylostella resistant to the commercial Bt pesticide Dipel.

Methods

Strains of Bt from diverse environments in Sri Lanka were evaluated for protein crystal production through Differential Interference Contrast (DIC) microscopic examination, and for insecticidal activity against P. xylostella in bioassays. The genome of the AB1 strain was sequenced by Hiseq Illumina sequencing to identify the insecticidal genes present in the genome and nano liquid chromatography followed by tandem mass spectrometry (nanoLC/MS/MS) of purified crystal proteins of AB1 was performed to identify the expressed insecticidal proteins. Multilocus sequence typing and Gyrase B gene sequence analyses were performed to identify the phylogenetic origin of the AB1 strain.

Results

The AB1 strain was identified as producing high levels of bipyramidal crystals and displaying insecticidal activity against susceptible and Dipel-resistant strains of P. xylostella. Multilocus sequence typing and phylogenetic analysis of the Gyrase B gene identified that AB1 belongs to the B. thuringiensis subsp. aizawai serotype. Comparative analysis of genomic and proteomic data showed that among the insecticidal protein coding genes annotated from the AB1 genome (cry1Aa, cry1Ca, cry1Da, cry1Ia, cry2Ab and cry9), Cry1Ca and Cry1Da toxins represented most of the toxin fraction in parasporal crystals from AB1. Overall findings warrant further development of B. thuringiensis subsp. aizawai AB1 strain as a pesticide to control P. xylostella.

Diversity of Bacillus thuringiensis isolates from Egyptian soils as shown by molecular characterization

Different techniques were adopted for molecular characterization of several indigenous strains of Bacillus thuringiensis (Bt) previously isolated from Egyptian soil samples. These isolates show different toxicity levels against neonate larvae of both insect species; Spodoptera littoralis (Biosduval); and Helicoverpa armigera (Hübner). The parasporal crystals among the most potent isolates contained polypeptides of about 127 and 130 kDa. PCR screening for genes encoding different Cry genes was performed. The Cry 1 gene is the most abundant in these isolates (83.33%) among tested Cry-type genes, followed by Cry 1 gene subfamilies (Cry 1B and Cry 1C) with percentage of 38.88% and 77.77%, respectively. The tested isolates showed the presence of Cry 2A(a,b) gene, but not all of these isolates were positive for Cry 2 gene (55.55%). Only 27.77% and 16.66% of the tested isolates harbor Cry 4 and Cry 3 genes, respectively. All strains were negative in PCR assays for the Vip 3Aa1 gene. Moreover, DNA fingerprinting using RAPD-PCR was performed to detect the genetic similarities and dissimilarities among the different isolates and standard strains. Assessment of Bt diversity based on the combined analysis of their protein and RAPD-PCR banding patterns was performed. This study demonstrates that Bt strains isolated from Egyptian soil samples can be distinguished and identified on the basis of the distribution of Cry-type genes and RAPD fingerprints.

The correlation of the presence and expression levels of cry genes with the insecticidal activities against Plutella xylostella for Bacillus thuringiensis strains

The use of Bacillusthuringiensis (Bt) strains with high insecticidal activity is essential for the preparation of bioinsecticide. In this study, for 60 Bt strains isolated in Taiwan, their genotypes and the correlation of some cry genes as well as the expression levels of cry1 genes, with their insecticidal activities against Plutella xylostella, were investigated. Pulsed field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) results revealed that the genotypes of these Bt strains are highly diversified. Also, a considerable number of the Bt strains isolated in Taiwan were found to have high insecticidal activities. Since strains that showed individual combined patterns of PFGE and RAPD exhibited distinct insecticidal activities against P. xylostella, thus, these genotypes may be useful for the identification of the new Bt strains and those which have been used in bioinsecticides. In addition, although the presence of cry2Aa1 may have a greater effect on the insecticidal activity of Bt strains in bioassay than other cry genes, only high expression level of cry1 genes plays a key role to determine the insecticidal activity of Bt strains. In conclusion, both RAPD and PFGE are effective in the differentiation of Bt strains. The presence of cry2Aa1 and, especially, the expression level of cry1 genes are useful for the prediction of the insecticidal activities of Bt strains against P. xylostella.

Eco-genetic structure of Bacillus cereus sensu lato populations from different environments in northeastern Poland

The Bacillus cereus group, which includes entomopathogens and etiologic agents of foodborne illness or anthrax, persists in various environments. The basis of their ecological diversification remains largely undescribed. Here we present the genetic structure and phylogeny of 273 soil B. cereus s.l. isolates from diverse habitats in northeastern Poland, with samplings acquired from the last European natural forest (Białowieża National Park), the largest marshes in Europe (Biebrza National Park), and a farm. In multi-locus sequence typing (MLST), despite negative selection in seven housekeeping loci, the isolates exhibited high genetic diversity (325 alleles), mostly resulting from mutation events, and represented 148 sequencing types (131 STs new and 17 STs already described) grouped into 19 complexes corresponding with bacterial clones, and 80 singletons. Phylogenetic analyses showed that 74% of the isolates clustered with B. cereus s.l. environmental references (clade III), while only 11 and 15%, respectively, grouped with isolates of clinical origin (clade I), and B. cereus ATCC 14579 and reference B. thuringiensis (clade II). Predominantly within clade III, we found lineages adapted to low temperature (thermal ecotypes), while putative toxigenic isolates (cytK-positive) were scattered in all clades of the marsh and farm samplings. The occurrence of 92% of STs in bacilli originating from one habitat, and the description of new STs for 78% of the isolates, strongly indicate the existence of specific genotypes within the natural B. cereus s.l. populations. In contrast to the human-associated B. cereus s.l. that exhibit a significant level of similarity, the environmental isolates appear more complex. Thus we propose dividing B. cereus s.l. into two groups, the first including environmental isolates, and the second covering those that are of clinical relevance.

An improved PCR-restriction fragment length polymorphism (RFLP) method for the identification of cry1-type genes

The cry1-type genes of Bacillus thuringiensis represent the largest cry gene family, which contains 50 distinct holotypes. It is becoming more and more difficult to identify cry1-type genes using current methods because of the increasing number of cry1-type genes. In the present study, an improved PCR-restriction fragment length polymorphism (PCR-RFLP) method which can distinguish 41 holotypes of cry1-type genes was developed. This improved method was used to identify cry1-type genes in 20 B. thuringiensis strains that are toxic to lepidoptera. The results showed that the improved method can efficiently identify single and clustered cry1-type genes and can be used to evaluate cry1-type genes in novel strain collections of B. thuringiensis. Among the detected cry1-type genes, we identified four novel genes, cry1Ai, cry1Bb, cry1Ja, and cry1La. The bioassay results from the expressed products of the four novel cry genes showed that Cry1Ai2, Cry1Bb2, and Cry1Ja2 were highly toxic against Plutella xylostella, whereas Cry1La2 exhibited no activity. Moreover, Cry1Ai2 had good lethal activity against Ostrinia furnacalis, Hyphantria cunea, Chilo suppressalis, and Bombyx mori larvae and considerable weight loss activity against Helicoverpa armigera.

Insecticidal activity of Bacillus thuringiensis strains isolated from soil and water

We attempted to search novel Bacillus thuringiensis strains that produce crystals with potential utility in plant protection and with higher activity than strains already used in biopesticide production. Seven B. thuringiensis soil and water isolates were used in the research. We predicted the toxicity of their crystals by cry gene identification employing PCR method. The isolate MPU B63 with interesting, according to us, genes content was used in evaluating its crystal toxicity against Cydia pomonella caterpillars. The strain MPU B63 was cultured from water sample and had cry1Ab, cry1B, and cry15 genes. The LC₅₀ crystals of MPU B63 were compared to LC₅₀ of commercial bioinsecticide Foray determined against C. pomonella (codling moth). The activity of MPU B63 inclusions against codling moth larvae was approximately 24-fold higher than that of Foray. The results are a promising introduction for further study evaluating the potential usefulness of isolate MPU B63 crystals in plant protection.

Two new Brazilian isolates of Bacillus thuringiensis toxic to Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Bacillus thuringiensis is a bacterium used for biopesticides production and pest-resistant plants due to the synthesis of protein crystals by cry genes, which are effective in controlling several insect orders such as Lepidoptera. This work aimed at the evaluation and characterisation of two new B. thuringiensis isolates active against A. gemmatalis (Hübner 1818) larvae, which is the soybean major pest. The results showed that Bt117-4 isolate amplified fragments corresponding to cry2 and cry9 genes, and synthesised protein fragments equivalent to 130, 90 and 45 kDa. The Bt3146-4 isolate amplified DNA fragments corresponding to cry9 gene and synthesised protein fragments of 70, 58 and 38 kDa. Transmission electron microscopy revealed the presence of protein crystals in both isolates. CL50 with Cry purified proteins from Bt117-4 and Bt3146-4, corresponded to 0.195 and 0.191 µg larvae-1, respectively. The two B. thuringiensis isolates selected in this study were effective to control velvetbean caterpillar at laboratory conditions. Field tests should be carried on to develop new biopesticides formulation as well for cry genes resource for Anticarsia gemmatalis resistant transgenic plants.

Screening, diversity and partial sequence comparison of vegetative insecticidal protein (vip3A) genes in the local isolates of Bacillus thuringiensis Berliner

Characterization, direct sequencing of the PCR amplicon and phylogenetic relationship was done to discover a novel Vip protein genes of the Bt isolates, to improve the prospects for insect control, more Vip proteins should be sought out and researched to predict their insecticidal activity. Characterization was based on direct sequencing of PCR amplicon using primers specific to vip3A gene was presented here. 12 out of 18 isolates screened were positive for vip gene-specific primers. Homology search for the partial sequences using BLAST showed that 11 isolates had high similarity to vip3Aa gene and only one fragment with vip3Ae gene (25-100% at nucleotide and amino acid level). Phylogenetic analysis showed that the gene sequences were responsible for geographic separation for divergence within vip genes, consistent with the evaluation of distinct bacterial population. Despite the geographical distances, strains harbouring vip genes have originated from common ancestors may significantly contribute to control resistant insect pests. Some strains have evolved to be quite distinct and others remain as members of closely related groups. The reported method is a powerful tool to find novel Vip3A proteins from large-scale Bt strains which is effective in terms of time and cost. Further the Vip proteins produced by different strains of B. thuringiensis are unique in terms of the sequence divergence and hence may also differ in their insecticidal activities.

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.

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.

PCR-based method for the detection of cry genes in local isolates of Bacillus thuringiensis from Thailand

A total of 134 isolates of Bacillus thuringiensis obtained from different geographical and ecological origins in Thailand were analyzed to determine the distribution and diversity of cry1, cry2 and cry9 genes encoding for Cry proteins toxic to lepidopteran insects. Strains containing cry1-type genes (109/134 or 81.3%) were found at the same frequency as strains harboring cry2 gene (108/134 or 80.6%) whereas only 50 strains contained cry9 gene (50/134 or 37.3%). Seventeen percent (23/134) of the B. thuringiensis isolates did not harbor any cry1, cry2 or cry9 genes. Among cry1 containing isolates, cry1A (49.3%), cry1B (50.0%), cry1G (48.5%), cry1I (49.3%), cry1J (35.1%) and cry1L (47.0%) were considered abundant. The cry2 gene was distributed with high frequency (>70%) in every region of the country. The study of cry gene combinations revealed 14 cry gene profiles.

Screening of cry gene contents of Bacillus thuringiensis strains isolated from avocado orchards in Mexico, and their insecticidal activity towards Argyrotaenia sp. (Lepidoptera: Tortricidae) larvae

AIMS

To screen for Bacillus thuringiensis strains from avocado orchards in two Mexican states with lepidopteran-specific cry gene content and evaluate their insecticidal activity against Argyrotaenia sp., an undescribed species present in avocado orchards.

METHODS AND RESULTS

Lepidopteran-active cry1, cry2 and cry9 genes were detected by PCR analysis in 37 isolates. cry1 genes were more frequent in Michoacán, but were undetected in Nayarit isolates. cry9 and cry2 genes were detected in isolates from both states, although cry2 genes were less frequent. A variety of crystal shapes were observed among the isolates. According to gene profile, eight isolates were selected and tested against 2-day old Argyrotaenia sp. larvae. Standard strain HD-125 caused the highest mortality followed by strain MR-26 from Michoacán at a concentration of 500 microg ml(-1), respectively.

CONCLUSIONS

Bacillus thuringiensis strains isolated from avocado orchards exhibit a low toxic activity towards Argyrotaenia sp. larvae, in spite of their specific cry gene content.

SIGNIFICANCE AND IMPACT OF THE STUDY

Toxic activity of B. thuringiensis is not necessarily related to insect pest habitat and neither to specific cry gene content associated to other lepidopterans.

Identification of vip3A-type genes from Bacillus thuringiensis strains and characterization of a novel vip3A-type gene

AIMS

To search for novel Vip3A proteins for controlling insect pests.

METHODS AND RESULTS

A pair of universal primers was designed based on the conserved regions of five vip3A genes. Amplified products were digested with the HindIII and EcoR enzymes so as to confirm different restriction fragment length polymorphism (RFLP) patterns used to identify vip3A-type genes. The vip3A gene types of 606 Bacillus thuringiensis strains were screened and three patterns of RFLP were successfully identified. Two novel vip3A genes were found and one of these, vip3Aa19, was further characterized and its product was confirmed toxic to Spodoptera exigua, Helicoverpa armigera and Plutella xylostella larvae. Partial sequences of another novel vip3A-type gene were obtained that shared 83% homology with that of the vip3Af1 gene.

CONCLUSIONS

A polymerase chain reaction (PCR)-RFLP system we developed could be used for identifying novel vip3A-genes from B. thuringiensis strains. A novel Vip3A protein was found to have a broader insecticidal spectrum.

SIGNIFICANCE AND IMPACT OF THE STUDY

The reported method is a powerful tool to find novel Vip3A proteins from large-scale B. thuringiensis strains. The novel Vip3A protein may be used to control insect pests or resistant insect pests by constructing genetically engineered strains or transgenic plants.

Diversity of Colombian strains of Bacillus thuringiensis with insecticidal activity against dipteran and lepidopteran insects

AIM

To evaluate the genetic and molecular diversity and insecticidal activity of Bacillus thuringiensis isolates from all the natural regions of Colombia.

METHODS AND RESULTS

A total of 445 isolates from a collection of B. thuringiensis were characterized. The parasporal crystal morphology that was most abundant was bipyramidal (60%). Almost 10% of the isolates were toxic to Spodoptera frugiperda and 5.6% against Culex quinquefasciatus larvae. cry gene content determined by PCR indicated that 10.6% of the isolates contained cry1 genes and 1.1% contained cry2, cry4 or cry11 genes. Protein content of the parasporal crystal was determined by SDS-PAGE; 25 and 18 different protein profiles were found in isolates active against S. frugiperda and C. quinquefasciatus, respectively.

CONCLUSIONS

Bacillus thuringiensis presents great genetic and molecular diversity even in isolates from the same soil sample. Moreover, the diversity and activity of the isolates might have a relationship with the geographical origin of the samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained here indicate that some of the B. thuringiensis isolates characterized in this study are potential control agents that could be used in programmes against mosquitoes and S. frugiperda.

Analysis of cry Gene Profiles in Bacillus Thuringiensis Strains Isolated During Epizootics in Cydia pomonella L

The crystal morphology and the profiles of genes encoding protein toxins (Cry and Cyt) were analyzed in 12 Bacillus thuringiensis strains isolated during epizootics in laboratory culture lines of Cydia pomonella, 2 isolates cultured from Leucoma salicis larvae, and 9 reference strains. Epizootic isolates produced crystals of the same bipyramidal shape; however, they revealed a variety of number and type of cry genes. Genes cry1I, cry2Ab, and cry9B were the most frequently observed in epizootic strains. Gene cry1I was noted in of 50% epizootic isolates. Eighty-three percent of them harbored gene cry2Ab. Gene cry9B was found for 42% of strains isolated during epizootics. Three isolates showed the largest number of cry genes and their variety; hence, they were chosen for the toxicity assay of their crystals and spores on C. pomonella larvae. One of them had approximately sixfold higher insecticidal activity than the reference strain B. thuringiensis subsp. kurstaki BTK STANDARD.

Assessment of cry1 gene contents of Bacillus thuringiensis strains by use of DNA microarrays

A single Bacillus thuringiensis strain can harbor numerous different insecticidal crystal protein (cry) genes from 46 known classes or primary ranks. The cry1 primary rank is the best known and contains the highest number of cry genes which currently totals over 130. We have designed an oligonucleotide-based DNA microarray (cryArray) to test the feasibility of using microarrays to identify the cry gene content of B. thuringiensis strains. Specific 50-mer oligonucleotide probes representing the cry1 primary and tertiary ranks were designed based on multiple cry gene sequence alignments. To minimize false-positive results, a consentaneous approach was adopted in which multiple probes against a specific gene must unanimously produce positive hybridization signals to confirm the presence of a particular gene. In order to validate the cryArray, several well-characterized B. thuringiensis strains including isolates from a Mexican strain collection were tested. With few exceptions, our probes performed in agreement with known or PCR-validated results. In one case, hybridization of primary- but not tertiary-ranked cry1I probes indicated the presence of a novel cry1I gene. Amplification and partial sequencing of the cry1I gene in strains IB360 and IB429 revealed the presence of a cry1Ia gene variant. Since a single microarray hybridization can replace hundreds of individual PCRs, DNA microarrays should become an excellent tool for the fast screening of new B. thuringiensis isolates presenting interesting insecticidal activity.

Construction of a Pseudomonas sp. derivative carrying the cry9Aa gene from Bacillus thuringiensis and a proposal for new standard criteria to assess entomocidal properties of bacteria

An isolate of Pseudomonas sp. (16S rDNA sequence 98% homologous to P. graminis and P. lutea) was isolated from the phyllosphere of black pine in northern Italy and used as a host for the gene encoding the Cry9Aa entomocidal toxin from Bacillus thuringiensis subsp. galleriae. An expression system featuring a synthetic highest-consensus promoter specifically tailored for the regulated induction of cloned genes over a broad range of Gram-negative bacteria was used to drive the production of the introduced toxin. The construct showed effective toxicity toward larvae of the greater wax moth (Galleria mellonella), which was also used as a model insect for establishing a number of newly proposed toxicity indices (LC50 cellular efficiency, toxin cellular efficiency, GMO efficiency, lethal cellular intake). These were devised in order to express toxicities of entomocidal bacteria in a standard fashion enabling the fine tuning of biocontrol treatments as well as the comparative evaluation of different reports.

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

We designed five degenerate primers for detection of novel cry genes from Bacillus thuringiensis strains. An efficient strategy was developed based on a two-step PCR approach with these primers in five pair combinations. In the first step, only one of the primer pairs is used in the PCR, which allows amplification of DNA fragments encoding protein regions that include consensus domains of representative proteins belonging to different Cry groups. A second PCR is performed by using the first-step amplification products as DNA templates and the set of five primer combinations. Cloning and sequencing of the last-step amplicons allow both the identification of known cry genes encoding Cry proteins covering a wide phylogenetic distance and the detection and characterization of cry-related sequences from novel B. thuringiensis isolates.

The clonal structure of Bacillus thuringiensis isolates from north-east Poland does not correlate with their cry gene diversity

The genetic relationship among 103 natural Bacillus thuringiensis isolates was investigated on the basis of polymerase chain reaction amplification of their specific crystal (cry) protein type genes and chromosomal DNA profiling by pulsed-field gel electrophoresis (PFGE). The strains were recovered from the intestines of small wild rodents and insectivores from the Biebrza National Park and the Lomza Landscape Park of the Narew River Valley in north-east Poland. The percentage of B. thuringiensis strains harbouring genes coding for toxins active against Lepidoptera (cry1, cry2, cry9) was very high (64%) compared with that of Diptera-specific strains (cry4, 14%). No strain with cry genes coding for proteins directed against coleopteran larvae and nematodes was found. After digestion with NotI and AscI, only nine PFGE pulsotypes were observed among all isolates, indicating a clonal structure for the B. thuringiensis population from NE Poland. Interestingly, no correlation was observed between the DNA pulsotype strains and their crystal gene content and diversity. These results therefore emphasize the importance of cry gene horizontal transfer occurring among natural isolates of B. thuringiensis.

Identification of cry1I-type genes from Bacillus thuringiensis strains and characterization of a novel cry1I-type gene

A PCR-restriction fragment length polymorphism method for identification of cry1I-type genes from Bacillus thuringiensis was established by designing a pair of universal primers based on the conserved regions of the genes to amplify 1,548-bp cry1I-type gene fragments. Amplification products were digested with the Bsp119I and BanI enzymes, and four kinds of known cry1I-type genes were successfully identified. The results showed that cry1I-type genes appeared in 95 of 115 B. thuringiensis isolates and 7 of 13 standard strains. A novel cry1I-type gene was found in one standard strain and six isolates. The novel cry1I gene was cloned from B. thuringiensis isolate Btc007 and subcloned into vector pET-21b. Then it was overexpressed in Escherichia coli BL21(DE3). The expressed product was shown to be toxic to the diamondback moth (Plutella xylostella), Asian corn borer (Ostrinia furnacalis), and soybean pod borer (Leguminivora glycinivorella). However, it was not toxic to the cotton bollworm (Helicoverpa armigera), beet armyworm (Spodoptera exigua), or elm leaf beetle (Pyrrhalta aenescens) in bioassays. Subsequently, the Cry protein encoded by this novel cry gene was designated Cry1Ie1 by the B. thuringiensis delta-endotoxin nomenclature committee.

Pathogenicity of Bacillus thuringiensis isolated from two species of Acromyrmex (Hymenoptera, Formicidae)

The control of Acromyrmex leaf-cutting ants is necessary due to the severe damage they cause to diverse crops. A possibility was to control them using the bacterium Bacillus thuringiensis (Bt) that characteristically produces insecticidal crystal proteins (ICPs). The ICPs have been effective in controlling lepidopterans, dipterans, and coleopterans, but their action against hymenopterans is unknown. This paper describes an attempt to isolate Bt from ants of two Acromyrmex species, to evaluate its pathogenicity towards these ants, and to test isolates by PCR. Bacterial isolates of Bt obtained from A. crassispinus and A. lundi have been assayed against A. lundi in the laboratory. The bioassays were carried out in BOD at 25 degrees C, with a 12-hour photoperiod, until the seventh day after treatment. The Bt isolates obtained were submitted to total DNA extraction and tested by PCR with primers specific to cry genes. The results showed Bt presence in 40% of the assessed samples. The data from the in vivo assays showed a mortality rate higher than 50% in the target population, with the Bt HA48 isolate causing 100% of corrected mortality. The PCR results of Bt isolates showed a magnification of DNA fragments relative to cry1 genes in 22% of the isolates, and cry9 in 67%. Cry2, cry3, cry7, and cry8 genes were not detected in the tested samples, and 22% had no magnified DNA fragments corresponding to the assessed cry genes. The results are promising not only regarding allele identification in new isolates, but also fort the assays aimed at determining the Bt HA48 LC50's, which can eventually be applied in controlling of Acromyrmex leaf-cutting ants.

Characterization of cry1, cry2, and cry9 genes in Bacillus thuringiensis isolates from China

Bacillus thuringiensis isolates from different ecological regions and sources of China were analyzed to study the distribution and diversity of cry genes and to detect the presence of novel cry genes. Strains containing cry1-type genes were the most abundant and represent 237 of the 310 B. thuringiensis isolates (76.5%). About 70 and 15.5% of the isolates contained a cry2 gene or cry9 gene, respectively, while 10.0% of the strains did not contain a cry1, cry2, or cry9 gene. Among the cry1 containing isolates, cry1A (67.7%), cry1I (60.6%), cry1C (43.9%), and cry1D (39.4%) genes were the most abundant. Forty-three different cry1 gene profiles were detected in this collection. Several cry1 genes were associated at a high frequency, such as the cry1C-cry1D and cry1A-cry1I gene combination. The cry1A and cry2 amplicons were digested with selected restriction enzymes to examine sequence diversity. Based on this RFLP analysis, one novel cry1A-type gene was observed.