Extended screening by PCR for seven cry-group genes from field-collected strains of Bacillus thuringiensis

Screening and characterization of Bacillus thuringiensis isolates for high production of Vip3A and Cry proteins and high thermostability to control Spodoptera spp

Bacillus thuringiensis (Bt) is an entomopathogenic bacterium that produces crystalline (Cry and Cyt) and soluble (vegetative insecticidal proteins or Vips) proteins during the sporulation and vegetative growth phases, respectively. Combining Cry and Vip proteins could delay insect resistance development and exhibit synergistic activity against various insect pests. This study aims to screen Bt isolates collected from Thailand for high Vip3A and Cry protein production levels and high thermostability to control Spodoptera spp. Among the selected Bt isolates with high target protein synthesis, Bt isolate 506 was found to be safe for further biopesticide formulation due to the absence of non-specific metabolite, as determined by the detection of thermo-stable β-exotoxin I based on biological assays and PCR analysis. Bt isolate 506 showed the presence of Cry1A, Cry2A, and Vip3A-type proteins identified as Cry1Aa45, Cry2Aa22, and Vip3A87, respectively. The insecticidal activity of whole culture extracts containing Vip3A and Cry mixtures and culture supernatants containing secreted Vip3A protein was evaluated against the second-instar larvae of S. exigua and S. frugiperda. The Bt isolate 506 showed high toxicity against both insects, and the insecticidal proteins produced by this isolate retained their activity after heating at 50 °C. This Bt isolate is a promising candidate for further development as a biopesticide against lepidopteran pests.

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

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

Abundance, distribution, and expression of nematicidal crystal protein genes in Bacillus thuringiensis strains from diverse habitats

Bacillus thuringiensis (Bt) is a Gram-positive bacterium that accumulates pesticidal proteins (Cry and Cyt) in parasporal crystals. Proteins from the Cry5, App6 (formerly Cry6), Cry12, Cry13, Cry14, Cry21, and Xpp55 (formerly Cry55) families have been identified as toxic to nematodes. In this study, a total of 846 Bt strains belonging to four collections were analyzed to determine the diversity and distribution of the Bt Cry nematicidal protein genes. We analyzed their presence by PCR, and positives were confirmed by sequencing. As a result, 164 Bt isolates (20%) contained at least one gene coding for nematicidal Cry proteins. The cry5 and cry21 genes were enriched in collection 1 and were often found together in the same strain. Differently, in collection 4, obtained from similar habitats but after 10 years, cry14 was the gene most frequently found. In collection 2, cry5 and app6 were the most abundant genes, and collection 3 had a low incidence of any of these genes. The results point to high variability in the frequencies of the studied genes depending on the timing, geographical origins, and sources. The occurrence of cry1A, cry2, and cry3 genes was also analyzed and showed that the nematicidal Cry protein genes were frequently accompanied by cry1A + cry2. The expression of the genes was assessed by mass spectrometry showing that only 14% of the positive strains produced nematicidal proteins. To our knowledge, this is the first comprehensive screening that examines the presence and expression of genes from the seven known Bt Cry nematicidal families.

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.

Molecular cloning of a new cry2A-type gene from Bacillus thuringiensis strain Nn10 and its expression studies

In the present study, eight indigenous Bacillus thuringiensis isolates of Western Ghats of India with more than 90% toxicity against Helicoverpa armigera were characterized for cry2A gene sub families. Seven of the eight isolates harboured cry2Aa, cry2Ab and cry2Ac genes alone and or in combination. Further, the indigenous cry2Aa gene(s) from Bacillus thuringiensis isolate Nn10 which showed 100% mortality against Helicoverpa armigera was cloned and expressed into recombinant Bt strains for management of resistance development in insects. The ORF of cry2Aa (∼1.9 kb) gene(s) from Nn10 isolate was ligated with T/A vector (pTZ57 R/T) and expressed in E. coli, DH5α. Automated sequence analysis of newly cloned recombinant cry2Aa revealed 99% homology to 916 bases in the 3' region of minus strand and 100% homology with 720 bases in the 5' region of holotype cry2Aa1 gene. The partial Cry2Aa amino acid sequence of Bt strain, Nn10, deduced from the nucleotide sequence generated by M13F primer showed four amino acid variation in comparison to Cry2Aa1 holotype, at 338, 345, 346 and 489^th position of ORF and the sequence was submitted to the NCBI. Further the expression of ORF of cry2Aa of Nn10 into acrystalliferous Bt strain, 4Q7 using expression vector pHT3P2T under the transcriptional control of cry3Aa promoter and cry2Aa terminator. SDS PAGE analysis of recombinant protein exhibited a prominent band of about 65 kDa. Bioassay studies revealed that recombinant proteins, Cry2Aa of Nn10 was toxic to Helicoverpa armigera with LC50 value of 7.26 μg ml^-1.

Genotype and virulence gene analyses of Bacillus cereus group clinical isolates from the Chinese softshell turtle (Pelodiscus sinensis) in Taiwan

Chinese softshell turtles (Pelodiscus sinensis) (CST) are susceptible to infections by bacteria belonging to the Bacillus cereus group (Bcg). Bcg includes several closely related species, two of which, B. cereus and B. thuringiensis, are pathogens of aquatic animals or insects. In the present study, we collected 57 Bcg isolates obtained from diseased CST from 2016 to 2019 in Kaohsiung and Pingtung, the areas with the most CST farms in Taiwan. All isolates were divided into four genotypes with two restriction enzymes, SmaI and NotI, by pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR). Representative isolates from each genotype were subjected to phylogenetic tree analysis using 16S rDNA and pyruvate carboxylase genes as phylogenetic markers, and these CST isolates appeared in different clades. PCR was performed targeting six selected virulence genes, four of which were detected in CST isolates, including cytotoxin K (1/57), hblC of the haemolysin BL complex (46/57), nheA of the non-haemolytic enterotoxin complex (52/57) and enterotoxin FM (57/57), whereas cereulide synthetase and cereulide peptide synthase-like genes were not detected in any isolates.

Identification of Bacillus thuringiensis Strains for the Management of Lepidopteran Pests

Bacillus thuringiensis (Bt)-based bioinsecticides and transgenic plants expressing proteins with insecticidal activity (Cry and Vip) have been successfully used in several integrated pest management programs worldwide. Lepidoptera comprise some of the most economically important insect pests of the major agricultural crops. In this study, the toxicity of 150 Bt strains was evaluated against Helicoverpa armigera (Hübner) larvae. Eight strains (426, 520B, 1636, 1641, 1644, 1648, 1657 and 1658) showed high insecticide activity against H. armigera and were therefore tested against Anticarsia gemmatalis (Hübner), Spodoptera cosmioides (Walker), Chrysodeixis includens (Walker), and Diatraea saccharalis (Fabricius) larvae. Our results showed that most of the Bt strains were also toxic to these lepidopteran species. The biochemical and molecular analyses of these strains revealed that they had a similar protein profile; however, their cry and vip gene contents were variable. In addition, the median lethal concentration (LC₅₀) of the selected strains indicated that the strains 1636, 1641, and 1658 were the most effective against H. armigera, showing LC₅₀ values of 185.02, 159.44, and 192.98 ng/cm², respectively. Our results suggest that the selected Bt strains have great potential to control the lepidopteran pests H. armigera, A. gemmatalis, D. saccharalis, S. cosmioides, and C. includes.

Isolation, molecular characterization and pathogenicity of native Bacillus thuringiensis, from Ethiopia, against the tomato leafminer, Tuta absoluta: Detection of a new high lethal phylogenetic group

Tuta absoluta (tomato leafminer) is one of the devastating agricultural pest that attack mainly tomatoes. The continuous use of chemical pesticides is not affordable and poses a collateral damage to human and environmental health. This requires integrated pest management to reduce chemical pesticides. B. thuringiensis is a cosmopolitan, antagonistic soil bacterium used to control agricultural pests. In this study, effective Bt strains were screened from different sample sources based on their lepidopteran specific cry genes and larvicidal efficacy against tomato leafminer, T. absoluta under laboratory conditions. Of the 182 bacterial isolates, 55 (30 %) of isolates harbored parasporal protein crystals. Out of these, 34 (62 %) isolates possess one or more lepidopteran specific cry genes: 20 % of isolates positive for cry2, 18.2 % for cry9, 3.6 % for cry1, 16.4 % for cry2 + cry9, 1.8 % for cry1 + cry9, and 1.8 % for cry1 + cry2 + cry9. However, 21 (38.2 %) isolates did not show any lepidopteran specific cry genes. Isolates positive for cry genes showed 36.7-75 % and 46.7-98.3 % mortality against second and third instar larvae of the T. absoluta at the concentration of 10⁸ colony forming units (CFUs) ml^-1. Cry1 and cry1 plus other cry gene positive isolates were relatively more pathogenic against T. absoluta. However, third instar larvae of the T. absoluta was more susceptible than second instar larvae. Two of the isolates, AAUF6 and AAUMF9 were effective and scored LT₅₀ values of 2.3 and 2.7 days and LC₅₀ values of 3.4 × 10³ and 4.15 × 10³ CFUs ml^-1 against the third instar larvae, respectively. The phylogenetic studies showed some congruence of groups with cry gene profiles and lethality level of isolates and very interestingly, we have detected a putative new phylogenetic group of Bt from Ethiopia.

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.

Antimicrobial resistance, virulence characteristics and genotypes of Bacillus spp. from probiotic products of diverse origins

Spore-forming probiotic Bacillus spp. have received extensively increasing scientific and commercial interest, but raised the concerns in the potential risks and pathogenesis. In this study, 50 commercial probiotic products were collected from all over the country and Bacillus spp. isolated from products were evaluated for the safety on the aspects of hemolytic activity, contamination profiles, toxin genes, cytotoxicity, antimicrobial resistance, and genotyping. 34 probiotic products (68%) exhibited hemolysis, including 19 human probiotics, 9 animal probiotics, and 6 plant probiotics. 28 products (56%) contained other bacteria not labeled in the ingredients. 48 strains in Bacillus spp. including 17 B. subtilis group isolates, 28 B. cereus, and 3 other Bacillus spp. were isolated from human, food animal, and plant probiotic products. Detection rates of enterotoxin genes, nheABC and hblCDA, and cytotoxin cytK2 in 48 Bacillus spp. isolates were 58%, 31%, and 46%, respectively. Also, one isolate B. cereus 34b from an animal probiotic product was positive for ces, encoding cereulide. 28 of 48 Bacillus spp. isolates were cytotoxic. 19 of 28 B. cereus isolates maintained to exhibit hemolysis after heat treatment. All 48 Bacillus spp. isolates exhibited resistance to lincomycin, and 5 were resistant to tetracycline. The genotyping of commercial probiotic Bacillus spp. reported in this study showed that ces existed in B. cereus 34b with the specific sequence type (ST1066). These findings support the hypothesis that probiotic products were frequently contaminated and that some commercial probiotics consisted of Bacillus spp. may possess toxicity and antimicrobial resistance genes. Thus, the further efforts are needed in regarding the surveillance of virulence factors, toxins, and antibiotic resistance determinants in probiotic Bacillus spp.

Enteropathogenic Potential of Bacillus thuringiensis Isolates from Soil, Animals, Food and Biopesticides

Despite its benefits as biological insecticide, Bacillus thuringiensis bears enterotoxins, which can be responsible for a diarrhoeal type of food poisoning. Thus, all 24 isolates from foodstuffs, animals, soil and commercially used biopesticides tested in this study showed the genetic prerequisites necessary to provoke the disease. Moreover, though highly strain-specific, various isolates were able to germinate and also to actively move, which are further requirements for the onset of the disease. Most importantly, all isolates could grow under simulated intestinal conditions and produce significant amounts of enterotoxins. Cytotoxicity assays classified 14 isolates as highly, eight as medium and only two as low toxic. Additionally, growth inhibition by essential oils (EOs) was investigated as preventive measure against putatively enteropathogenic B. thuringiensis. Cinnamon Chinese cassia showed the highest antimicrobial activity, followed by citral, oregano and winter savory. In all tests, high strain-specific variations appeared and must be taken into account when evaluating the hazardous potential of B. thuringiensis and using EOs as antimicrobials. Altogether, the present study shows a non-negligible pathogenic potential of B. thuringiensis, independently from the origin of isolation. Generally, biopesticide strains were indistinguishable from other isolates. Thus, the use of these pesticides might indeed increase the risk for consumers’ health. Until complete information about the safety of the applied strains and formulations is available, consumers or manufacturers might benefit from the antimicrobial activity of EOs to reduce the level of contamination.

Differential side-effects of Bacillus thuringiensis bioinsecticide on non-target Drosophila flies

Bioinsecticides based on Bacillus thuringiensis (Bt) spores and toxins are increasingly popular alternative solutions to control insect pests, with potential impact of their accumulation in the environment on non-target organisms. Here, we tested the effects of chronic exposure to commercial Bt formulations (Bt var. kurstaki and israelensis) on eight non-target Drosophila species present in Bt-treated areas, including D. melanogaster (four strains). Doses up to those recommended for field application (~ 106 Colony Forming Unit (CFU)/g fly medium) did not impact fly development, while no fly emerged at ≥ 1000-fold this dose. Doses between 10- to 100-fold the recommended one increased developmental time and decreased adult emergence rates in a dose-dependent manner, with species-and strain-specific effect amplitudes. Focusing on D. melanogaster, development alterations were due to instar-dependent larval mortality, and the longevity and offspring number of adult flies exposed to bioinsecticide throughout their development were moderately influenced. Our data also suggest a synergy between the formulation compounds (spores, cleaved toxins, additives) might induce the bioinsecticide effects on larval development. Although recommended doses had no impact on non-target Drosophila species, misuse or local environmental accumulation of Bt bioinsecticides could have side-effects on fly populations with potential implications for their associated communities.

Isolates of Bacillus thuringiensis from Maranhão biomes with potential insecticidal action against Aedes aegypti larvae (Diptera, Culicidae)

Entomopathogenic agents are viable and effective options due to their selective action against insects but benign effects on humans and the environment. The most promising entomopathogens include subspecies of Bacillus thuringiensis (Bt), which are widely used for the biological control of insects, including mosquito vectors of human pathogens. The efficacy of B. thuringiensis toxicity has led to the search for new potentially toxic isolates in different regions of the world. Therefore, soil samples from the Amazon, Cerrado and Caatinga biomes of the state of Maranhão were evaluated for their potential larvicidal action against Aedes aegypti. The isolates with high toxicity to mosquito larvae, as detected by bioassays, were subjected to histological evaluation under a light microscope to identify the genes potentially responsible for the toxicity. Additionally, the toxic effects of these isolates on the intestinal epithelium were assessed. In the new B. thuringiensis isolates toxic to A. aegypti larvae, cry and cyt genes were amplified at different frequencies, with cry4, cyt1, cry32, cry10 and cry11 being the most frequent (33-55%) among those investigated. These genes encode specific proteins toxic to dipterans and may explain the severe morphological changes in the intestine of A. aegypti larvae caused by the toxins of the isolates.

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.

Larvicidal and adulticidal effects and ultrastructural changes of larvae midgut epithelium of Musca domestica (Diptera: Muscidae) fed with Bacillus thuringiensis var. kyushuensis

INTRODUCTION

Musca domestica is resistant to many insecticides; hence, biological control is a suitable alternative.

METHODS

We evaluated the lethality of strain Btk176 towards the larval and adult M. domestica and the histopathological effects in the larvae midgut.

RESULTS

We observed 99% larval and 78.9% adult mortality within 48 hours of spore ingestion (dosage, 2.4×108 CFU/ml). The histopathological effects were consistent with cytotoxicity. PCR analysis showed the presence of the cry1Ba gene. Transmission electron microscopy revealed a bipyramidal parasporal body. Thurigiensin activity was not detected.

CONCLUSIONS

The serovar, Btk176 might be a potential biocontrol agent for houseflies.

Differentiation of Bacillus thuringiensis From Bacillus cereus Group Using a Unique Marker Based on Real-Time PCR

The efficiency of a novel biomarker (the transcriptional regulator, XRE) was tested and evaluated in differentiating Bacillus thuringiensis from Bacillus cereus group species in environmental and spiked samples based on PCR and real-time PCR. Totally 120 strains, representing two bacterial groups, B. cereus group and non-Bacillus sp., were used to evaluate the performance of XRE and crystal protein (cry2, an existing biomarker). Further, three diverse samples (kimbap, lettuce, and spinach) were inoculated with B. thuringiensis and prominent biomarkers XRE and cry2 were used as targets. Direct analysis of the detection results for the pure cultures of B. cereus group wild-types, references and type strains revealed an accuracy rate of 97.5% targeting XRE, and 83.3% targeting cry2. The real-time PCR was constructed with a R ²-value of 0.993. For the artificially contaminated samples, a concentration of 10³ CFU/g of B. thuringiensis in spiked food samples could be detected using real-time PCR targeting XRE. A good performance was obtained with XRE in discriminating B. thuringiensis from B. cereus groups, as well as detecting B. thuringiensis in spiked food samples with PCR or real-time PCR. Therefore, this real-time PCR targeting XRE can be used as a dependable and promising tool to identify B. thuringiensis in foods.

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.

Toxin Gene Contents and Activity of Bacillus thuringiensis Strains Against Two Sugarcane Borer Species, Diatraea saccharalis (F.) and D. flavipennella (Box)

Bacillus thuringiensis (Berliner) bears essential characteristics in the control of insect pests, such as its unique mode of action, which confers specificity and selectivity. This study assessed cry gene contents from Bt strains and their entomotoxicity against Diatraea saccharalis (F.) and Diatraea flavipennella (Box) (Lepidoptera: Crambidae). Bioassays with Bt strains were performed against neonates to evaluate their lethal and sublethal activities and were further analyzed by PCR, using primers to identify toxin genes. For D. saccharalis and D. flavipennella, 16 and 18 strains showed over 30% larval mortality in the 7th day, respectively. The LC₅₀ values of strains for D. saccharalis varied from 0.08 × 10⁵ (LIIT-0105) to 4104 × 10⁵ (LIIT-2707) spores + crystals mL^-1. For D. flavipennella, the LC₅₀ values of strains varied from 0.40 × 10⁵ (LIIT-2707) to 542 × 10⁵ (LIIT-2109) spores + crystals mL^-1. For the LIIT-0105 strain, which was the most toxic to D. saccharalis, the genes cry1Aa, cry1Ab, cry1Ac, cry1B, cry1C, cry1D, cry1F, cry1I, cry2Aa, cry2Ab, cry8, and cry9C were detected, whereas for the strain LIIT-2707, which was the most toxic to D. flavipennella, detected genes were cry1Aa, cry1Ab, cry1Ac, cry1B, cry1D, cry1F, cry1I, cry2Aa, cry2Ab, and cry9. The toxicity data and toxin gene content in these strains of Bt suggest a great variability of activity with potential to be used in the development of novel biopesticides or as source of resistance genes that can be expressed in plants to control pests.

Molecular Characterization of the cry Gene profile of Bacillus thuringiensis Isolated from a Caribbean Region of Colombia

In order to characterize native strains of Bacillus thuringiensis of the Colombian Caribbean with toxic effect against insect vectors, 28 samples of bacteria identified as B. thuringiensis were isolated from different soils and muds around the city of Valledupar. Using a biological test, five isolates of B. thuringiensis showed toxic effect against larvae of Aedes aegypti. PCR methods were used to detect cry1, cry2, cry4B, cry10 and cyt1 genes. Cry1 and cry2 genes were detected in 35.7% and 32.1% of the 28 isolates analyzed, respectively. Surprisingly, reduced lengths of cry4B gene segments were detected in 28.6% of B. thuringiensis samples. The presence of cry10 or cyt1 was not detected in any of the 28 samples of B. thuringiensis, despite the high sensitivity of the assays used. The results show that B. thuringiensis samples from the Colombian Caribbean have atypical characteristics compared to those of Latin America and elsewhere in the world, which is consistent with the idea that the geographic origin of B. thuringiensis samples is associated with their biological and genetic characteristics.

Selection and characterization of Bacillus thuringiensis strains from northwestern Himalayas toxic against Helicoverpa armigera

In this study, we present the selection and the characterization of Bacillus thuringiensis (Bt) strains with respect to their cry/cyt gene content and toxicity evaluation toward one of the most important polyphagous lepidopteran pest, Helicoverpa armigera. Fifty-six Bt isolates were obtained from 10 different regions of northwestern Himalayas, recording a total B. thuringiensis index of 0.62. Scanning electron microscopy revealed presence of bipyramidal, spherical, flat and irregular crystal shapes; SDS-PAGE analysis of spore-crystal mixtures showed the prominence of 130, 70, and 100 kDa protein bands in majority of the isolates; PCR analysis with primers for eight cry and cyt gene families and 13 cry gene subfamilies resulted in isolates showing different combinations of insecticidal genes. Strains containing cry1 were the most abundant (57.1%) followed by cyt2 (46.42%), cry11 (37.5%), cry2 (28.57%), cry4 (21.42%), cyt1 (19.64%), cry3 (8.9%), and cry7, 8 (7.14%). A total of 30.35% of the strains did not amplify with any of the primers used in this study. Median lethal concentration 50 (LC50 ) estimates of spore-crystal mixtures of Bt-JK12, 17, 22, 48, and 72 against second instar larvae of H. armigera was observed to be 184.62, 275.39, 256.29, 259.93 μg ml-1 , respectively. B. thuringiensis presents great diversity with respect to the presence of crystal protein encoding genes and insecticidal activity. Four putative toxic isolates identified in this study have potential application in insect pest control. B. thuringiensis isolate JK12 exhibited higher toxicity against H. armigera than that of B. thuringiensis HD1, hence can be commercially exploited to control insect pest for sustainable crop production. The results of this study confirm the significance of continuous exploration of new Bt stains from different ecological regions of the world.

The First Cry2Ac-Type Protein Toxic to Helicoverpa armigera: Cloning and Overexpression of Cry2ac7 Gene from SBS-BT1 Strain of Bacillus thuringiensis

The Cry (crystal) proteins from Bacillus thuringiensis are known to have toxicity against a variety of insects and have been exploited to control insect pests through transgenic plants and biopesticides. B. thuringiensis SBS BT-1 carrying the cry2 genes was isolated from soil samples in Pakistan. The 2-kb full length cry2Ac gene was cloned, sequenced, and submitted to the EMBL DNA database (Accession No. AM292031). For expression analysis, Escherichia coli DH5α was transformed with the fragment sub-cloned in pET22b expression vector using NdeI and HindIII restriction sites, and later confirmed by restriction endonuclease analysis. To assess the toxicity of Cry2Ac7 protein against lepidopteran and dipteran insects, BL21 (codon plus) strain of E. coli was further transformed with the recombinant plasmid. The 65-kDa protein was expressed in the form of inclusion bodies up to 180 OD units per liter of the medium. Inclusions were washed with a buffer containing 1.5% Triton-X 100 and >90% pure Cry2Ac7 was obtained. The inclusion bodies were dissolved in 50 mM K₂CO₃ (pH 11.5), dialyzed, and freeze-dried. This freeze-dried protein as well as inclusion bodies were used in bioassays against larvae of Helicoverpa armigera and Musca domestica. The freeze-dried protein was toxic to H. armigera larvae with an LC₅₀ value of 131 ng/mL. However, Cry2Ac7 produced in E. coli did not show any mortality to M. domestica larvae. This is the first report of Cry2Ac protein toxic to H. armigera.

A natural hybrid of a Bacillus thuringiensis Cry2A toxin implicates Domain I in specificity determination

A PCR-RFLP method was used to identify cry2A toxin genes in a collection of 300 strains of Bacillus thuringiensis. From 81 genes identified, the vast majority appeared to be cry2Aa or cry2Ab, however three showed a different pattern and were subsequently cloned and sequenced. The gene cloned from strain HD395 was named cry2Ba2. Since the proteins encoded by the genes cloned from LS5115-3 and DS415 shared >95% sequence identity with existing toxins their genes were named cry2Aa17 and cry2Ab29 respectively by the toxin nomenclature committee. Despite this overall similarity these two toxins resembled natural hybrids, with Cry2Ab29 resembling Cry2Ab for the majority of the protein but then showing identity to Cry2Aa for the last 66 amino acids. For Cry2Aa17, Domains II and III most closely resembled Cry2Aa (99% identity) whilst Domain I was identical to that of Cry2Ab. The toxicity of the recombinant toxins was tested against Aedes aegypti and Spodoptera exigua, and it was found that the toxicity profile of Cry2Aa17 more closely matched the profile of Cry2Ab than that of Cry2Aa, thus implicating Domain I in specificity determination. This association of Domain I with toxicity was confirmed when hybrids were made between Cry2Aa and Cry2Ab.

Diversity and distribution of lepidopteran-specific toxin genes in Bacillus thuringiensis strains from Argentina

A total of 268 Bacillus thuringiensis strains obtained from different sources of Argentina were analyzed to determine the diversity and distribution of the cry1, cry2, cry8, cry9 and vip3A genes encoding for lepidopteran-specific insecticidal proteins. Twin strains were excluded. Ten different profiles were detected among the 80 selected B. thuringiensis strains. Two of these profiles (cry1Aa, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa (35/80), and cry1Aa, cry1Ab, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa (25/80)) pooled 75% of the strains. The existence of this low diversity is rare, since in most of the studied collections a great diversity of insecticidal toxin gene profiles has been described. In addition, the most frequently detected profile was also most frequently derived from soil (70%), stored product dust (59%) and spider webs (50%). In contrast, the cry1Aa, cry1Ab, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa profiles were mainly detected in strains isolated from leaves (40%) and dead insect larvae (50%). Six of the identified insecticidal toxin gene profiles were discovered in strains isolated from stored product dust and leaves indicating higher diversity of profiles in these kinds of sources than in others. Some strains with high insecticidal activity against Epinotia aporema (Lepidoptera) larvae were identified, which is important to explore future microbial strategies for the control of this crop pest in the region.

Molecular characterization of indigenous Bacillus thuringiensis strains isolated from Kashmir valley

Bacillus thuringiensis (Bt) being an eco-friendly bioinsecticide is effectively used in pest management strategies and, therefore, isolation and identification of new strains effective against a broad range of target pests is important. In the present study, new indigenous B. thuringiensis strains were isolated and investigated so that these could be used as an alternative and/or support the current commercial strains/cry proteins in use. For this, 159 samples including soil, leaf and spider webs were collected from ten districts of Kashmir valley (India). Of 1447 bacterial strains screened, 68 Bt strains were identified with 4 types of crystalline inclusions. Crystal morphology ranking among the Bt strains was spherical (69.11%) > spore attached (8.82%) > rod (5.88%) = bipyramidal (5.88%) > spherical plus rod (4.41%) > spherical plus bipyramidal (2.94%) = cuboidal (2.94%). SDS-PAGE investigation of the spore-crystal mixture demonstrated Bt strains contained proteins of various molecular weights ranging from 150 to 28 kDa. Insecticidal activity of the 68 indigenous Bt strains against Spodoptera litura neonates showed that Bt strain SWK1 strain had the highest mortality. Lepidopteron active genes (cry1, cry2Ab, cry2Ab) were present in six Bt strains. Further, analysis of a full-length cry2A gene (~1.9 kb) by PCR-RFLP in strain SWK1 revealed that it was a new cry2A gene in Bt strain SWK1 and was named as cry2Al1 (GenBank Accession No. KJ149819.1) using the Bt toxin nomenclature ( http://www.btnomenclature.info ). Insect bioassays with neonate larvae of S. litura and H. armigera showed that the purified Cry2Al1 is toxic to S. litura with LC₅₀ 2.448 µg/ml and H. armigera with LC₅₀ 3.374 µg/ml, respectively. However, it did not produce any mortality in third instar larvae of Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi larvae/pupae insects (100 µg/ml) at 28 ± 2 °C and 75 to 85% relative humidity under a photoperiod of 14L:10D.

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.

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

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

Selection and Characterization of Bacillus thuringiensis (Berliner) (Eubacteriales: Bacillaceae) Strains for Ecdytolopha aurantiana (Lima) (Lepidoptera: Tortricidae) Control

The citrus fruit borer, Ecdytolopha aurantiana (Lima, 1927) (Lepidoptera: Tortricidae), is responsible for major losses to the citrus industry because it causes rot and drop of fruits. The current study aimed to select and characterize Bacillus thuringiensis (Berliner, 1911) strains toxic to E. aurantiana. For this purpose, 47 B. thuringiensis strains were evaluated in selective bioassays using first instar larvae of E. aurantiana. The lethal concentration (LC₅₀) of the most toxic strains was estimated, and the strains were characterized by morphological, biochemical, and molecular methods. Of the 47 strains tested, 10 caused mortality above 85% and showed mean lethal concentrations between 1.05E+7 and 1.54E+8 spores mL^-1. The lowest LC₅₀ values were obtained for the HD-1 standard strain and the BR145, BR83, BR52, and BR09 strains. The protein profile showed the presence of Cry proteins of 60, 65, 70, 80, and 130 kDa. The molecular characterization showed the presence of cry1, cry2, cry3, and cry11 genes. The morphological analysis identified three different crystalline inclusions: bipyramidal, round, and cuboidal. The cry1 and cry2 genes were the most frequent among the B. thuringiensis strains evaluated and encode Cry proteins toxic to insects of the order Lepidoptera, which agree with the toxicity results obtained by the selective bioassays against E. aurantiana. The results showed four different B. thuringiensis strains toxic to E. aurantiana at the same level as the HD-1 standard strain, and these strains have biotechnological potential for E. aurantiana control through the production of transgenic plants or the formulation of biopesticides.

Prevalence of cry2-type genes in Bacillus thuringiensis isolates recovered from diverse habitats in India and isolation of a novel cry2Af2 gene toxic to Helicoverpa armigera (cotton boll worm)

Insecticidal cry and vip genes from Bacillus thuringiensis (Bt) have been used for control of lepidopteran insects in transgenic crops. However, novel genes are required for gene pyramiding to delay evolution of resistance to the currently deployed genes. Two PCR-based techniques were employed for screening of cry2-type genes in 129 Bt isolates from diverse habitats in India and 27 known Bt strains. cry2Ab-type genes were more prevalent than cry2Aa- and cry2Ac-type genes. Correlation between source of isolates and abundance of cry2-type genes was not observed. Full-length cry2A-type genes were amplified by PCR from 9 Bt isolates and 4 Bt strains. The genes from Bt isolates SK-758 from Sorghum grain dust and SK-793 from Chilli seeds warehouse, Andhra Pradesh, were cloned and sequenced. The gene from SK-758 (NCBI GenBank accession No. GQ866915) was novel, while that from SK-793 (NCBI GenBank accession No. GQ866914) was identical to the cry2Ab1 gene. The Bacillus thuringiensis Nomenclature Committee ( http://www.lifesci.sussex.ac.uk/home/Neil_Crickmore/Bt/toxins2.html ) named these genes cry2Af2 and cry2Ab16, respectively. The cry2Af2 gene was expressed in Escherichia coli and found to be toxic towards Helicoverpa armigera. The cry2Af2 gene will be useful for pyramiding in transgenic crops.

Diversity and Toxicity of Bacillus thuringiensis from Shifting Cultivation (Jhum) Habitat

Bacillus thuringiensis (Bt) strains were isolated from jhum-agriculture, jhum-forest, aquatic and fallow soil samples from Mizoram by acetate selection method. Isolates were characterized for biochemical typing, cry gene and protein profiling, growth curve study and toxicity against Culex tritaeniorhynchus. Bt frequency was high in jhum-agriculture land (69.56%) whereas low in jhum-forest soils (31.57%). Bt was found to be abundant in jhum shifting cultivation soil with an index ranging between 0.010 and 0.015. Majority of the isolates from jhum soils produced oval and spherical crystals and showed eleven types of crystal proteins groups. PCR analysis revealed predominance of dipteran-active cry genes (cry4 and cry9). The variations in crystal morphology, cry genes and Cry protein (s) from the isolates of Bt revealed molecular diversity. Higher mortality, lower lethal dose, and lesser time to kill were observed in Bt isolates from jhum soils than aquatic and fallow habitats. Based on the toxicity test, SC1 and HP7 isolates containing cry 4 and cry 9 genes showed higher activity. Growth curve analysis showed significant variations among Bt isolates to reach the sporulating stage. Higher growth index and lower mean generation time were observed in SC1 and HP7 Bt isolates. Bt strains express different endotoxin genes and crystal proteins and their harvesting time also varied from strain to strain. Significant variation was found in Bt isolates from jhum habitats in relation to the cry gene composition, protein profiling and toxicity. Results from this study suggest that novel Bt entomopathogens may complement for regulating mosquito vectors.

Probiotic Bacillus cereus Strains, a Potential Risk for Public Health in China

Bacillus cereus is an important cause of foodborne infectious disease and food poisoning. However, B. cereus has also been used as a probiotic in human medicine and livestock production, with low standards of safety assessment. In this study, we evaluated the safety of 15 commercial probiotic B. cereus preparations from China in terms of mislabeling, toxin production, and transferable antimicrobial resistance. Most preparations were incorrectly labeled, as they contained additional bacterial species; one product did not contain viable B. cereus at all. In total, 18 B. cereus group strains-specifically B. cereus and Bacillus thuringiensis-were isolated. Enterotoxin genes nhe, hbl, and cytK1, as well as the ces-gene were assessed by PCR. Enterotoxin production and cytotoxicity were confirmed by ELISA and cell culture assays, respectively. All isolated B. cereus group strains produced the enterotoxin Nhe; 15 strains additionally produced Hbl. Antimicrobial resistance was assessed by microdilution; resistance genes were detected by PCR and further characterized by sequencing, transformation and conjugation assays. Nearly half of the strains harbored the antimicrobial resistance gene tet(45). In one strain, tet(45) was situated on a mobile genetic element-encoding a site-specific recombination mechanism-and was transferable to Staphylococcus aureus and Bacillus subtilis by electro-transformation. In view of the wide and uncontrolled use of these products, stricter regulations for safety assessment, including determination of virulence factors and transferable antimicrobial resistance genes, are urgently needed.

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.

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.

Chromosome-Directed PCR-Based Detection and Quantification of Bacillus cereus Group Members with Focus on B. thuringiensis Serovar israelensis Active against Nematoceran Larvae

Bacillus thuringiensis serovar israelensis is a wide-spread soil bacterium affiliated with the B. cereus group (Bcg) and is widely used in biocontrol products applied against mosquito and black fly larvae. For monitoring and quantification of applied B. thuringiensis serovar israelensis and its effect on indigenous B. thuringiensis serovar israelensis and Bcg assemblages, efficient and reliable tools are essential. The abundance and properties of B. thuringiensis serovar israelensis strains in the environment traditionally have been investigated with cultivation-dependent techniques, which are hampered by low sensitivity and the morphological similarity between B. cereus and B. thuringiensis. Currently available PCR-based detection and quantification tools target markers located on plasmids. In this study, a new cultivation-independent PCR-based method for efficient and specific quantification of B. thuringiensis serovar israelensis and Bcg is presented, utilizing two sets of PCR primers targeting the bacterial chromosome. Sequence database searches and empirical tests performed on target and nontarget species, as well as on bulk soil DNA samples, demonstrated that this diagnostic tool is specific for B. thuringiensis serovar israelensis and Bcg. The method will be useful for comparisons of Bcg and B. thuringiensis serovar israelensis abundances in the same samples. Moreover, the effect of B. thuringiensis serovar israelensis-based insecticide application on the total Bcg assemblages, including indigenous populations, can be investigated. This type of information is valuable in risk assessment and policy making for use of B. thuringiensis serovar israelensis in the environment.

Bacillus thuringiensis toxins: an overview of their biocidal activity

Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities.

Characterization of parasporin gene harboring Indian isolates of Bacillus thuringiensis

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

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.

Mining rare and ubiquitous toxin genes from a large collection of Bacillus thuringiensis strains

There has been considerable effort made in recent years for research groups and other organizations to build up large collections of strains of Bacillus thuringiensis in the search for genes encoding novel insecticidal toxins, or encoding novel metabolic pathways. Whilst next generation sequencing allows the detailed genetic characterization of a bacterial strain with relative ease it is still not practicable for large strain collections. In this work we assess the practicability of mining a mixture of genomic DNA from a two thousand strain collection for particular genes. Using PCR the collection was screened for both a rare (cry15) toxin gene as well as a more commonly found gene (vip3A). The method was successful in identifying both a cry15 gene and multiple examples of the vip3A gene family including a novel member of this family (vip3Aj). A number of variants of vip3Ag were cloned and expressed, and differences in toxicity observed despite extremely high sequence similarity.

The basis for rootstock resilient to Capnodis species: screening for genes encoding δ-endotoxins from Bacillus thuringiensis

BACKGROUND

Conventional methods often fail to control the flatheaded borers Capnodis spp., major pests of stone fruit trees; the larvae are protected from insecticides and predation because they feed deep in the roots. A potential solution is transgenic trees producing in their roots toxic compounds such as Cry proteins of Bacillus thuringiensis (Bt).

RESULTS

Toxicities against Capnodis larvae were demonstrated by exploiting a recently designed artificial larval diet and an available collection of field isolated Bt. An isolate of Bt tenebrionis (Btt) from commercial bioinsecticide (Novodor) displayed LC50 and LC95 values of 3.2 and 164 mg g(-1) , respectively, against neonates of Capnodis tenebrionis, whereas values of the most toxic field isolate K-7 were 1.9 and 25.6 mg g(-1) respectively. Weights of surviving larvae after 1 month on diets containing low concentrations of K-7 (0.1-1.0 mg g(-1) ) were lower than on Btt or untreated larvae. K-7 was also toxic against larvae of C. cariosa and C. miliaris and found to harbour genes encoding Cry9Ea-like and Cry23Aa/Cry37Aa binary toxins.

CONCLUSION

Larvae of Capnodis spp. are susceptible to Bt Cry toxins. Expressing cry genes active against these pests thus seems a feasible solution towards production of transgenic rootstock trees resilient to the pest.

Bacillus thuringiensis HD-1 Cry- : development of a safe, non-insecticidal simulant for Bacillus anthracis

AIMS

A representative simulant for spores of Bacillus anthracis is needed for field testing. Bacillus thuringiensis is gaining recognition as a suitable organism. A strain that does not form the insecticidal, parasporal crystals that are characteristic of this species is a more accurate physical representative of B. anthracis spores. We developed noninsecticidal derivatives of two isolates of B. thuringiensis HD-1.

METHODS AND RESULTS

Two plasmid-cured derivatives of B. thuringiensis HD-1, unable to make crystal toxins ('Cry(-) '), were isolated. These isolates and the existing Cry(-) strain, B. thuringiensis Al Hakam, were probed with PCR assays against the known insecticidal genes cry, vip and cyt. Their genomic DNA was sequenced to demonstrate a lack of insecticidal genes. This was confirmed by bioassays against a number of invertebrate species. Real-time PCR assays were developed to identify the B. thuringiensis HD-1 Cry(-) derivatives and an effective differential and selective medium was assessed.

CONCLUSIONS

All three Cry(-) isolates are devoid of known insecticidal determinants. The B. thuringiensis HD-1 Cry(-) derivatives can easily be recovered from soil and identified by PCR with some selectivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The B. thuringiensis HD-1 Cry(-) derivatives represent accurate, nongenetically manipulated simulants for B. anthracis with excellent human and environmental safety records.

Proteomics study of silver nanoparticles toxicity on Bacillus thuringiensis

Emerging technologies in functional genomics and proteomics provide a way of achieving high-throughput analyses, understanding effects on protein populations and sub-populations and follow up environmental stresses. To accomplish these, the action of homemade spherical Silver nanoparticles colloidal suspension (AgNPs) against Bacillus thuringiensis (isolate from Oryza sativa L. rhizosphere) was investigated by a proteomic approach (2-DE and NanoLC/FT-ICR MS identification). Thirty four responsive (up/down regulated) proteins were identified. Proteomic results revealed that an exposure of B. thuringiensis cells with different concentrations of AgNPs resulted in an accumulation of envelope protein precursors, indicative of the dissipation of a proton motive force. Identified proteins are involved in oxidative stress tolerance, metal detoxification, transcription and elongation processes, protein degradation, cytoskeleton remodeling and cell division. The expression pattern of these proteins and their possible involvement in the nontoxicity mechanisms were discussed.