Thuringiensis Crystal Protein Research Articles

Bacillus thuringiensis Cry14A family proteins as novel anthelmintics against gastrointestinal nematode parasites.

Bacillus thuringiensis crystal (Cry) proteins have been expressed in commercial transgenic crops for nearly 30 years, providing safe and effective control of insect pests and significantly reducing the application of hazardous chemical pesticides. B. thuringiensis crystal proteins have also been shown to target parasitic nematodes, including plant parasitic nematodes. Recently, transgenic soybean crops expressing Cry14Ab have been shown to provide control against the soybean cyst nematode Heterodera glycines, marking the first time a crystal protein is being commercialized in transgenic crops for control of a nematode pest. However, apart from H. glycines and the free-living nematode, Caenornabditis elegans, the breadth of nematode activity of Cry14Ab, e.g., against gastrointestinal parasitic nematodes (GINs), has not been reported. Here we study the efficacy of Cry14Ab against a wide range of gastrointestinal nematode parasites (GINs) in vitro and in vivo. We find that Cry14Ab is effective in vitro against the barber's pole worm Haemonchus contortus larvae, small strongyles cyathostomin larvae, the hookworm Ancylostoma ceylanicum adults, the roundworm Ascaris suum L4 larvae, and the whipworm Trichuris muris adults. In rodents infected with GIN parasites, Cry14Ab is effective as an in vivo anthelmintic against the hookworms A. ceylanicum and N. americanus, against the mouse parasite Heligmosomoides polygyrus bakeri, and against the roundworm A. suum. Cry14Ab also variably reduces the reproduction of the whipworm T. muris in vivo. Using optimized profile Markov Models, we looked for other putative anthelmintic Cry proteins and, within this list, identified a Bt crystal protein, GenBank accession no. MF893203, that we produced and demonstrated intoxicated GINs. This protein, with 90% amino acid identity to Cry14Ab, is active against C. elegans, A. ceylanicum adults, and A. suum L4 larvae in vitro. MF893203 was given the official designation of Cry14Ac. Cry14Ac is also an effective in vivo anthelmintic against A. ceylanicum hookworms in hamsters and intestinal A. suum in mice. Taken together, our results demonstrate that Cry14Ab and Cry14Ac have wide therapeutic utility against GINs.

Resistance to Cry14A family Bacillus thuringiensis crystal proteins in Caenornabditis elegans operates via the nhr-31 transcription factor and vacuolar-type ATPase pathway.

Bacillus thuringiensis (Bt) has been successfully used commercially for more than 60 years for biocontrol of insect pests. Since 1996, transgenic plants expressing Bt crystal (Cry) proteins have been used commercially to provide protection against insects that predate on corn and cotton. More recently, Bt Cry proteins that target nematodes have been discovered. One of these, Cry14Ab, has been expressed in transgenic soybean plants and found to provide significant protection against the soybean cyst nematode, Heterodera glycines. However, to date there has been no description of high-level resistance to any Cry14A family protein in nematodes. Here, we describe forward genetic screens to identify such mutants using the nematode Caenorhabditis elegans. Although non-conditional screens failed to identify highly resistant C. elegans, a conditional (temperature-sensitive) genetic screen identified one mutant, bre-6(ye123) (for Bt protein resistant), highly resistant to both Cry14Aa and Cry14Ab. The mutant comes at a high fitness cost, showing significant delays in growth and development and reduced fecundity. bre-6(ye123) hermaphrodites are only weakly resistant to copper intoxication, indicating that the mutant is not highly resistant to all insults. Backcrossing-whole genome sequencing was used to identify the gene mutated in ye123 as the nuclear hormone receptor nhr-31. RNAi, DNA rescue, and CRISPR analyses confirm that resistance to Cry14Aa intoxication in bre-6(ye123) is due to mutation of nhr-31 and was renamed nhr-31(ye123). As predicted for a mutation in this gene, nhr-31(ye123) animals showed significantly reduced expression of most of the subunits of the C. elegans vacuolar ATPase (vATPase). Mutants in the vATPase subunits unc-32 and vha-7 also show resistance to Cry14Aa and/or Cry14Ab. These data demonstrate that nhr-31 and the vATPase play a significant role in the intoxication of C. elegans by Cry14A family proteins, that reduction in vATPase levels result in high resistance to Cry14A family proteins, and that such resistance comes at a high fitness cost. Based on the relative difficulty of finding resistant mutants and the fitness cost associated with the vATPase pathway, our data suggest that transgenic Cry14Ab plants may hold up well to resistance by nematode parasites.

Molecular Identification of Hyalomma Ticks and Application of Bacillus thuringiensis Toxins as an Effective Biological Acaricide.

Bacillus thuringiensis (B. thuringiensis) is considered one of the most important entomopathogenic microorganisms. It produces potent toxins against insects. Therefore, the present study investigates the bioacaricidal properties of B. thuringiensis on the Hyalomma tick species. Firstly, we identify Hyalomma ticks based on morphological screening and molecular characterization. The cytochrome C oxidase subunit I (COX1) gene was selected for the polymerase chain reaction (PCR) analysis, which resulted in the amplification of 656 bp. The amplified products were sequenced, and the isolated (COX1) gene of ticks was submitted to the gene bank of NCBI (Accession No. OR077934.1). The nucleotide sequences were retrieved from the NCBI data bank by BLASTn analysis, which confirmed that all obtained sequences belong to genus Hyalomma, and multiple alignments confirmed that the sequence of Hyalomma anatolicum Tandojam-isolate (HA-TJ) 100% aligned with Hyalomma analoticum KP792577.1, Hyalomma detritum KP792595.1, Hyalomma excavatum KX911989.1, and H. excavatum OQ449693.1. The generated phylogenetic tree confirmed that sequences of HA-TJ COX1 clustered with a single clad of H. analoticum, H. excavatum, and H. detritum. The acaricidal effect of B. thuringiensis toxins B. thuringiensis spore crystal mix (BtSCM) and B. thuringiensis crystal proteins (Btcps) was evaluated against larvae and adult life stages of Hyalomma ticks in vitro. We applied Btcps and BtSCM separately with different concentrations and calculated the mortality percentage. Adult mortality was estimated at the 8th, 10th, 12th, and 15th days posttreatment and larval mortality after 24 h. During treatment of the adult life stage, at first, ticks were immersed in different concentrations of Btcps and BtSCM for 5 min after the treatments, and the samples were transferred to sterile containers and placed in an incubator with 80% humidity at 23°C. Furthermore, Btcps produced the highest mortality on Day 15, 89 ± 1.00% at a concentration of 3000 μg/mL, followed by the 12th, 10th, and 8th days produced 83 ± 1.91%, 70 ± 1.15%, and 61 ± 1.00%, respectively. BtSCM produced mortality of 69 ± 1.91% on Day 15 at a concentration of 3000 μg/mL, followed by the 12th, 10th, and 8th days at 57 ± 2.51%, 37 ± 1.91%, and 34 ± 2.00%. The present study revealed that B. thuringiensis toxins produced a significant (p < 0.05) increase in mortality rate in adults of Hyalomma ticks. Additionally, Btcps and BtSCM were used to treat the larval stage. The treatments were applied to calculate the mortality percentage via the Laravel packet test. At a 1500 μg/mL concentration, Btcps resulted in the highest mortality of 98 ± 1.15%; this was followed by 1250 μg/mL, 1000 μg/mL, and 750 μg/mL, which produced mortalities of 76 ± 1.63%, 60 ± 1.63%, and 56 ± 1.63%, respectively. In addition, BtSCM produced a mortality rate of 79 ± 2.51% at a concentration of 1500 μg/mL. Furthermore, 75 ± 2.51%, 65 ± 1.91%, and 58 ± 1.15% mortality were observed at concentrations of 1250 μg/mL, 1000 μg/mL, and 750 μg/mL, respectively. The results showed a significant (p < 0.05) increase in larval mortality compared to the control group. We conclude that B. thuringiensis toxins are applicable as a bioacaricide.

Gut Microbiota Accelerate the Insecticidal Activity of Plastid-Expressed Bacillus thuringiensis Cry3Bb to a Leaf Beetle, Plagiodera versicolora.

Bacillus thuringiensis is widely used as a biopesticide, and its crystal protein expressed in transgenic crops has been successfully used for the management of insect pests. However, whether the midgut microbiota contribute to the Bt insecticidal mechanism remains controversial. We previously demonstrated that transplastomic poplar plants expressing Bt Cry3Bb are highly lethal to willow leaf beetle (Plagiodera versicolora), one of the major pests causing severe damage to Salicaceae plants such as willows and poplars. Here, we demonstrate that feeding poplar leaves expressing Cry3Bb to nonaxenic P. versicolora larvae leads to significantly accelerated mortality, and overgrowth and dysbiosis of the gut microbiota, compared with axenic larvae. Corroborating work done with Lepidopteran insects, plastid-expressed Cry3Bb can cause the lysis of the beetle's intestinal cells, lead to the entry of intestinal bacteria into the body cavity, and thus cause the dynamic changes in the flora of the midgut and blood cavity in P. versicolora. Reintroduction of Pseudomonas putida, a gut bacterium of P. versicolora, into axenic P. versicolora larvae further enhances mortality upon feeding on Cry3Bb-expressing poplar. Our results indicate the important contribution of host gut microbiota in promoting the B. thuringiensis crystal protein insecticidal activity and provide new insights into the mechanism of pest control by Bt-transplastomic approaches. IMPORTANCE The contribution of gut microbiota to Bacillus thuringiensis Cry3Bb insecticidal activity in a leaf beetle was demonstrated using transplastomic poplar plants, providing a potential new approach to improve the efficiency of plastid transformation technology for pest control by expression of Bt toxins.

Efficient and Scalable Process to Produce Novel and Highly Bioactive Purified Cytosolic Crystals from Bacillus thuringiensis.

ABSTRACTBacillus thuringiensis (Bt) is a Gram-positive soil bacterium that is widely and safely applied in the environment as an insecticide for combatting insect pests that damage crops or are disease vectors. Dominant active ingredients made by Bt are insect-killing crystal (Cry) proteins released as crystalline inclusions upon bacterial sporulation. Some Bt Cry proteins, e.g., Cry5B (formally Cry5Ba1), target nematodes (roundworms) and show exceptional promise as anthelmintics (cures for parasitic nematode diseases). We have recently described inactivated bacteria with cytosolic crystal(s) (IBaCC) in which bioactive Bt Cry crystals (containing Cry5B) are fully contained within the cytosol of dead bacterial ghosts. Here, we demonstrate that these IBaCC-trapped Cry5B crystals can be liberated and purified away from cellular constituents, yielding purified cytosolic crystals (PCC). Cry5B PCC contains ~95% Cry5B protein out of the total protein content. Cry5B PCC is highly bioactive against parasitic nematode larvae and adults in vitro. Cry5B PCC is also highly active in vivo against experimental human hookworm and Ascaris infections in rodents. The process was scaled up to the 100-liter scale to produce PCC for a pilot study to treat two foals infected with the ascarid Parascaris spp. Single-dose Cry5B PCC brought the fecal egg counts of both foals to zero. These studies describe the process for the scalable production of purified Bt crystals and define a new and attractive pharmaceutical ingredient form of Bt Cry proteins.IMPORTANCE Bacillus thuringiensis crystal proteins are widely and safely used as insecticides. Recent studies have shown they also can cure gastrointestinal parasitic worm (nematode) infections when ingested. However, reproducible, scalable, and practical techniques for purifying these proteins have been lacking. Here, we address this severe limitation and present scalable and practical methods for large-scale purification of potently bioactive B. thuringiensis crystals and crystal proteins. The resultant product, called purified cytosolic crystals (PCC), is highly compatible with ingestible drug delivery and formulation. Furthermore, there are growing applications in agriculture and insect control where access to large quantities of purified crystal proteins is desirable and where these methods will find great utility.

A new paraprobiotic-based treatment for control of Haemonchus contortus in sheep

Haemonchus contortus is a critical parasite of goats and sheep. Infection by this blood-feeding gastrointestinal nematode (GIN) parasite has significant health consequences, especially in lambs and kids. The parasite has developed resistance to virtually all known classes of small molecule anthelmintics used to treat it, giving rise in some areas to multidrug resistant parasites that are very difficult to control. Thus, new anthelmintics are urgently needed. Bacillus thuringiensis (Bt) crystal protein 5B (Cry5B), a naturally occurring protein made by a bacterium widely and safely used around the world as a bioinsecticide, represents a new non-small molecule modality for treating GINs. Cry5B has demonstrated anthelmintic activities against parasites of monogastric animals, including some related to those that infect humans, but has not yet been studied in a ruminant. Here we show that H. contortus adults are susceptible to Cry5B protein in vitro. Cry5B produced in its natural form as a spore-crystal lysate against H. contortus infections in goats had no significant efficacy. However, a new Active Pharmaceutical Ingredient (API) paraprobiotic form of Cry5B called IBaCC (Inactivated Bacterium with Cytosolic Crystals), in which Cry5B crystals are encapsulated in dead Bt cell wall ghosts, showed excellent efficacy in vitro against larval stages of H. contortus and relative protein stability in bovine rumen fluid. When given to sheep experimentally infected with H. contortus as three 60 mg/kg doses, Cry5B IBaCC resulted in significant reductions in fecal egg counts (90%) and parasite burdens (72%), with a very high impact on female parasites (96% reduction). These data indicate that Cry5B IBaCC is a potent new treatment tool for small ruminants in the battle against H. contortus.

Bacillus thuringiensis Cry5B is Active against Strongyloides stercoralis in vitro.

Strongyloidiasis, caused by Strongyloides stercoralis infection, is an important neglected tropical disease that causes significant public health problems in the tropics and subtropics. The disease can persist in hosts for decades and may be life-threatening because of hyperinfection and dissemination. Ivermectin (mostly) and albendazole are the most common anthelmintics used for treatment. Albendazole is suboptimal for this parasite, and although ivermectin is quite effective in immunocompromised patients, a multiple-course regimen is required. Furthermore, reliance on a single drug class for treating intestinal nematodes is a recipe for future failure. Therefore, it is important to discover new anthelmintics to treat or prevent human strongyloidiasis. One promising candidate is the Bacillus thuringiensis crystal protein Cry5B. Cry5B is highly potent against parasitic nematodes, for example, hookworms and Ascaris suum. Here, we investigated the potential of Cry5B against S. stercoralis. Multiple stages of S. stercoralis, including the first larval stage (L1s), infective stage (iL3s), free-living adult stage, and parasitic female stage, were all susceptible to Cry5B as indicated by impairment of motility and decreased viability in vitro. In summary, Cry5B demonstrated strong potential as an effective anthelmintic for treatment and transmission control of human strongyloidiasis, justifying further experiments to investigate in vivo therapeutic efficacy.

The role of membrane-bound metal ions in toxicity of a human cancer cell-active pore-forming toxin Cry41Aa from Bacillus thuringiensis

Bacillus thuringiensis crystal (Cry) proteins, used for decades as insecticidal toxins, are well known to be toxic to certain insects, but not to mammals. A novel group of Cry toxins called parasporins possess a strong cytocidal activity against some human cancer cells. Cry41Aa, or parasporin3, closely resembles commercially used insecticidal toxins and yet is toxic to the human hepatic cancer cell line HepG2, disrupting membranes of susceptible cells, similar to its insecticidal counterparts. In this study, we explore the protective effect that the common divalent metal chelator EGTA exerts on Cry41Aa's activity on HepG2 cells. Our results indicate that rather than interfering with a signalling pathway as a result of chelating cations in the medium, the chelator prevented the toxin's interaction with the membrane, and thus the subsequent steps of membrane damage and p38 phosphorylation, by removing cations bound to plasma membrane components. BAPTA and DTPA also inhibited Cry41Aa toxicity but at higher concentrations. We also show for the first time that Cry41Aa induces pore formation in planar lipid bilayers. This activity is not altered by EGTA, consistent with a biological context of chelation. Salt supplementation assays identified Ca2+, Mn2+ and Zn2+ as being able to reinstate Cry41Aa activity. Our data suggest the existence of one or more metal cation-dependent receptors in the Cry41Aa mechanism of action.

In vivo and in vitro studies of Cry5B and nicotinic acetylcholine receptor agonist anthelmintics reveal a powerful and unique combination therapy against intestinal nematode parasites.

BackgroundThe soil-transmitted nematodes (STNs) or helminths (hookworms, whipworms, large roundworms) infect the intestines of ~1.5 billion of the poorest peoples and are leading causes of morbidity worldwide. Only one class of anthelmintic or anti-nematode drugs, the benzimidazoles, is currently used in mass drug administrations, which is a dangerous situation. New anti-nematode drugs are urgently needed. Bacillus thuringiensis crystal protein Cry5B is a powerful, promising new candidate. Drug combinations, when properly made, are ideal for treating infectious diseases. Although there are some clinical trials using drug combinations against STNs, little quantitative and systemic work has been performed to define the characteristics of these combinations in vivo.Methodology/Principal findingsWorking with the hookworm Ancylostoma ceylanicum-hamster infection system, we establish a laboratory paradigm for studying anti-nematode combinations in vivo using Cry5B and the nicotinic acetylcholine receptor (nAChR) agonists tribendimidine and pyrantel pamoate. We demonstrate that Cry5B strongly synergizes in vivo with both tribendimidine and pyrantel at specific dose ratios against hookworm infections. For example, whereas 1 mg/kg Cry5B and 1 mg/kg tribendimidine individually resulted in only a 0%-6% reduction in hookworm burdens, the combination of the two resulted in a 41% reduction (P = 0.020). Furthermore, when mixed at synergistic ratios, these combinations eradicate hookworm infections at doses where the individual doses do not. Using cyathostomin nematode parasites of horses, we find based on inhibitory concentration 50% values that a strongylid parasite population doubly resistant to nAChR agonists and benzimidazoles is more susceptible or “hypersusceptible” to Cry5B than a cyathostomin population not resistant to nAChR agonists, consistent with previous Caenhorhabditis elegans results.Conclusions/SignificanceOur study provides a powerful means by which anthelmintic combination therapies can be examined in vivo in the laboratory. In addition, we demonstrate that Cry5B and nAChR agonists have excellent combinatorial properties—Cry5B combined with nAChR agonists gives rise to potent cures that are predicted to be recalcitrant to the development of parasite resistance. These drug combinations highlight bright spots in new anthelmintic development for human and veterinary animal intestinal nematode infections.

Identification of a new binding protein in the insect-pest midgut Heliothis virescens that interacts with Cry1A toxins

Bacillus thuringiensis crystal protein family (Cry) consists of a diverse group of proteins with activity against insects of different orders, such as the Lepidoptera members. Their primary action is to lyse midgut epithelial cells by inserting into the target membrane and forming pores. Among this group, members of Cry1A family are used worldwide for insect control, and their mode of action has been characterized in some detail, although it is not completely known. Cry1A-binding proteins detected on ligand blots of insect brush border membrane vesicles (BBMV) have been identified as members of the aminopeptidase N and cadherin families, although the relative role of the two putative receptor molecules in insects has yet to be conclusively determined. Moreover, it seems that there are other proteins in the midgut cell surface of insect-pests that can interact with Cry1Ac, leading to cell death. Therefore, in this report, we identified the gamma region of a G-protein from Heliothis virescens (HvgGP) as a potential receptor for Cry1Ac. Hence, using in silico analyses, we determined the structure of HvgGP and its interaction region with Cry1Ac. The binding sites was confirmed through Phage Display assays, using both Cry1Ac and HvgGP as templates. Fluorescence analyses indicated that HvgGP interacts with Cry1Ac in a specific region. Although the mode of action through membrane pore formation was already confirmed by several in vivo and in vitro assays, the mechanism through inhibition/activation of signalling pathways by the interaction with G protein complexes is still not clear. Considering the importance of G proteins on the activation of several signaling pathways and the role of Cry toxins in the agribussiness, we also propose a new mechanism of action for Cry1Ac, using HvgGP as the binding protein.

Characterization and regulation of Bacillus thuringiensis Cry toxin binding aminopeptidases N (APNs) from non-gut visceral tissues, Malpighian tubule and salivary gland: Comparison with midgut-specific APN in the moth Achaea janata

Bacillus thuringiensis (Bt) crystal proteins (Cry) bind to aminopeptidase N (APN) receptors on insect midgut membrane leading to pore formation and subsequent death. However, evolution of insect resistance to Bt toxins threatens their long-term application. Therefore, search for new targets which could function as Cry toxin receptors is an immediate mandate. In the present study, two full-length APN cDNAs were cloned from Malpighian tubule and salivary gland tissues of the moth, Achaea janata. Both these APNs showed 99% and 32% sequence homology with fat body and midgut APNs respectively. Tissue distribution analysis revealed the presence of two different APN isoforms, one predominant in non-gut visceral tissues while the other exclusively expressed in the midgut. Immunofluorescence and western blot analyses showed cross-reactivity in Malpighian tubule and salivary gland when probed with anti-fat body APN antiserum. These results clearly indicated the presence of non-gut (AjAPN1) and gut-specific (AjAPN4) isoforms in this moth. The expression of both the isoforms steadily increased during the larval development. Hormonal studies indicated regulation of the APN genes by the morphogenetic hormones, 20-hydroxyecdyone and juvenile hormone. Further, in vitro ligand-blotting studies demonstrated binding of Cry toxins to APNs in Malpighian tubule and salivary gland indicating their potential as alternate targets.

Effects of 90-day feeding of transgenic Bt rice TT51 on the reproductive system in male rats

Rice is a staple food crop; however, the threat of pests leads to a serious decline in its output and quality. The CryAb/CryAc gene, encodes a synthetic fusion Bacillus thuringiensis (Bt) crystal protein, was introduced into rice MingHui63 to produce insect-resistant rice TT51. This study was undertaken to investigate potential unintended effects of TT51 on the reproductive system in male rats. Male rats were treated with diets containing 60% of either TT51 or MingHui63 by weight, nutritionally balanced to an AIN93G diet, for 90days. An additional negative control group of rats were fed with a rice-based AIN93G diet. Body weights, food intake, hematology, serum chemistry, serum hormone levels, sperm parameters and relative organ/body weights were measured, and gross as well as microscopic pathology were examined. No diet-related significant differences in the values of response variables were observed between rats that were fed with diet containing transgenic TT51, MingHui63 and the control in this 90-day feeding study. In addition, necropsy and histopathology examination indicated no treatment-related changes. The results from the present study indicated that TT51 does not appear to exert any effect on the reproductive system in male rats compared with MingHui63 or the control.

Bacillus thuringiensis-derived Cry5B Has Potent Anthelmintic Activity against Ascaris suum

Ascaris suum and Ascaris lumbricoides are two closely related geo-helminth parasites that ubiquitously infect pigs and humans, respectively. Ascaris suum infection in pigs is considered a good model for A. lumbricoides infection in humans because of a similar biology and tissue migration to the intestines. Ascaris lumbricoides infections in children are associated with malnutrition, growth and cognitive stunting, immune defects, and, in extreme cases, life-threatening blockage of the digestive tract and aberrant migration into the bile duct and peritoneum. Similar effects can be seen with A. suum infections in pigs related to poor feed efficiency and performance. New strategies to control Ascaris infections are needed largely due to reduced treatment efficacies of current anthelmintics in the field, the threat of resistance development, and the general lack of new drug development for intestinal soil-transmitted helminths for humans and animals. Here we demonstrate for the first time that A. suum expresses the receptors for Bacillus thuringiensis crystal protein and novel anthelmintic Cry5B, which has been previously shown to intoxicate hookworms and which belongs to a class of proteins considered non-toxic to vertebrates. Cry5B is able to intoxicate A. suum larvae and adults and triggers the activation of the p38 mitogen-activated protein kinase pathway similar to that observed with other nematodes. Most importantly, two moderate doses of 20 mg/kg body weight (143 nM/kg) of Cry5B resulted in a near complete cure of intestinal A. suum infections in pigs. Taken together, these results demonstrate the excellent potential of Cry5B to treat Ascaris infections in pigs and in humans and for Cry5B to work effectively in the human gastrointestinal tract.

Activity of Bacillus thuringiensis cyt1Ba crystal protein against hymenopteran forest pests

A crystal–spore suspension of PS201T6 was toxic to larvae of Diprion similis (Hymenoptera: Diprionidae). Toxicity was at least in part attributable to the Cyt1Ba crystal protein, as demonstrated by bioassays of solubilized protein produced by Escherichia coli expressing PS201T6’s cyt1Ba gene. PS201T6 reduced survival and growth of D. similis in a 2-week field experiment. In laboratory bioassays, both toxin and parental strain affected Acantholyda erythrocephala (Pamphiliidae), Pikonema alaskensis (Tenthredinidae), and Neodiprion sertifer (Diprionidae), as well as spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae). Affecting insects across at least four orders (Diptera, Coleoptera, Hymenoptera, Lepidoptera), Cyt1Ba has the broadest insecticidal activity spectrum among Bacillus thuringiensis crystal proteins documented to date.

Variant cry1Ab entomocidal Bacillus thuringiensis toxin gene facilitates the recovery of an increased number of lepidopteran insect resistant independent rice transformants against yellow stem borer (Scirpophaga incertulus) inflicted damage

The primary technical constraint plant scientists face in generating insect resistant transgenic crops with insecticidal Bacillus thuringiensis (Bt) crystal protein (Cry) genes remains failing to generate sufficiently large numbers of effective resistant transgenic plant lines. One possible means to overcome this challenge is through deployment of a Cry toxin gene that contains high levels of insecticidal specific activity for target insect pests. In the present study, we tested this hypothesis using a natural variant of the Cry1Ab toxin under laboratory conditions that possessed increased insecticidal potency against the yellow stem borer (YSB, Scirpophaga incertulus), one of the most damaging rice insect pests. Following adoption of a stringent selection strategy for YSB resistant transgenic rice lines under field conditions, results showed recovery of a significantly higher number of YSB resistant independent transgenic plant lines with the variant cry1Ab gene relative to transgenic plant lines harbouring cry1Ab berliner gene. Structural homology modelling of the variant toxin peptide with the Cry1Aa toxin molecule, circular dichroism spectral analysis, and hydropathy plot analysis indicated that serine substitution by phenylalanine at amino acid position 223 of the Cry1Ab toxin molecule resulted in a changed role for α-helix 7 in domain I of Cry1Ab for enhanced toxicity.

Insecticidal activity of recombinant baculovirus co-expressing Bacillus thuringiensis crystal protein and Kunitz-type toxin isolated from the venom of bumblebee Bombus ignitus

To improve the insecticidal activity of Autographa californica nucleopolyhedrovirus (AcMNPV), using co-expression of Bacillus thuringiensis crystal protein and a Kunitz-type toxin isolated from bumblebee Bombus ignitus venom, a recombinant AcMNPV, ApPolh5-3006BiKTI, expressing Bi-KTI under the control of early promoter from Cotesia plutellae bracovirus (CpBV) was constructed. In this recombinant virus, B. thuringiensis cry1-5 crystal protein gene was introduced into the genome by the fusion of polyhedrin-cry1-5 under the control of polyhedrin gene promoter. RT-PCR analysis indicated that both Bi-KTI and polyhedrin-cry1-5 fusion protein were successfully expressed from the infected cells. In addition, SDS-PAGE revealed that polyhedrin-cry1-5 fusion protein expressed by recombinant viruses was occluded into the polyhedra. ApPolh5-3006BiKTI showed an improved insecticidal activity against larvae of Plutella xylostella and Spodoptera exigua. At low dosage rates, it was more effective against S. exigua than on P. xylostella, but more rapid insecticidal activity was shown in P. xylostella. These results strongly suggest that co-expression of Bt toxin and Kunitz-type toxins could be successfully applied to improve the insecticidal activity of baculoviruses.

Mechanistic and Single-Dose In Vivo Therapeutic Studies of Cry5B Anthelmintic Action against Hookworms

BackgroundHookworm infections are one of the most important parasitic infections of humans worldwide, considered by some second only to malaria in associated disease burden. Single-dose mass drug administration for soil-transmitted helminths, including hookworms, relies primarily on albendazole, which has variable efficacy. New and better hookworm therapies are urgently needed. Bacillus thuringiensis crystal protein Cry5B has potential as a novel anthelmintic and has been extensively studied in the roundworm Caenorhabditis elegans. Here, we ask whether single-dose Cry5B can provide therapy against a hookworm infection and whether C. elegans mechanism-of-action studies are relevant to hookworms.Methodology/Principal FindingsTo test whether the C. elegans invertebrate-specific glycolipid receptor for Cry5B is relevant in hookworms, we fed Ancylostoma ceylanicum hookworm adults Cry5B with and without galactose, an inhibitor of Cry5B-C. elegans glycolipid interactions. As with C. elegans, galactose inhibits Cry5B toxicity in A. ceylanicum. Furthermore, p38 mitogen-activated protein kinase (MAPK), which controls one of the most important Cry5B signal transduction responses in C. elegans, is functionally operational in hookworms. A. ceylanicum hookworms treated with Cry5B up-regulate p38 MAPK and knock down of p38 MAPK activity in hookworms results in hypersensitivity of A. ceylanicum adults to Cry5B attack. Single-dose Cry5B is able to reduce by >90% A. ceylanicum hookworm burdens from infected hamsters, in the process eliminating hookworm egg shedding in feces and protecting infected hamsters from blood loss. Anthelmintic activity is increased about 3-fold, eliminating >97% of the parasites with a single 3 mg dose (∼30 mg/kg), by incorporating a simple formulation to help prevent digestion in the acidic stomach of the host mammal.Conclusions/SignificanceThese studies advance the development of Cry5B protein as a potent, safe single-dose anthelmintic for hookworm therapy and make available the information of how Cry5B functions in C. elegans in order to study and improve Cry5B function against hookworms.

NeuroBactrus, a Novel, Highly Effective, and Environmentally Friendly Recombinant Baculovirus Insecticide

A novel recombinant baculovirus, NeuroBactrus, was constructed to develop an improved baculovirus insecticide with additional beneficial properties, such as a higher insecticidal activity and improved recovery, compared to wild-type baculovirus. For the construction of NeuroBactrus, the Bacillus thuringiensis crystal protein gene (here termed cry1-5) was introduced into the Autographa californica nucleopolyhedrovirus (AcMNPV) genome by fusion of the polyhedrin-cry1-5-polyhedrin genes under the control of the polyhedrin promoter. In the opposite direction, an insect-specific neurotoxin gene, AaIT, from Androctonus australis was introduced under the control of an early promoter from Cotesia plutellae bracovirus by fusion of a partial fragment of orf603. The polyhedrin-Cry1-5-polyhedrin fusion protein expressed by the NeuroBactrus was not only occluded into the polyhedra, but it was also activated by treatment with trypsin, resulting in an ∼65-kDa active toxin. In addition, quantitative PCR revealed that the neurotoxin was expressed from the early phase of infection. NeuroBactrus showed a high level of insecticidal activity against Plutella xylostella larvae and a significant reduction in the median lethal time against Spodoptera exigua larvae compared to those of wild-type AcMNPV. Rerecombinant mutants derived from NeuroBactrus in which AaIT and/or cry1-5 were deleted were generated by serial passages in vitro. Expression of the foreign proteins (B. thuringiensis toxin and AaIT) was continuously reduced during the serial passage of the NeuroBactrus. Moreover, polyhedra collected from S. exigua larvae infected with the serially passaged NeuroBactrus showed insecticidal activity similar to that of wild-type AcMNPV. These results suggested that NeuroBactrus could be recovered to wild-type AcMNPV through serial passaging.

Detection and characterisation of a Bacillus thuringiensis crystal protein with nematicidal activity against the pinewood nematode Bursaphelenchus xylophilus

Nematicidal Bacillus thuringiensis (Bt) strains were isolated from forests in Zhejiang, China for further characterisation. PCR analysis was performed with nine pairs of primers specific for cry1, cry2, cry3, cry4, cry5, cry6, cry9, cry11 and cry13 to characterise and classify cry gene groups from Bt isolates. The isolates from individual cry groups were tested for nematicidal activity against the pinewood nematode Bursaphelenchus xylophilus, which is implicated in pine wilt disease. PCR identified 14 different categories of cry gene combinations, indicating a large diversity of cry genes. The cry1 gene was by far the most abundant in Bt isolates and was found in 68% of samples. The Bt isolates zjfc85 and zjfc392 were from two distinct classes, but shared the same cry5 amplification profile and the same ~130 kDa protein; they had the highest nematicidal activity against pinewood nematode during the 48 h exposure tests, resulting in 90 and 59% mortality (9% of mortality under control conditions), respectively. The ~130 kDa Cry protein from isolate zjfc85 was purified and named as Cry5Ba3. Bioassay results indicated pinewood nematode was highly susceptible to Cry5Ba3 and exhibited profound growth abnormalities after exposure to Cry5Ba3. Our results are a novel finding and provide a potential strategy to manage pine wilt disease caused by B. xylophilus based on a nematicidal Bt.

Improvement of Crystal Solubility and Increasing Toxicity against Caenorhabditis elegans by Asparagine Substitution in Block 3 of Bacillus thuringiensis Crystal Protein Cry5Ba

The crystal proteins from Bacillus thuringiensis are widely used for their specific toxicity against insects and nematodes. The highly conserved sequence blocks play an important role in Cry protein stability and flexibility, the basis of toxicity. The block 3 in Cry5Ba subfamily has a shorter sequence (only 12 residues) and more asparagine residues than that of others which harbor about 48 residues but only one asparagine. Based on the theoretical structure model of Cry5Ba, all three asparagines in block 3 are closely located in the interface of putative three domains, implying their probable importance in structure and function. In this study, all three asparagines in Cry5Ba2 block 3 were individually substituted with alanine by site-directed mutagenesis. The wild-type and mutant proteins were overexpressed and crystallized in acrystalliferous B. thuringiensis strain BMB171. However, the crystals formed in one of the mutants, designated N586A, abnormally disappeared and dissolved into the culture supernatant once the sporulation cells lysed, whereas the Cry5Ba crystal and the other mutant crystals were stable. The mutant N586A crystal, isolated from sporulation cells by the ultrasonic process, was found to be easily dissolved at wide range of pH value (5.0 to 10.0). Moreover, the toxicity assays showed that the mutant N586A exhibited nearly 9-fold-higher activity against nematodes and damaged the host's intestine more efficiently than the native Cry5Ba2. These data support the presumption that the amide residue Asn586 at the interface of domains might adversely affect the protein flexibility, solubility and resultant toxicity of Cry5Ba.