Toxicity of Bacillus thuringiensis to parasitic and free-living life-stages of nematode parasites of livestock

The nematode (Ascaris suum) intestine is a location of synergistic anthelmintic effects of Cry5B and levamisole

A novel group of biocidal compounds are the Crystal 3D (Cry) and Cytolytic (Cyt) proteins produced by Bacillus thuringiensis (Bt). Some Bt Cry proteins have a selective nematocidal activity, with Cry5B being the most studied. Cry5B kills nematode parasites by binding selectively to membrane glycosphingolipids, then forming pores in the cell membranes of the intestine leading to damage. Cry5B selectively targets multiple species of nematodes from different clades and has no effect against mammalian hosts. Levamisole is a cholinergic anthelmintic that acts by selectively opening L-subtype nicotinic acetylcholine receptor ion-channels (L-AChRs) that have been found on muscles of nematodes. A synergistic nematocidal interaction between levamisole and Cry5B at the whole-worm level has been described previously, but the location, mechanism and time-course of this synergism is not known. In this study we follow the timeline of the effects of levamisole and Cry5B on the Ca2+ levels in enterocyte cells in the intestine of Ascaris suum using fluorescence imaging. The peak Ca2+ responses to levamisole were observed after approximately 10 minutes while the peak responses to activated Cry5B were observed after approximately 80 minutes. When levamisole and Cry5B were applied simultaneously, we observed that the responses to Cry5B were bigger and occurred sooner than when it was applied by itself. It is proposed that the synergism is due to the cytoplasmic Ca2+ overload that is induced by the combination of levamisole opening Ca2+ permeable L-subtype nAChRs and the Ca2+ permeable Cry5B toxin pores produced in the enterocyte plasma membranes. The effect of levamisole potentiates and speeds the actions of Cry5B that gives rise to bigger Ca2+ overloads that accelerates cell-death of the enterocytes.

The nematode (Ascaris suum) intestine is a location of synergistic anthelmintic effects of Cry5B and levamisole

A novel group of biocidal compounds are the Crystal 3D (Cry) and Cytolytic (Cyt) proteins produced by Bacillus thuringiensis (Bt). Some Bt Cry proteins have a selective nematocidal activity, with Cry5B being the most studied. Cry5B kills nematode parasites by binding selectively to membrane glycosphingolipids, then forming pores in the cell membranes of the intestine leading to damage. Cry5B selectively targets multiple species of nematodes from different clades and has no effect against mammalian hosts. Levamisole is a cholinomimetic anthelmintic that acts by selectively opening L-subtype nicotinic acetylcholine receptor ion-channels (L-AChRs) that have been found on muscles of nematodes. A synergistic nematocidal interaction between levamisole and Cry5B has been described previously, but the location, mechanism and time-course of this synergism is not known. In this study we follow the timeline of the effects of levamisole and Cry5B on the Ca2+ levels in enterocyte cells from the intestine of Ascaris suum using fluorescence imaging. The peak Ca2+ responses to levamisole were observed after approximately 10 minutes while the peak responses to activated Cry5B were observed after approximately 80 minutes. When levamisole and Cry5B were applied simultaneously, we observed that the responses to Cry5B were bigger and occurred sooner than when it was applied by itself. It is proposed that there is an irreversible cytoplasmic Ca2+ overload that leads to necrotic cell-death in the enterocyte that is induced by levamisole opening Ca2+ permeable L-subtype nAChRs and the development of Ca2+ permeable Cry5B toxin pores in enterocyte plasma membranes. The effects of levamisole potentiate and speed the actions of Cry5B.

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.

Opposite Sides of Pantoea agglomerans and Its Associated Commercial Outlook

Multifaceted microorganisms such as the bacterium Pantoea colonize a wide range of habitats and can exhibit both beneficial and harmful behaviors, which provide new insights into microbial ecology. In the agricultural context, several strains of Pantoea spp. can promote plant growth through direct or indirect mechanisms. Members of this genus contribute to plant growth mainly by increasing the supply of nitrogen, solubilizing ammonia and inorganic phosphate, and producing phytohormones (e.g., auxins). Several other studies have shown the potential of strains of Pantoea spp. to induce systemic resistance and protection against pests and pathogenic microorganisms in cultivated plants. Strains of the species Pantoea agglomerans deserve attention as a pest and phytopathogen control agent. Several of them also possess a biotechnological potential for therapeutic purposes (e.g., immunomodulators) and are implicated in human infections. Thus, the differentiation between the harmful and beneficial strains of P. agglomerans is mandatory to apply this bacterium safely as a biofertilizer or biocontroller. This review specifically evaluates the potential of the strain-associated features of P. agglomerans for bioprospecting and agricultural applications through its biological versatility as well as clarifying its potential animal and human health risks from a genomic point of view.

Bacillus thuringiensis toxins with nematocidal activity against the pinewood nematode Bursaphelenchus xylophilus

The pine wilt disease is caused by the pinewood nematode Bursaphelenchus xylophilus and it results in serious ecological and economic losses. Therefore, effective prevention and control methods for the pinewood nematode are urgently required. Bacillus thuringiensis (Bt), a widely used microbial insecticide, produces toxins that are toxic to several species of parasitic nematodes, however, its effects on B. xylophilus have not been determined. In this study, Cry5Ba3, App6Aa2, Cry12Aa1, Cry13Aa1, Cry14Aa1, Cry21Aa3, Cry21Fa1, Xpp55Aa1, and Cyt8Aa1 toxins' nematocidal activity against B. xylophilus was evaluated, six toxins with high toxicity were identified: App6Aa2 (LC₅₀ = 49.71 μg/mL), Cry13Aa1 (LC₅₀ = 53.17 μg/mL), Cry12Aa1 (LC₅₀ = 58.88 μg/mL), Cry5Ba3 (LC₅₀ = 63.99 μg/mL), Xpp55Aa1 (LC₅₀ = 65.14 μg/mL), and Cyt8Aa1 (LC₅₀ = 96.50 μg/mL). The six toxins caused shrinkage and thinning of the intestinal cells, contraction of the intestine from the body wall, vacuolization, and degenerated appearance of the pinewood nematodes. The results of this study provide basic information to study the action mechanism of nematocidal toxins on the pinewood nematode and direction for the use of nematocidal toxins in the biological control of B. xylophilus.

Antinematode Activity of Abomasum Bacterial Culture Filtrates against Haemonchus contortus in Small Ruminants

Simple Summary

Haemonchus contortus is an important gastrointestinal nematode parasite of the tropical and sub-tropical regions that cause haemonchosis in small ruminants like goats and sheep. It causes low production, reduced growth and may cause death of the infected animals. Due to the resistance development and environmental issues, the use of anthelmintics can be replaced with biological control, which is an environment friendly alternative. In the present study, three bacteria viz; Comamonas testosteroni, C. jiangduensis and Pseudomonas weihenstephanesis showed significant effect on nematode mortality and egg hatch inhibition. It was also observed that the anthelmintic activity of these bacteria was dose dependent, where 100% bacterial metabolite concentration showed the highest activity. It is suggested that these bacteria may included in the integrated nematode management.

Abstract

Haemonchosis is a parasitic disease of small ruminants that adversely affects livestock production. Haemonchus contortus is one of the most prevalent nematode parasites that infect the abomasum of small ruminants. This parasite reduces milk production, overall growth and sometimes causes the death of the infected animals. The evaluation of the biocontrol potential of some abomasum bacterial isolates against H. contortus is investigated in this study. Out of which, three isolates—Comamonas testosteroni, Comamonas jiangduensis, Pseudomonas weihenstephanesis—show significant effect against the nematode L3, adult, and egg hatch inhibition assays. Various concentrations of metabolites from these bacteria are prepared and applied in different treatments compared with control. In the case of adult mortality assay, 50% metabolites of C. testosteroni and P. weihenstephanesis show 46% adult mortality, whereas C. jiangduensis shows 40% mortality. It is observed that decreasing the concentration of bacterial metabolite, lowers nematode mortality. The minimum nematode mortality rate is recorded at the lowest filtrates concentration of all the bacterial isolates. The same trend is observed in egg hatch inhibition assay, where the higher concentration of bacterial culture filtrates shows 100% inhibition of H. contortus egg. It is concluded that the effect of bacterial culture filtrates against H. contortus is dose-dependent for their activity against nematode L3, adult, and inhibition of egg hatchment.

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

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

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.

Nematicidal and ovicidal activity of Bacillus thuringiensis against the zoonotic nematode Ancylostoma caninum

Ancylostoma caninum is a gastrointestinal parasite that affect dogs and humans, considered a worldwide public health problem. The control of these parasitosis is increasingly difficult due to the development of multi-drug resistance. Bacillus thuringiensis is an insecticidal, spore forming bacterium, often species specific. The strain GP526 of B. thuringiensis has toxic effect on the cestode Dipylidium caninum and the trematode Centrocestus formosanus, both of them zoonotic parasites. The high degrees of specificity and environment safe make B. thuringiensis suitable for use against pathogen parasites, especially those resistant to synthetic chemical insecticides. The objective of the current work was to evaluate the in vitro effect of B. thuringiensis on Ancylostoma caninum. Spore-crystal mixture of the strains was co-incubated with 120 adult nematodes (males, non-pregnant females and pregnant females) or with 4800 eggs. GP526 showed a nematicidal effect with an LT₅₀ of 35.8 h and an LC₅₀ of 60 μg/ml. It also showed an ovicidal effect with an LC₅₀ of 94.9 μg/ml. Histological analyses showed detachment of the cuticle and of the uterus in adult females, and vacuolization with destruction of the eggs. The effects of GP526 strain were comparable to those of albendazole, allowing us to propose GP526 for A. caninum control, in both, the adult stage at a gastrointestinal level, and in egg stage in the environment. In addition, GP526 can be proposed as a potential broad spectrum antiparasitic drug.

The Cytocidal Spectrum of Bacillus thuringiensis Toxins: From Insects to Human Cancer Cells

Bacillus thuringiensis (Bt) is a ubiquitous bacterium in soils, insect cadavers, phylloplane, water, and stored grain, that produces several proteins, each one toxic to different biological targets such as insects, nematodes, mites, protozoa, and mammalian cells. Most Bt toxins identify their particular target through the recognition of specific cell membrane receptors. Cry proteins are the best-known toxins from Bt and a great amount of research has been published. Cry are cytotoxic to insect larvae that affect important crops recognizing specific cell membrane receptors such as cadherin, aminopeptidase-N, and alkaline phosphatase. Furthermore, some Cry toxins such as Cry4A, Cry4B, and Cry11A act synergistically with Cyt toxins against dipteran larvae vectors of human disease. Research developed with Cry proteins revealed that these toxins also could kill human cancer cells through the interaction with specific receptors. Parasporins are a small group of patented toxins that may or may not have insecticidal activity. These proteins could kill a wide variety of mammalian cancer cells by recognizing specific membrane receptors, just like Cry toxins do. Surface layer proteins (SLP), unlike the other proteins produced by Bt, are also produced by most bacteria and archaebacteria. It was recently demonstrated that SLP produced by Bt could interact with membrane receptors of insect and human cancer cells to kill them. Cyt toxins have a structure that is mostly unrelated to Cry toxins; thereby, other mechanisms of action have been reported to them. These toxins affect mainly mosquitoes that are vectors of human diseases like Anopheles spp (malaria), Aedes spp (dengue, zika, and chikungunya), and Culex spp (Nile fever and Rift Valley fever), respectively. In addition to the Cry, Cyt, and parasporins toxins produced during spore formation as inclusion bodies, Bt strains also produce Vip (Vegetative insecticidal toxins) and Sip (Secreted insecticidal proteins) toxins with insecticidal activity during their vegetative growth phase.

Bacillus thuringiensis strains from Western Ghats of India possess nematocidal property against Haemonchus contortus larvae of goats

Nematocidal properties of spore crystal mixtures of six Bacillus thuringiensis (Bt) strains (KAU 49, 50, 52, 61, 99 and 424) collected from Western Ghats, a biodiversity hot spot of India, were analysed against Haemonchus contortus larvae isolated from goats. One dose nematocidal assay dose response to lyophilised spore-crystal mixtures (SCM) of the six Bt strains were determined by adding 200 μg/mL of each SCMs to culture plate wells containing aqueous suspension of H. contortus larvae. Out of the strains screened, KAU 50 and 424 were found to possess nematocidal properties. Maximum nematocidal properties were exhibited 7 days post-inoculation of the lyophilised SCMs. The 50 per cent lethal concentrations deduced by log probit analysis for KAU 50 was found to be 130.59 μg/mL, whereas that of KAU 424 was found to be 144.536 μg/mL at 95 per cent confidence level. This is the first report on the nematocidal propery of Bt strains against Haemonchus contortus larvae isolated from goats. Further studies are needed for identification and characterisation of the toxin.

Health and nutrition in sheep receiving Bacillus thuringiensis

Performance, nutrient apparent digestibility, ruminal parameters, enteric methane (CH4) emission and blood parameters were studied in sheep receiving spores of Bacillus thuringiensis (Bt) in their diet. Twenty Santa Inês lambs (10 castrated males and 10 females) with 18.0 ± 3.50 kg initial bodyweight (BW) and 3 months of age were maintained in individual stalls in a completely randomised design. They were divided into two groups with five males and five females each (Bt 2036 group (n = 10) and control group (n = 10)). The animals of the Bt 2036 group received daily 2.5 × 106 spores of Bt 2036/kg BW and control animals received a placebo. The diet consisted of Tifton-85 (Cynodon spp.) hay ad libitum and 300 g/animal.day of concentrate mixture, which was adjusted according to growth requirements. During 53 days, animal performance was evaluated, with feed intake measured three times per week and lambs weighed fortnightly. Blood samples were taken every 15 days to evaluate hematological and biochemical parameters. Rumen fermentation was investigated in three stages (start, middle and end of the experimental period) using parameters such as pH, ammoniacal nitrogen, short chain fatty acids, and populations of Fibrobacter succinogenes, Ruminococcus flavefaciens, anaerobic fungi, methanogenic archaea and protozoa. At the end of the performance experiment, 18 lambs (Bt 2036 (n = 9), control (n = 9)) were selected for a digestibility trial, and placed in metabolic cages to estimate apparent nutrient digestibility, nitrogen balance and microbial protein synthesis. Ten male (Bt 2036 (n = 5), control (n = 5)) lambs were used to evaluate CH4 production using the hexafluoride tracer technique. There was no effect (P > 0.05) of Bt 2036 on any of the evaluated parameters. The daily addition of 2.5 × 106 spores/kg BW of Bt 2036 in the ruminant diet did not cause any negative effects on hematological traits or animal poisoning, nor did it interfere with fermentation by rumen microorganisms, apparent digestibility of nutrients or animal performance.

Suppressing a plant-parasitic nematode with fungivorous behavior by fungal transformation of a Bt cry gene

BACKGROUND

Pine wilt disease, caused by the pinewood nematode Bursaphelenchus xylophilus (PWN), is an important destructive disease of pine forests worldwide. In addition to behaving as a plant-parasitic nematode that feeds on epithelial cells of pines, this pest relies on fungal associates for completing its life cycle inside pine trees. Manipulating microbial symbionts to block pest transmission has exhibited an exciting prospect in recent years; however, transforming the fungal mutualists to toxin delivery agents for suppressing PWN growth has received little attention.

RESULTS

In the present study, a nematicidal gene cry5Ba3, originally from a soil Bacillus thuringiensis (Bt) strain, was codon-preferred as cry5Ba3Φ and integrated into the genome of a fungus eaten by PWN, Botrytis cinerea, using Agrobacterium tumefaciens-mediated transformation. Supplementing wild-type B. cinerea extract with that from the cry5Ba3Φ transformant significantly suppressed PWN growth; moreover, the nematodes lost fitness significantly when feeding on the mycelia of the cry5Ba3Φ transformant. N-terminal deletion of Cry5Ba3Φ protein weakened the nematicidal activity more dramatically than did the C-terminal deletion, indicating that domain I (endotoxin-N) plays a more important role in its nematicidal function than domain III (endotoxin-C), which is similar to certain insecticidal Cry proteins.

CONCLUSIONS

Transformation of Bt nematicidal cry genes in fungi can alter the fungivorous performance of B. xylophilus and reduce nematode fitness. This finding provides a new prospect of developing strategies for breaking the life cycle of this pest in pines and controlling pine wilt disease.

Bacillus thuringiensis Cry5B protein as a new pan-hookworm cure

Hookworms are intestinal nematode parasites that infect nearly half a billion people and are globally one of the most important contributors to iron-deficiency anemia. These parasites have significant impacts in developing children, pregnant women and working adults. Of all the soil-transmitted helminths or nematodes (STNs), hookworms are by far the most important, with disease burdens conservatively estimated at four million DALYs (Disability-Adjusted Life Years) and with productivity losses of up to US$139 billion annually. To date, mainly one drug, albendazole is used for hookworm therapy in mass drug administration, which has on average ∼80% cure rate that is lower (<40%) in some places. Given the massive numbers of people needing treatment, the threat of parasite resistance, and the inadequacy of current treatments, new and better cures against hookworms are urgently needed. Cry5B, a pore-forming protein produced by the soil bacterium Bacillus thuringiensis (Bt) has demonstrated good efficacy against Ancylostoma ceylanicum hookworm infections in hamsters. Here we broaden studies of Cry5B to include tests against infections of Ancylostoma caninum hookworms in dogs and against infections of the dominant human hookworm, Necator americanus, in hamsters. We show that Cry5B is highly effective against all hookworm parasites tested in all models. Neutralization of stomach acid improves Cry5B efficacy, which will aid in practical application of Cry5B significantly. Importantly, we also demonstrate that the anti-nematode therapeutic efficacy of Cry5B is independent of the host immune system and is not itself negated by repeated dosing. This study indicates that Bt Cry5B is a pan-hookworm anthelmintic with excellent properties for use in humans and other animals.

Nematicidal Activity of Cry1Ea11 from Bacillus thuringiensis BRC-XQ12 Against the Pine Wood Nematode (Bursaphelenchus xylophilus)

The nematicidal activity of 92 Bacillus thuringiensis strains against the pine wood nematode Bursaphelenchus xylophilus, one of the world's top 10 plant-parasitic nematodes, was determined. The insecticidal crystal proteins (ICPs) from Bacillus thuringiensis BRC-XQ12 were the most toxic to Bursaphelenchus xylophilus, with a lethal concentration 50 (LC₅₀) of 32.13 μg/ml. Because the ICPs expressed by Bacillus thuringiensis BRC-XQ12 were closest to Cry1Ea6 and B. thuringiensis BRC-XQ12 contained four kinds of cry1 subgenes (cry1Aa, cry1Cb, cry1Ea, and cry1Ia), Cry1Ea was most likely to be the key active component against the nematode. The 3,516-bp cry1Ea11 gene from BRC-XQ12, as designated by the B. thuringiensis δ-endotoxin nomenclature committee, was expressed in Escherichia coli. Purified Cry1Ea11 showed an LC₅₀ of 32.53 and 23.23 μg/ml at 24 and 48 h, with corresponding virulence equations of Y = 32.15X + 1.38 (R² = 0.9951) and Y = 34.29X + 3.16 (R² = 0.9792), respectively. In order to detect the pathway of B. thuringiensis Cry1Ea11 into Bursaphelenchus xylophilus, the nematode was fed with NHS-rhodamine-labeled GST-Cry1Ea11. The results of confocal laser-scanning microscopy showed that the 159-kDa GST-Cry1Ea11 could be detected in the stylet and the esophageal lumen of the pine wood nematode, indicating that GST-Cry1Ea11 could enter into the nematode through the stylet. As far as we know, no Cry1 proteins have been shown to have activity against plant-parasitic nematodes before. These results demonstrate that Cry1Ea11 is a promising nematicidal protein for controlling pine wilt disease rendered by B. xylophilus, further dramatically broadening the spectrum of Bacillus thuringiensis ICPs.

Bacillus thuringiensis: a successful insecticide with new environmental features and tidings

Bacillus thuringiensis (Bt) is known as the most successful microbial insecticide against different orders of insect pests in agriculture and medicine. Moreover, Bt toxin genes also have been efficiently used to enhance resistance to insect pests in genetically modified crops. In light of the scientific advantages of new molecular biology technologies, recently, some other new potentials of Bt have been explored. These new environmental features include the toxicity against nematodes, mites, and ticks, antagonistic effects against plant and animal pathogenic bacteria and fungi, plant growth-promoting activities (PGPR), bioremediation of different heavy metals and other pollutants, biosynthesis of metal nanoparticles, production of polyhydroxyalkanoate biopolymer, and anticancer activities (due to parasporins). This review comprehensively describes recent advances in the Bt whole-genome studies, the last updated known Bt toxins and their functions, and application of cry genes in plant genetic engineering. Moreover, the review thoroughly describes the new features of Bt which make it a suitable cell factory that might be used for production of different novel valuable bioproducts.

Larvicidal activity of Bacillus circulans against the gastrointestinal nematode Haemonchus contortus in sheep

Efficient control of gastrointestinal parasites is necessary in sheep breeding. However, the available chemically based anthelmintics are becoming less effective due to the development of parasite resistance. An alternative to this problem is biological control. In the present study, we tested the larvicidal effect of Bacillus circulans by administering a spore suspension (2 × 109 colony forming units/ml) orally to lambs naturally infected with Haemonchus contortus. The number of faecal larvae was quantified daily and a significant reduction (~87%, P< 0.05) of larval development was observed after administration of B. circulans. Using a transformed B. circulans with green fluorescent protein, we were able to detect B. circulans in the faeces at 4 h post-administration and 72 h after cessation of its administration. These results suggest the use of B. circulans as a promising biological alternative for parasite control.

Larvicidal activity of Bacillus thuringiensis var. israelensis Cry11Aa toxin against Haemonchus contortus

Effective control of gastrointestinal parasites is necessary in sheep production. The development of anthelmintics resistance is causing the available chemically based anthelmintics to become less effective. Biological control strategies present an alternative to this problem. In the current study, we tested the larvicidal effects of Bacillus thuringiensis var. israelensis Cry11Aa toxin against Haemonchus contortus larvae. Bacterial suspensions [2 × 108 colony-forming units (CFU) g-1 of the feces] of B. thuringiensis var. israelensis and recombinant Escherichia coli expressing Cry11Aa toxin were added to naturally H. contortus egg-contaminated feces. The larvae were quantified, and significant reductions of 62 and 81% (P < 0·001) were, respectively observed, compared with the control group. A 30 mL bacterial suspension (1 × 108 CFU mL-1) of B. thuringiensis var. israelensis and recombinant E. coli expressing Cry11Aa toxin were then orally administered to lambs naturally infected with H. contortus. Twelve hours after administration, feces were collected and submitted to coprocultures. Significant larvae reductions (P < 0·001) of 79 and 90% were observed respectively compared with the control group. The results suggest that the Cry11Aa toxin of B. thuringiensis var. israelensis is a promising new class of biological anthelmintics for treating sheep against H. contortus.

Haemonchus contortus: Applications in Drug Discovery

Haemonchus contortus is an important pathogen of small ruminants and is therefore a crucially important target for anthelmintic chemotherapy. Its large size and fecundity have been exploited for the development of in vitro screens for anthelmintic discovery that employ larval and adult stages in several formats. The ability of the parasite to develop to the young adult stage in Mongolian jirds (Meriones unguiculatus) provides a useful small animal model that can be used to screen compounds prior to their evaluation in infected sheep. This chapter summarizes the use of H. contortus for anthelmintic discovery, offers a perspective on current strategies in this area and suggests research challenges that could lead to improvements in the anthelmintic discovery process.

A two-domain protein triggers heat shock pathway and necrosis pathway both in model plant and nematode

The entomopathogen Bacillus thuringiensis is equipped with multiple virulent factors. The genome sequence of B. thuringiensis YBT1520 revealed the presence of a two-domain protein named Nel which is composed of a necrosis-inducing phytophthora protein 1-like domain found in phytopathogens and a ricin B-like lectin domain. The merging of two distantly related domains is relatively rare. Nel induced necrosis and pathogen-triggered immunity (PTI) on model plants. The Nel also exhibited inhibition activity to nematode. Microscopic observation showed that the toxicity of Nel to nematodes targets the intestine. Quantitative proteomics revealed that Nel stimulated the host defence. The Nel thus possesses dual roles, as both toxin and elicitor. Remarkably, the Nel protein triggered a similar response, induction of the heat shock pathway and the necrosis pathway, in both model plants and nematodes. The unusual ability of Nel to function across kingdom suggests a highly conserved mechanism in eukaryotes that predates the divergence of plants and animal. It is also speculated that the two-domain protein is the result of horizontal gene transfer (HGT) between phytopathogens and entomopathogens. Our results provide an example that HGT occurs between members of different species or even genera with lower frequency are particularly important for evolution of new bacterial pathogen lineages with new virulence. Bacillus thuringiensis occupies the same ecological niches, plant and soil, as phytopathogens, providing the opportunity for gene exchange.

Control of Diatraea saccharalis by the endophytic Pantoea agglomerans 33.1 expressing cry1Ac7

Despite the fact that Bacillus thuringiensis (Bt) is found in more than 90 % of the products used against insects, it has some difficulty reaching the internal regions where the larvae feed. To solve this problem, many genetically modified microorganisms that colonize the same pests have been developed. Thus, the endophytic bacterium Pantoea agglomerans (33.1), which has been recently described as a promising sugarcane growth promoter, was genetically modified with the pJTT vector (which carries the gene cry1Ac7) to control the sugarcane borer, Diatraea saccharalis. Firstly, the bioassays for D. saccharalis control by 33.1:pJTT were conducted with an artificial diet. A new in vivo methodology was also developed, which confirmed the partial control of larvae by 33.1:pJTT. The 33.1:pJTT strain was inoculated into sugarcane stalks containing the D. saccharalis larvae. In the sugarcane stalks, 33.1:pJTT was able to increase the mortality of D. saccharalis larvae, impair larval development and decrease larval weight. Sugarcane seedlings were inoculated with 33.1:pJTT, and re-isolation confirmed the capacity of 33.1:pJTT to continuously colonize the sugarcane. These results prove that P. agglomerans (33.1), a sugarcane growth promoter, can be improved by expressing the Cry protein, and the resulting strain is able to control the sugarcane borer.

The highly modified microcin peptide plantazolicin is associated with nematicidal activity of Bacillus amyloliquefaciens FZB42

Bacillus amyloliquefaciens FZB42 has been shown to stimulate plant growth and to suppress the growth of plant pathogenic organisms including nematodes. However, the mechanism underlying its effect against nematodes remains unknown. In this study, we screened a random mutant library of B. amyloliquefaciens FZB42 generated by the mariner transposon TnYLB-1 and identified a mutant strain F5 with attenuated nematicidal activity. Reversible polymerase chain reaction revealed that three candidate genes RAMB_007470, yhdY, and prkA that were disrupted by the transposon in strain F5 potentially contributed to its decreased nematicidal activity. Bioassay of mutants impaired in the three candidate genes demonstrated that directed deletion of gene RBAM_007470 resulted in loss of nematicidal activity comparable with that of the F5 triple mutant. RBAM_007470 has been reported as being involved in biosynthesis of plantazolicin, a thiazole/oxazole-modified microcin with hitherto unknown function. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) analyses of surface extracts revealed that plantazolicin bearing a molecular weight of 1,354 Da was present in wild-type B. amyloliquefaciens FZB42, but absent in the ΔRABM_007470 mutant. Furthermore, bioassay of the organic extract containing plantazolicin also showed a moderate nematicidal activity. We conclude that a novel gene RBAM_007470 and its related metabolite are involved in the antagonistic effect exerted by B. amyloliquefaciens FZB42 against nematodes.

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.

Ascaris suum is an intestinal parasitic nematode of pigs that is very closely related to Ascaris lumbricoides, a major intestinal parasitic nematode of humans that infects more than one billion people worldwide. Because of reduced efficacy and the threat of resistance to the current small set of approved drugs to treat Ascaris infections, new treatments are needed. Here we test against A. suum infections the effectiveness of Cry5B, a nematode-killing protein made by the natural soil bacterium Bacillus thuringiensis and representing a promising new class of anthelmintics. We demonstrate for the first time that A. suum possesses the receptors to bind Cry5B and that Cry5B can kill A. suum larvae and adults in culture. Most importantly, we demonstrate that oral administration of Cry5B to pigs infected with A. suum larvae results in a near complete elimination of the infection. Given the similarities between A. suum and A. lumbricoides and the similarity between the pig and human gastrointestinal tracts, our data indicate that Cry5B has excellent potential to treat Ascaris infections in veterinary animals and in humans.

Cross-order and cross-phylum activity of Bacillus thuringiensis pesticidal proteins

The increasing number of Bacillus thuringiensis proteins with pesticidal activities across orders and phyla raises the question how widespread cross-activities are and if they are of sufficient biological significance to have implications for ecological safety of those proteins in pest control applications. Cross-activity is reported for 27 proteins and 69 taxa and is substantiated by reasonable evidence (mortality estimates) in 19 cases involving 45 taxa. Cross-activities occur in 13 primary rank families across three classes of pesticidal proteins (Cry, Cyt and Vip), and comprise 13 proteins affecting species across two orders, five proteins affecting three orders and one protein affecting four orders, all within the class Insecta. Cross-activity was quantified (LC50 estimates) for 16 proteins and 25 taxa. Compared to toxicity ranges established for Diptera-, Coleoptera-, Lepidoptera- and Nematoda-active proteins, 13 cross-activities are in the low-toxicity range (10-1000μg/ml), 12 in the medium - (0.10-10μg/ml) and two in the high-toxicity range (0.01-0.10μg/ml). Although cross-activities need to be viewed with caution until they are confirmed through independent testing, current evidence suggests that cross-activity of B. thuringiensis pesticidal proteins needs to be taken into consideration when designing and approving their use in pest control applications.

In vitro ovicidal and cestocidal effects of toxins from Bacillus thuringiensis on the canine and human parasite Dipylidium caninum

Bacillus thuringiensis is a gram-positive soil-dwelling bacterium that is commonly used as a biological pesticide. This bacterium may also be used for biological control of helminth parasites in domestic animals. In this study, we evaluated the possible ovicidal and cestocidal effects of a total protein extract of B. thuringiensis native strains on the zoonotic cestode parasite of dogs, Dipylidium caninum (D. caninum). Dose and time response curves were determined by coincubating B. thuringiensis proteins at concentration ranging from 100 to 1000 μ g/mL along with 4000 egg capsules of D. caninum. Egg viability was evaluated using the trypan blue exclusion test. The lethal concentration of toxins on eggs was 600 μ g/ml, and the best incubation time to produce this effect was 3 h. In the adult stage, the motility and the thickness of the tegument were used as indicators of damage. The motility was inhibited by 100% after 8 hours of culture compared to the control group, while the thickness of the cestode was reduced by 34%. Conclusively, proteins of the strain GP526 of B. thuringiensis directly act upon D. caninum showing ovicidal and cestocidal effects. Thus, B. thuringiensis is proposed as a potential biological control agent against this zoonosis.

Bacillus sphaericus in the adults of Culex quinquefasciatus mosquitoes emerged from treated larvae and its effect on development of the filarial parasite, Wuchereria bancrofti

Bacillus sphaericus is a bio-control agent effective against Culex quinquefasciatus, the vector of bancroftian filariasis. Apart from its larvicidal effect, there are reports of reduced infection of filarial parasites in mosquitoes exposed to it. In the present study, adults of Cx. quinquefasciatus emerged from B. sphaericus treated larvae were fed on blood samples positive for microfilariae of Wuchereria bancrofti and examined at various time intervals to assess the infection level. The rate of infection was reduced from 95% on day 1 post-feeding to 75% on day 13, when fed with blood sample containing 41 mf/20 μl. The mean parasite burden was also reduced from 4.9 per mosquito on day 1 to 2.15 on day 13. When fed with another sample (30 mf/20 μl), the infection was reduced from 100% on day 1 to 80% on day 13. Reduction in parasite burden was 4.0 to 1.75. Abnormally developed second-stage larvae of the parasite were seen in treated mosquitoes. Thus, the results indicated adverse effect of B. sphaericus treatment on infection and development of the filarial parasite in mosquitoes. The possible reason for the parasite regulation was studied through the assessment of the carryover of the bacterium as well as its toxins to the surviving mosquitoes. The presence of B. sphaericus was determined through plating of homogenate of survived mosquitoes on NYSM agar. Toxic protein was detected through immunoblotting. The bacterium as well as its 41.9-kDa toxic protein was found to be transmitted from larvae to adults and affected the parasite development, directly by the toxin or indirectly by eliciting humoral immune response of the mosquito.

Target-based and whole-worm screening approaches to anthelmintic discovery

Experimental approaches for identifying new anthelmintics include target-based and whole-worm screening methods. The former involves basic research into characterising and validating new targets, mostly proteins, followed by identification of inhibitors or agonists through the use of target-based screening assays and/or in silico drug design. The latter experimental approach uses whole-worm assays to identify anthelmintic agents with unknown modes of action, or where the primary interest lies in whether analogues are able to kill (or disable) worms rather than in measuring their direct impact on their likely target. This paper focuses initially on the intestine and external layers of nematodes as potential drug targets. Specific anthelmintic agents targeting either tissue are discussed to illustrate the impact of disruption to these structures. In both cases, the activity of these agents against insects was known, and activity against nematodes was identified using whole worm screening assays. Recent literature identifying ecdysone signalling pathway receptors in nematodes is then used to provide an example of basic research into a specific target that may lead to the development of high-throughput target-based drug screening assays. Finally, the role of whole-worm screening approaches versus target-based screening is discussed briefly.

A subset of naturally isolated Bacillus strains show extreme virulence to the free-living nematodes Caenorhabditis elegans and Pristionchus pacificus

The main food source of free-living nematodes in the soil environment is bacteria, which can affect nematode development, fecundity and survival. In order to occupy a reliable source of bacterial food, some nematodes have formed specific relationships with an array of invertebrate hosts (where bacteria proliferate once the hosts dies), thus forming a tritrophic system of nematode, bacteria and insect or other invertebrates. We isolated 768 Bacillus strains from soil (from Germany and the UK), horse dung and dung beetles and fed them to the genetically tractable free-living nematodes Caenorhabditis elegans and Pristionchus pacificus to isolate nematocidal strains. While C. elegans is a bacteriovorous soil nematode, P. pacificus is an omnivorous worm that is often found in association with scarab beetles. We found 20 Bacillus strains (consisting of B. cereus, B. weihenstephanensis, B. mycoides and Bacillus sp.) that were pathogenic to C. elegans and P. pacificus causing 70% to 100% mortality over 5 days and significantly affect development and brood size. The most pathogenic strains are three B. cereus-like strains isolated from dung beetles, which exhibit extreme virulence to C. elegans in less than 24 h, but P. pacificus remains resistant. C. elegans Bre mutants were also highly susceptible to the B. cereus-like strains indicating that their toxins use a different virulence mechanism than B. thuringiensis Cry 5B toxin. Also, mutations in the daf-2/daf-16 insulin signaling pathway do not rescue survival. We profiled the toxin genes (bcet, nhe complex, hbl complex, pcpl, sph, cytK, piplc, hly2, hly3, entFM and entS) of these three B. cereus-like strains and showed presence of most toxin genes but absence of the hbl complex. Taken together, this study shows that the majority of naturally isolated Bacillus from soil, horse dung and Geotrupes beetles are benign to both C. elegans and P. pacificus. Among 20 pathogenic strains with distinct virulence patterns against the two nematodes, we selected three B. cereus-like strains to investigate resistance and susceptibility immune responses in nematodes.

Novel Bacillus thuringiensis δ-endotoxin active against Locusta migratoria manilensis

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

Bacillus thuringiensis Cry5B protein is highly efficacious as a single-dose therapy against an intestinal roundworm infection in mice

Background

Intestinal parasitic nematode diseases are one of the great diseases of our time. Intestinal roundworm parasites, including hookworms, whipworms, and Ascaris, infect well over 1 billion people and cause significant morbidity, especially in children and pregnant women. To date, there is only one drug, albendazole, with adequate efficacy against these parasites to be used in mass drug administration, although tribendimidine may emerge as a second. Given the hundreds of millions of people to be treated, the threat of parasite resistance, and the inadequacy of current treatments, new anthelmintics are urgently needed. Bacillus thuringiensis (Bt) crystal (Cry) proteins are the most common used biologically produced insecticides in the world and are considered non-toxic to vertebrates.

Methods/Principal Findings

Here we study the ability of a nematicidal Cry protein, Cry5B, to effect a cure in mice of a chronic roundworm infection caused by the natural intestinal parasite, Heligmosomoides bakeri (formerly polygyrus). We show that Cry5B produced from either of two Bt strains can act as an anthelmintic in vivo when administered as a single dose, achieving a ∼98% reduction in parasite egg production and ∼70% reduction in worm burdens when delivered per os at ∼700 nmoles/kg (90–100 mg/kg). Furthermore, our data, combined with the findings of others, suggest that the relative efficacy of Cry5B is either comparable or superior to current anthelmintics. We also demonstrate that Cry5B is likely to be degraded quite rapidly in the stomach, suggesting that the actual dose reaching the parasites is very small.

Conclusions/Significance

This study indicates that Bt Cry proteins such as Cry5B have excellent anthelmintic properties in vivo and that proper formulation of the protein is likely to reveal a superior anthelmintic.

Intestinal parasitic nematode diseases infect over one billion people and cause significant disease burden in children (growth and cognitive stunting, malnutrition), in pregnant women, and via their dampening of the immune system in infected individuals. In over thirty years, no new classes of anti-roundworm drugs (anthelmintics) for treating humans have been developed. Because of limitations of the current drugs and the threat of parasite resistance, new anthelmintics are needed. The soil bacterium Bacillus thuringiensis (Bt) produces crystal (Cry) proteins that specifically target and kill insects and nematodes and is used around the world as a safe insecticide. Here we test the effects of the Bt Cry protein Cry5B on a chronic, natural intestinal roundworm infection in mice, namely the helminth parasite Heligmosomoides bakeri. We find that a single dose of Cry5B can eliminate 70% of the parasites and can almost completely block the ability of the parasites to produce progeny. Comparisons of Cry5B's efficacy with known anthelmintics suggest its activity is as good as or perhaps even better than those currently used. Furthermore, this protein is rapidly digested by simulated stomach juices, suggesting that protecting it from these juices would reveal a superior anthelmintic.

The theoretical three-dimensional structure of Bacillus thuringiensis Cry5Aa and its biological implications

Cry5Aa is a crystal protein produced by Bacillus thuringiensis serovar. damstadiensis during its stationary phase, this delta-endotoxin is active against nematodes and has great potential for nematodes control. The theoretical model of the three-dimensional structure of Cry5Aa was predicted by homology modeling on the structures of the Cry1Aa which is specific to Lepidopteran insects. The structure of the Cry5Aa resembles previously reported Cry toxin structures but shows the following distinctions. Cry5Aa has a long insertion in alpha2 of domain I. Some loops in the domain II and III of Cry5Aa are exposed to the solvent. In this work we give a brief description of our model and hypothesize the residues of the Cry5Aa that could be important in receptor recognition and pore formation. This model will be helpful for the design of mutagenesis experiments aimed to the improvement of toxicity, and lead to a deep understanding of the mechanism of action of nematicidal toxins.

Lethal activity of two Bacillus thuringiensis strains against Haemonchus contortus histotropic larvae

The in vitro lethal activity of two Bacillus thuringiensis strains (IB-16 and IB-61) against Haemonchus contortus histotropic fourth stage larvae (L(4)) was evaluated. Each B. thuringiensis strain was used as soluble proteins at different concentrations. In addition, the in vitro lethal dose (LD(50)) of each strain was determined against H. contortus L(4) at different times. Data were analyzed by ANOVA and Tukey tests. Less than 50% mortality was observed at 50 and 100 microg/mL during all bioassays. More than 50% mortality was observed at 200 microg/mL at 3 and 5 days after interaction with IB-16 and IB-61, respectively. A 100% mortality was observed with IB-16 on day 5. The LD(50) with IB-16 was 248 microg/mL on day 3, and IB-61 showed an LD(50) at 227 microg/mL on the day 5. Both toxins may have potential as biocontrol agents.

Molecular detection of nematicidal crystalliferousBacillus thuringiensisstrains of Iran and evaluation of their toxicity on free-living and plant-parasitic nematodes

The characterization of nematode-effective strains and cry genes in the Iranian Bacillus thuringiensis (Bt) collection (70 isolates) is presented. Characterization was based on PCR analysis using 12 specific primers for cry5, cry6, cry12, cry13, cry14, and cry21 genes encoding proteins active against nematodes, crystal morphology, and protein band patterns as well as their nematicidal activity on root-knot nematode ( Meloidogyne incognita ) and two free-living nematodes ( Chiloplacus tenuis and Acrobeloides enoplus ). PCR results with primers for these genes showed that 22 isolates (31.5%) contain a minimum of one nematode-active cry gene. Strains containing the cry6 gene were the most abundant and represent 22.8% of the isolates. Bt strains harboring cry14 genes were also abundant (14.2%). cry21 and cry5 genes were less abundant, found in 4.2% and 2.8% of the strains, respectively. In total, six different nematode-active cry gene profiles were detected in this collection. Four isolates did not show the expected PCR product size for cry5, cry6, and cry21 genes; they might contain potentially novel insecticidal crystal protein genes. Twenty-two Bt isolates containing nematode-active cry genes were selected for preliminary bioassays on M. incognita. Based on these bioassays, four isolates were selected for detailed bioassays. Isolates YD5 and KON4 at 2 × 108 CFU/mL concentrations showed 77% and 81% toxicity on M. incognita, respectively. The free-living nematodes C. tenuis and A. enoplus were more susceptible and the highest mortality was observed within 48 h of incubation at all of the concentrations tested. Maximum mortality was recorded for isolates SN1 and KON4 at 2 × 108 CFU/mL concentrations and resulted in 68% and 77% adults deaths of C. tenuis and 68% and 72% for A. enoplus, respectively. Our results showed that PCR is a useful technique for toxicity prediction of nematicidal Bt isolates.

The theoretical 3D structure of Bacillus thuringiensis Cry5Ba

Cry5Ba is a delta-endotoxin produced by Bacillus thuringiensis PS86A1 NRRL B-18900. It is active against nematodes and has great potential for nematode control. Here, we predict the first theoretical model of the three-dimensional (3D) structure of a Cry5Ba toxin by homology modeling on the structure of the Cry1Aa toxin, which is specific to Lepidopteran insects. Cry5Ba resembles the previously reported Cry1Aa toxin structure in that they share a common 3D structure with three domains, but there are some distinctions, with the main differences being located in the loops of domain I. Cry5Ba exhibits a changeable extending conformation structure, and this special structure may also be involved in pore-forming and specificity determination. A fuller understanding of the 3D structure will be helpful in the design of mutagenesis experiments aimed at improving toxicity, and lead to a deep understanding of the mechanism of action of nematicidal toxins.

A pair of adjacent genes, cry5Ad and orf2-5Ad, encode the typical N- and C-terminal regions of a Cry5Adelta-endotoxin as two separate proteins in Bacillus thuringiensis strain L366

A new DNA sequence cry5Ad/orf2-5Ad (GenBank accession number EF219060) was isolated from Bacillus thuringiensis strain L366. This DNA sequence contains two ORFs: cry5Ad (a previously unreported member of the cry5A gene family) and orf2-5Ad. cry5Ad is unique among cry5A genes in that it encodes only the N-terminal region of a typical Cry5Adelta-endotoxin. The cry5Ad sequence includes homology blocks 1-5, which are present in most B. thuringiensisdelta-endotoxins. The usual C-terminal region of a Cry5Adelta-endotoxin (including homology blocks 6-8) is encoded by orf2-5Ad. Both proteins encoded by cry5Ad and orf2-5Ad were found in IPTG-induced Escherichia coli, after a copy of cry5Ad/orf2-5Ad was cloned into the pQE32 expression vector and transformed into pREP4 E. coli cells. Both proteins were also found in parasporal crystal inclusions of B. thuringiensis L366. Sequencing of cDNA derived from transformed E. coli cells showed that the two ORFs are transcribed as a single mRNA. Extracts prepared from the recombinant E. coli expressing Cry5Ad and Orf2-5Ad were not toxic to nematode larvae (Haemonchus contortus), indicating that these two proteins are most likely not responsible for the nematocidal activity seen previously in the B. thuringiensis strain L366.

Identification of immuno-reactive proteins from a sheep gastrointestinal nematode, Trichostrongylus colubriformis, using two-dimensional electrophoresis and mass spectrometry

Gastrointestinal nematode infections of livestock animals are prevalent and costly problems worldwide. Currently, infections are controlled by anthelmintic chemicals but increasing drug resistance has prompted research interest to shift towards alternative methods of control such as vaccine development and selection of worm-resistant animals. The present study analyses proteins from Trichostrongylus colubriformis infective L3s that are recognised by IgG of immune sheep. Following protein separation via two-dimensional electrophoresis and Western blot probing with plasma from sheep resistant to T. colubriformis, mass spectrometry-based proteomic analyses were used to identify immuno-reactive protein spots. We were able to identify 28 immune targets, including aspartyl protease inhibitor, enolase, chaperone proteins, galectin, glycolytic enzymes, kinase, phosphatase and structural muscle proteins such as myosin, paramyosin, calponin and DIM-1. The data suggest that immune responses to T. colubriformis are dispersed over a relatively large number of parasite antigens, including several cytoplasmically expressed proteins. The results have new implications for understanding the molecular mechanisms that underpin host-parasite interaction during gastrointestinal nematode infections.

The requirement for early exposure of Haemonchus contortus larvae to Bacillus thuringiensis for effective inhibition of larval development

The potential for a nematocidal Bacillus thuringiensis (Bt) to target the free-living larval stages of Haemonchus contortus was examined using in vitro larval development and migration assays. Bt toxicity in larval development assays decreased as the time period between egg hatch and initial exposure to the Bt was increased; a time lag of 48 h resulted in a 350-fold increase in the IC(50) (from 2.6 ng/ml to 910 ng/ml). The effects on larval migration largely paralleled the effects on larval development, indicating that the larvae which reached the infective stage after exposure to Bt were generally as 'fit' as control worms in terms of migration ability. However, a comparison of the two assays also showed the presence of a level of Bt exposure which showed significantly more toxicity in migration assays than development assays, indicating that, in some cases, fully developed Bt-exposed larvae were less able to migrate than controls, and hence may be compromised in their ability to infect sheep. The rapid decrease in toxicity when exposure to the Bt is delayed highlights a significant issue concerning the use of Bt for control of the free-living larval stages of animal-parasitic nematodes. Targeting the larvae by delivering bacterial spores to the faeces through the host animal's digestive tract would require the spores to germinate upon defecation, grow through a vegetative phase, to then produce crystal toxin protein upon subsequent sporulation. This period of bacterial development will introduce a time lag between worm egg hatching and initial exposure of the larvae to the Bt, which, as demonstrated in the present study, may allow the worm larvae to develop to late larval stages which are relatively insensitive to the toxin.

Bacteria used in the biological control of plant-parasitic nematodes: populations, mechanisms of action, and future prospects

As a group of important natural enemies of nematode pests, nematophagous bacteria exhibit diverse modes of action: these include parasitizing; producing toxins, antibiotics, or enzymes; competing for nutrients; inducing systemic resistance of plants; and promoting plant health. They act synergistically on nematodes through the direct suppression of nematodes, promoting plant growth, and facilitating the rhizosphere colonization and activity of microbial antagonists. This review details the nematophagous bacteria known to date, including parasitic bacteria, opportunistic parasitic bacteria, rhizobacteria, Cry protein-forming bacteria, endophytic bacteria and symbiotic bacteria. We focus on recent research developments concerning their pathogenic mechanisms at the biochemical and molecular levels. Increased understanding of the molecular basis of the various pathogenic mechanisms of the nematophagous bacteria could potentially enhance their value as effective biological control agents. We also review a number of molecular biological approaches currently used in the study of bacterial pathogenesis in nematodes. We discuss their merits, limitations and potential uses.

Resistance to Bacillus thuringiensis toxin in Caenorhabditis elegans from loss of fucose

A mutation in the Caenorhabditis elegans bre-1 gene was isolated in a screen for Bacillus thuringiensis toxin-resistant (bre) mutants to the Cry5B crystal toxin made by B. thuringiensis. bre-1 mutant animals are different from the four other cloned bre mutants in that their level of resistance is noticeably lower. bre-1 animals also display a significantly reduced brood size at 25 degrees C. Here we cloned the bre-1 gene and characterized the bre-1 mutant phenotype. bre-1 encodes a protein with significant homology to a GDP-mannose 4,6-dehydratase, which catalyzes the first step in the biosynthesis of GDP-fucose from GDP-mannose. Injection of GDP-fucose but not fucose into C. elegans intestinal cells rescues bre-1 mutant phenotypes. Thus, C. elegans lacks a functional fucose salvage pathway. Furthermore, we demonstrate that bre-1 mutant animals are defective in production of fucosylated glycolipids and that bre-1 mutant animals make quantitatively reduced levels of glycolipid receptors for Cry5B. We finally show that bre-1 mutant animals, although viable, show a lack of fucosylated N- and O-glycans, based on mass spectrometric evidence. Thus, C. elegans can survive with little fucose and can develop resistance to crystal toxin by loss of a monosaccharide biosynthetic pathway.

A purified Bacillus thuringiensis crystal protein with therapeutic activity against the hookworm parasite Ancylostoma ceylanicum

Crystal (Cry) proteins produced by the soil bacterium Bacillus thuringiensis (Bt) are harmless to vertebrates, but they are highly toxic to insects and nematodes. Their value in controlling insects that destroy crops and transmit human diseases is well established. Although it has recently been demonstrated that a few individual Bt Cry proteins, such as Cry5B, are toxic to a wide range of free-living nematodes, the potential activity of purified Cry proteins against parasitic nematodes remains largely unknown. We report here studies aimed at characterizing in vitro and in vivo anthelminthic activities of purified recombinant Cry5B against the hookworm parasite Ancylostoma ceylanicum, a bloodfeeding gastrointestinal nematode for which humans are permissive hosts. By using in vitro larval development assays, Cry5B was found to be highly toxic to early stage hookworm larvae. Exposure of adult A. ceylanicum to Cry5B was also associated with significant toxicity, including a substantial reduction in egg excretion by adult female worms. To demonstrate therapeutic efficacy in vivo, hamsters infected with A. ceylanicum were treated with three daily oral doses of purified Cry5B, the benzimidazole anthelminthic mebendazole, or buffer. Compared with control (buffer-treated) animals, infected hamsters that received Cry5B showed statistically significant improvements in growth and blood hemoglobin levels as well as reduced worm burdens that were comparable to the mebendazole-treated animals. These data demonstrate that Cry5B is highly active in vitro and in vivo against a globally significant nematode parasite and that Cry5B warrants further clinical development for human and veterinary use.

RNA interference in Haemonchus contortus: Suppression of beta-tubulin gene expression in L3, L4 and adult worms in vitro

We have used RNAi to target two beta-tubulin genes in the parasitic stages of Haemonchus contortus in vitro. Soaking exsheathed-L3, L4 and adult worms in medium containing dsRNA resulted in a significant decrease (greater than 1000-fold in some cases) in the expression of the specific beta-tubulin transcript, as measured by quantitative PCR. During the initial 24h exposure to the dsRNA, the gene suppression effect was quite specific to the targeted gene. Six days after initial exposure to dsRNA, treated L3 worms were less able to migrate through a filter mesh, indicating decreased motility, and showed less development to the L4 stage than control larvae. The gene suppression effect occurs in exsheathed L3 larvae despite the fact that this life stage does not have functioning mouthparts, indicating that uptake of dsRNA does not depend on its ingestion. Suppression occurred with dsRNA presented in 'naked' or liposome-encapsulated forms, indicating that a liposome formulation was not necessary for uptake to occur. Adult worms also showed significant gene suppression, however, they did not show any reduced motility compared to controls over a 3-day period. Adult worms treated with ivermectin to paralyse their pharynx, still showed significant gene suppression, again suggesting that uptake of dsRNA does not require ingestion. We have shown that soaking in dsRNA is an effective method for RNAi with the parasitic stages of H. contortus, and, hence, may offer significant potential as a tool for studying gene function in this parasite species.