Nematode Survival Research Articles

Neurobehavior and neuron damage following prolonged exposure of silver nanoparticles with/without polyvinylpyrrolidone coating in Caenorhabditis elegans.

Silver nanoparticles (AgNPs) have become widespread in the environment with increasing industrial applications. But the studies about their potential health risks are far from enough, especially in neurotoxic effects. This study aimed to investigate the neurotoxic effects of longer-term exposure (prolonged exposure for 48 h and chronic exposure for 6 days) of 20nm AgNPs with/without polyvinylpyrrolidone (PVP) coating at low concentrations (0.01-10 mg·L-1 ) to Caenorhabditis elegans. The results suggested that exposure to AgNPs induced damage to nematode survival, with the longest and relative average life span reduced. Exposure to AgNPs caused neurotoxicity on locomotion behaviors (head thrashes, body bends, pharyngeal pumping frequency, and defecation interval) and sensory perception behaviors (chemotaxis assay and thermotaxis assay), as well as impaired dopaminergic, GABAergic, and cholinergic neurons, except for glutamatergic, based on the alters fluorescence intensity, in a dose- and time-dependent manner. Further investigations suggested that the low-dose AgNPs (0.01-0.1 mg·L-1 ) exposure raises receptors of GABAergic and dopamine in C.elegans at the genetic level, whereas opposite results were observed at higher doses (1-10 mg·L-1 ), which implied that AgNPs could cause neurotoxicity by impairing neurotransmitter delivery. The PVP-AgNPs could cause a higher fatality rate and neurotoxicity at the same dose. Notably, AgNPs did not cause any deleterious effect on nematodes at the lowest dose of 0.01 mg·L-1 . In general, these results suggested that AgNPs possess the neurotoxic potential in C.elegans and provided useful information to understand the neurotoxicity of AgNPs, which would offer an inspiring perspective on the safe application.

The effect of organic compost and soil texture on the survival and infectivity of entomopathogenic nematode species

To improve the efficacy of entomopathogenic nematodes (EPNs) as biocontrol agents in the field, knowledge about the kinds of impact, which the physical nature of the agricultural soil environment may have on nematode survival, persistence, and host location is important. The study aimed to investigate the effects which the addition of organic soil amendments would have on the duration of infectivity and survivorship of infective juveniles (IJs) belonging to Heterorhabditis bacteriophora in soils undergoing progressive moisture loss. The soil amendments involved mixing commercially available organic compost such as mulch, organic compost, professional potting mix, organic lawn dressing with two soil textural classes, namely loamy soil, and coarse river sand. Using Petri dish-based assays, the mulch soil amendment resulted in the highest Galleria mellonella larval mortality rate across different organic compost application concentrations (mass: mass basis). The type of compost used based on its feedstock composition, the concentration of nutrients, and organic matter mixed with a specific type of soil texture had a significant effect on the tolerance of EPNs to different dehydration periods. Virulence and efficacy decreased over 7 days of progressive dehydration. The use of organic compost did not have any detrimental effect on EPNs. The knowledge obtained could be applied to increase the effectiveness of entomopathogenic nematodes as biocontrol agents.

Evaluation of Barricade® to enhance survival of entomopathogenic nematodes on cowhide

Entomopathogenic nematodes (EPNs), Steinernema riobrave and Heterorhabditis floridensis are under evaluation for eradication of the southern cattle fever tick, Rhipicephalus microplus infesting nilgai antelope, in South Texas. Cattle fever ticks are a significant threat to the U.S. livestock industry. Although they have been eradicated in the U.S. they frequently re-invade along the Texas-Mexico border. Remotely operated field sprayers have been developed to directly treat nilgai antelope with EPNs as they transit fence crossings and as they contact wetted foliage and soil from the surrounding area. EPNs are known to be susceptible to mortality from ultraviolet light (UV) and desiccation. A sprayable fire gel, Barricade®, has been reported to protect EPNs from UV and desiccation but has not been tested on animal hides. Barricade® at 1 and 2 percent rates was mixed with the water solution of S. riobrave and H. floridensis and applied to cowhides (to mimic direct treatment of nilgai) and filter paper and then these substrates were placed out of doors in 0, 30, 60 or 120 min of sunlight. Wax moth larvae, Galleria mellonella, were exposed to the cowhides and filter paper to determine efficacy of the EPNs. Efficacy of S. riobrave with 1 and 2% Barricade® gel applied to cowhides was significantly improved at 30 and 60 min as compared to the control. At 120 min mortality of the wax moth larvae was near zero for both the control and the treatments. Similar results were found with the filter paper test. In contrast, efficacy of H. floridensis with Barricade® applied to cowhides or filter paper was not significantly improved at 30, 60 or 120 min as compared to the water only control. Barricade® has the potential to improve the efficacy of S. riobrave and other EPNs by reducing mortality and desiccation, especially when used in the remotely operated sprayer developed for treatment of cattle fever tick infested nilgai.

Mitigation of graphene oxide toxicity in C. elegans after chemical degradation with sodium hypochlorite

Graphene oxide (GO) is a promising and strategic carbon-based nanomaterial for innovative and disruptive technologies. It is therefore essential to address its environmental health and safety aspects. In this work, we evaluated the chemical degradation of graphene oxide by sodium hypochlorite (NaClO, bleach water) and its consequences over toxicity, on the nematode Caenorhabditis elegans. The morphological, chemical, and structural properties of GO and its degraded product, termed NaClO-GO, were characterized, exploring an integrated approach. After the chemical degradation of GO at room temperature, its flake size was reduced from 156 to 29 nm, while NaClO-GO showed changes in UV–vis absorption, and an increase in the amount of oxygenated surface groups, which dramatically improved its colloidal stability in moderately hard reconstituted water (EPA medium). Acute and chronic exposure endpoints (survival, growth, fertility, and reproduction) were monitored to evaluate material toxicities. NaClO-GO presented lower toxicity at all endpoints. For example, an increase of over 100% in nematode survival was verified for the degraded material when compared to GO at 10 mg L−1. Additionally, enhanced dark-field hyperspectral microscopy confirmed the oral uptake of both materials by C. elegans. Finally, this work represents a new contribution toward a better understanding of the links between the transformation of graphene-based materials and nanotoxicity effects (mitigation), which is mandatory for the safety improvements that are required to maximize nanotechnological benefits to society.

Natural enemies of herbivores maintain their biological control potential under short-term exposure to future CO2, temperature, and precipitation patterns.

Climate change will profoundly alter the physiology and ecology of plants, insect herbivores, and their natural enemies, resulting in strong effects on multitrophic interactions. Yet, manipulative studies that investigate the direct combined impacts of changes in CO2, temperature, and precipitation on the third trophic level remain rare. Here, we assessed how exposure to elevated CO2, increased temperature, and decreased precipitation directly affect the performance and predation success of species from four major groups of herbivore natural enemies: an entomopathogenic nematode, a wolf spider, a ladybug, and a parasitoid wasp. A four‐day exposure to future climatic conditions (RCP 8.5), entailing a 28% decrease in precipitation, a 3.4°C raise in temperature, and a 400 ppm increase in CO2 levels, slightly reduced the survival of entomopathogenic nematodes, but had no effect on the survival of other species. Predation success was not negatively affected in any of the tested species, but it was even increased for wolf spiders and entomopathogenic nematodes. Factorial manipulation of climate variables revealed a positive effect of reduced soil moisture on nematode infectivity, but not of increased temperature or elevated CO2. These results suggest that natural enemies of herbivores may be well adapted to short‐term changes in climatic conditions. These findings provide mechanistic insights that will inform future efforts to disentangle the complex interplay of biotic and abiotic factors that drive climate‐dependent changes in multitrophic interaction networks.

Field Validation of the Effect of Soil Fumigation of Ethanedinitrile (EDN) on the Mortality of Meloidogyne hapla and Carrot Yield Parameters

With the increasing importance of soilborne plant pest nematodes and the relatively recent phase-out of methyl bromide as a key soil fumigant, there is an urgent need for new fumigants with good nematicidal properties. Ethanedinitrile (EDN) is a promising fumigant and preparation because of its physical, agrochemical, and nematicidal properties. However, its efficacy against nematode pests of different crops under field conditions has not been fully validated and understood. Therefore, the aim of our study was to evaluate the effect of two concentrations of EDN on the survival of northern root-knot nematodes (Meloidogynehapla) and on carrot yield and quality under field conditions. The evaluation was performed using naturally infested carrot plots, and EDN application to the soil was followed by covering the treated area with film. A high biological effect was observed for both EDN concentrations tested, with even the lower dose (30 g·m−2) being sufficient for M. hapla suppression. Positive effects of EDN application—likely due to EDN partial conversion into biologically available nitrogen in soil—on carrot root weight, in comparison with the untreated control, were also observed.

Winter cover crops as reservoirs of tobacco rattle virus (TRV) and hosts of root-lesion, root knot and stubby-root nematodes

A greenhouse pot study was conducted on four cover crops (annual ryegrass, perennial tetraploid ryegrass, winter wheat cv. ‘Caledonia’ and sorghum-sudangrass) and one rotation crop (sweet corn cv. ‘Sheba’) to compare the efficiency of these crop species as hosts of Paratrichodorus minor (Colbran) Siddiqi, and the ability of the nematodes to acquire tobacco rattle virus (TRV) from roots of infected plants and re-transmit it to healthy plants. P. minor reproduced rapidly on sorghum-sudangrass and sweet corn and re-transmitted the virus to indicator plants. Annual ryegrass, perennial ryegrass, and winter wheat cv. ‘Caledonia’, all of which re-transmitted TRV poorly in the greenhouse, were evaluated in two years of field studies for fall establishment and soil coverage, nutrient sequestration, effect on parasitic nematode populations and on subsequent potato crops. Annual ryegrass performed best overall in terms of establishment, ground cover, overwintering survival and foliar biomass production. None of the cover crops had a consistently significant effect on populations of parasitic nematodes in field plots, including Pratylenchus, Paratrichodorus, and Meloidogyne. Both ryegrass cover crops appeared to provide a favourable environment for survival of root knot nematodes (Meloidogyne spp.), although they are not considered to be hosts of this nematode. There was no difference in soil carbon, nitrogen or potato yield following any cover crop. Symptoms of corky ringspot were not observed in the field and TRV was not detected in potato plants by RT-PCR.

Biological suppression of the root-knot nematode Meloidogyne incognita following winter cover crops in conservation tillage cotton

Winter cover crops are often planted in temperate and subtropical environments. The residue from these cover crops may enhance suppression of plant-parasitic nematodes by providing alternative food sources for predators and parasites. The primary objective of this study was to determine whether winter cover crops enhance early season suppression of Meloidogyne incognita compared to a weedy fallow. Two secondary objectives were to determine the effect of winter cover crops on free-living nematodes, with an emphasis on carnivorous (Ca; obligate predators) and omnivorous (Om, facultative predators) nematodes, and determine the role of these predators in suppression of M. incognita. Two experiments were conducted over 3 years at different field sites. The experiments consisted of three cover crop treatments replicated four times in a randomized complete block design. The cover crop treatments for the Jones Farm were rye, a rye-crimson clover combination, and fallow. The cover crop treatments for the Belflower Farm were rye, hairy vetch, and fallow. The cover crops were killed and the fields planted with cotton. At the time of planting cotton, soil samples were collected to conduct bioassays to evaluate suppression of M. incognita and abundance of predatory nematodes. One bioassay measured nematode survival after 5 days in natural compared to defaunted soil, and the other bioassay measured differences in nematode reproduction among the cover-crop treatments. The native soil community reduced survival of M. incognita J2 by 55% in 2016 at the Belflower Farm and in all years at the Jones Farm by 60% compared to defaunated soil; however, the cover crop treatments had no effect on the level of suppression. Predatory nematodes may have contributed to reduced survival. Like the survival bioassay, predators were also generally not influenced by cover crop treatment. At the Jones Farm, there was a significant correlation between relative abundance of Om, Ca, and Om + Ca and suppression of J2. Reproduction of M. incognita was suppressed in soil that had been planted to cover crops by 54–66% compared to the weedy fallow at the Belflower but not the Jones Farm. Planting winter cover crops enhanced early season suppression of M. incognita reproduction at the Belflower Farm; however, cover crops had no effect on suppression of J2 survival at the Jones Farm. Enhancement of nematode suppression by cover crops is likely dependent on the organisms involved in suppression.

Wolbachia-Filarial Nematode Interactions: Embryological, Cellular and Molecular Aspects and Therapeutic Targets

Filarial nematodes including Wuchereria bancrofti, Onchocerca volvulous, Brugia malayi, B. timori and Loa loa cause some of the most common parasitic infections in humans including elephantiasis, blindness and skin lesions. Wolbachia, an α-proteobacterium is the most widespread endosymbiotic bacterium widely present in various insect species, in parasitic nematodes of animals and also in the plant-parasite nematode, Radopholus similis. In insects, they harbour in male and female germlines and in a variety of somatic tissues. In filarial nematodes, they live as reproductive endosymbionts in ovarian tissues, oocytes and oogonia and newly forming embryos within the uterus and affect moulting, reproduction and survival of the host nematode. They provide essential metabolites such as riboflavin, haem and nucleotides to the host nematodes, but they cannot synthesize some vitamins, coenzyme A, NAD, biotin, folate, ubiquinone, lipoic acid etc. de novo due to incomplete biochemical pathways, and derive those from host nematodes. Thus, there is an obligate symbiotic relationship between Wolbachia and host nematode. Antibiotic treatment against Wolbachia has been proved as a promising target for prevention of filariasis which can break the parasitic cycle. Genomic studies regarding embryological, cellular and molecular aspects of Wolbachia and filarial nematode are still limited. Further research in this area could employ Wolbachia-filarial nematode interactions as a potential therapeutic target to reduce or prevent filarial infections.

The impact of chemical nematicides on entomopathogenic nematode survival and infectivity

Abstract Entomopathogenic nematodes (EPNs) belonging to the genera, Steinernema and Heterorhabditis, occur naturally in the soil along with plant-parasitic nematodes which are important root pests of many different crops. Here, we report the effects of four registered nematicidal compounds (fluopyram, fosthiazate, metam potassium, and fenamiphos) that are used for the control of PPNs on the survival, virulence, penetration efficiency, and reproduction of S. carpocapsae and H. bacteriophora. Despite previous studies warning of the impact of nematicidal compounds on IJ survival and infectivity, none have assessed their impact on EPN chemotaxis, penetration into and reproduction in insect host or conducted longer term soil assays. Survival of EPNs, based on observing IJ movement under a stereomicroscope after incubation in different concentrations of nematicides, showed that ≥ 80% of both nematode species were killed by fosthiazate, fenamiphos and metam potassium within 24 h. The recommended concentration of fluopyram killed 33% of H. bacteriophora, and 28% of S. carpocapsae after 48 h exposure. IJs exposed to the nematicides were less virulent against Galleria mellonella larvae in sand bioassay to non-treated IJs as significantly more control IJs of both EPN species penetrated their insect host (~47% of IJs added) than IJs exposed to fluopyram and fosthiazate; and the number of IJ progeny emerging from these controls was significantly higher than the number of IJ progeny emerging from IJs treated with the nematicidal compounds. In a highly novel discovery, the chemotaxis experiments using Pluronic F-127 gel indicated that H. bacteriophora were repelled from nematicide-treated environments. Moreover, IJs of both species added to treated natural loamy-clay soil at 5-day-intervals for 30 days post application of nematicides were generally unable to induce G. mellonella mortality, except for S. carpocapsae IJs added to fosthiazate-treated soil. Overall, our study indicates that there were detrimental effects of the nematicides on EPN IJs in treated soil. Therefore, overlap in timing for control of PPNs and the use of EPNs for biological insect control must be avoided. Future studies should assess the optimization of timing for nematicides use and survival and infectivity of IJs in the soil.

Broad-Spectrum Activity of Volatile Organic Compounds from Three Yeast-like Fungi of the Galactomyces Genus Against Diverse Plant Pathogens

The application of antagonistic fungi for plant protection has attracted considerable interest because they may potentially replace the use of chemical pesticides. Antipathogenic activities confirmed in volatile organic compounds (VOCs) from microorganisms have potential to serve as biocontrol agents against pre- and post-harvest diseases. In the present study, we investigated Galactomyces fungi isolated from rotten leaves and the rhizosphere of cherry tomato (Lycopersicon esculentum var. cerasiforme). VOCs produced by Galactomyces fungi negatively affected the growth of phytopathogenic fungi and the survival of nematodes. Mycelial growths of all nine examined phytopathogenic fungi were inhibited on agar plate, although the inhibition was more intense in Athelia rolfsii JYC2163 and Cladosporium cladosporioides JYC2144 and relatively moderate in Fusarium sp. JYC2145. VOCs also efficiently suppressed the spore germination and mycelial growth of A. rolfsii JYC2163 on tomatoes. The soil nematode Caenorhabditis elegans exhibited higher mortality in 24 h in the presence of VOCs. These results suggest the broad-spectrum activity of Galactomyces fungi against various plant pathogens and the potential to use VOCs from Galactomyces as biocontrol agents.

Aprepitant, an antiemetic agent, interferes with metal ion homeostasis of Candida auris and displays potent synergistic interactions with azole drugs

ABSTRACT With the rapid increase in the frequency of azole-resistant species, combination therapy appears to be a promising tool to augment the antifungal activity of azole drugs against resistant Candida species. Here, we report the effect of aprepitant, an antiemetic agent, on the antifungal activities of azole drugs against the multidrug-resistant Candida auris. Aprepitant reduced the minimum inhibitory concentration (MIC) of itraconazole in vitro, by up to eight-folds. Additionally, the aprepitant/itraconazole combination interfered significantly with the biofilm-forming ability of C. auris by 95 ± 0.13%, and significantly disrupted mature biofilms by 52 ± 0.83%, relative to the untreated control. In a Caenorhabditis elegans infection model, the aprepitant/itraconazole combination significantly prolonged the survival of infected nematodes by ~90% (five days post-infection) and reduced the fungal burden by ~92% relative to the untreated control. Further, this novel drug combination displayed broad-spectrum synergistic interactions against other medically important Candida species such as C. albicans, C. krusei, C. tropicalis, and C. parapsilosis (ƩFICI ranged from 0.08 to 0.31). Comparative transcriptomic profiling and mechanistic studies indicated aprepitant/itraconazole interferes significantly with metal ion homeostasis and compromises the ROS detoxification ability of C. auris. This study presents aprepitant as a novel, potent, and broad-spectrum azole chemosensitizing agent that warrants further investigation.

In the Model Host Caenorhabditis elegans, Sphingosine-1-Phosphate-Mediated Signaling Increases Immunity toward Human Opportunistic Bacteria.

Sphingosine-1-phophate (S1P) is a sphingolipid-derived signaling molecule that controls diverse cellular functions including cell growth, homeostasis, and stress responses. In a variety of metazoans, cytosolic S1P is transported into the extracellular space where it activates S1P receptors in a concentration-dependent manner. In the free-living nematode Caenorhabditis elegans, the spin-2 gene, which encodes a S1P transporter, is activated during Gram-positive or Gram-negative bacterial infection of the intestine. However, the role during infection of spin-2 and three additional genes in the C. elegans genome encoding other putative S1P transporters has not been elucidated. Here, we report an evolutionally conserved function for S1P and a non-canonical role for S1P transporters in the C. elegans immune response to bacterial pathogens. We found that mutations in the sphingosine kinase gene (sphk-1) or in the S1P transporter genes spin-2 or spin-3 decreased nematode survival after infection with Pseudomonas aeruginosa or Enterococcus faecalis. In contrast to spin-2 and spin-3, mutating spin-1 leads to an increase in resistance to P. aeruginosa. Consistent with these results, when wild-type C. elegans were supplemented with extracellular S1P, we found an increase in their lifespan when challenged with P. aeruginosa and E. faecalis. In comparison, spin-2 and spin-3 mutations suppressed the ability of S1P to rescue the worms from pathogen-mediated killing, whereas the spin-1 mutation had no effect on the immune-enhancing activity of S1P. S1P demonstrated no antimicrobial activity toward P. aeruginosa and Escherichia coli and only minimal activity against E. faecalis MMH594 (40 µM). These data suggest that spin-2 and spin-3, on the one hand, and spin-1, on the other hand, transport S1P across cellular membranes in opposite directions. Finally, the immune modulatory effect of S1P was diminished in C. elegans sek-1 and pmk-1 mutants, suggesting that the immunomodulatory effects of S1P are mediated by the p38 MAPK signaling pathway.

Survival of Pratylenchus brachyurus under dry soil conditions

Pratylenchus brachyurus, a root-lesion nematode, depends on host plants for growth and survival. Weeds, volunteer plants, and crop root residues may act as reservoirs for the parasite in the field, but little is known about the ability of P. brachyurus to survive in the absence of a host. This study aimed to evaluate P. brachyurus survival and infectivity in artificially and naturally infested soil under dry conditions. Two experiments were conducted, the first using artificially infested soil and the second using naturally infested soil. Soil samples were inoculated with a nematode suspension or infected root fragments. At 0, 30, 60, and 90 days post-inoculation, pots were planted with nematode-susceptible maize and soybean. Fallow pots were also analyzed. Nematode survival, infectivity, and morphology were determined 30 days after planting. P. brachyurus showed enhanced survival in soil in the presence of root fragments. However, inoculation method had no effect on the ability of surviving nematodes to infect host roots. Parasites showed signs of anhydrobiosis (C-shaped or tightly coiled body) after 90 and 120 days under dry conditions.

Response of life-history traits of estuarine nematodes to the surfactant sodium dodecyl sulfate

Species responses to stress are expected to be dependent on their life-history strategy. In this study, we compare the responses of two free-living marine nematodes, Litoditis marina and Diplolaimella dievengatensis, both considered opportunistic, fast-growing, and stress-tolerant species, to the exposure to sublethal concentrations of sodium dodecyl sulfate (SDS) surfactant. Specifically, we evaluated the growth and reproduction rates, as well as the survival of individuals exposed from eggs and/or juveniles (J1) onwards. Exposure to SDS significantly affected the growth and reproduction rates of both species. However, whereas growth and reproduction rates of D. dievengatensis were significantly enhanced at low and intermediate concentrations of SDS (0.001% and 0.003%), for L. marina both parameters were significantly reduced by all SDS concentrations tested (0.001%, 0.003% and 0.006%). Exposure to SDS did not affect the survival of adult nematodes of D. dievengatensis, while for L. marina, survival of males exposed to 0.006% SDS was significantly reduced compared to the control. Responses of the life-history traits growth, fecundity and survival did not exhibit clear trade-offs. The contrasting responses of D. dievengatensis and L. marina indicate that biologically and ecologically similar species can have remarkably distinct tolerances to stress, and that, in agreement with recent studies, rhabditid nematodes cannot a priori be considered very stress tolerant. Consequently, single species traits and phylogenetic relatedness are poor predictors of nematode responses to toxic stress posed by anthropogenic activities.

Response of soybean cyst nematode (Heterodera glycines) and root-knot nematodes (Meloidogyne spp.) to gradients of pH and inorganic salts

Plant-parasitic nematodes are able to sense and respond to gradients of chemical signals. How pH and inorganic salts in the rhizosphere affect nematode accumulation and host-seeking is poorly understood. We investigate the response of different groups of plant-parasitic nematodes to pH and salt concentration gradients. Responses of infective juveniles (J2) of the economically important plant-parasitic nematodes, soybean cyst nematodes (SCN; Heterodera glycines) and root-knot nematodes (RKN; Meloidogyne incognita and M. hapla) to pH and salt gradients were assessed using Pluronic F-127 gel-based assays. Microelectrodes were utilized to measure pH and ion concentration gradients in the gel. Differences were found between the three nematode species in response to acid, base and salts. For SCN, maximum nematode accumulation was between pH range 4.98–5.46 in an acid gradient, while the preferred alkaline pH ranges were 8.40–8.78 and 9.52–9.99. The preferred Cl− concentration for SCN attraction was 171–256 mM. RKN showed weak attraction to base and salt at low J2 concentration but increasing attraction at a greater nematode concentration. The pH and inorganic salts affect nematode behavior, accumulation, and survival. These findings provide new considerations for strategies to manage plant-parasitic nematodes under field conditions.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to −2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.

Corynebacterium diphtheriae Virulence Analyses Using a Caenorhabditis elegans Model.

Corynebacterium diphtheriae is the leading cause of pharyngeal diphtheria, a respiratory disease characterized by formation of a pseudomembrane at the site of infection. Although outbreaks of C. diphtheriae infections are rare nowadays, the emergence of multidrug-resistant C. diphtheriae strains is one of the most significant public health concerns worldwide. Although C. diphtheriae has been studied for more than a century and diphtheria toxin and pili have been identified as major virulence factors, little is known about factors involved in bacterial colonization and development of disease. Here, we describe the utilization of Caenorhabditis elegans as a cost-effective, versatile model of infection to evaluate C. diphtheriae virulence. We provide detailed protocols for nematode synchronization and for evaluation of nematode survival and formation of a deformed anal region induced by C. diphtheriae infection. These protocols will permit future high-throughput screenings of virulence factors in C. diphtheriae and advance our knowledge of C. diphtheriae pathogenesis. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Synchronization of nematodes Basic Protocol 2: Assay for nematode survival following C. diphtheriae infection Basic Protocol 3: Assays for bacterial colonization and formation of deformed anal region.

Evaluation of the potential toxicity of haloperidol, clozapine and a new putative antipsychotic molecule, PT-31, in an alternative toxicity model, C. elegans

Schizophrenia is a disabling mental illness that affects approximately 1% of the world population. The treatment of this disorder is based on two generations of substances, typical antipsychotics, such as haloperidol, and atypical antipsychotics, such as clozapine, which can cause severe adverse effects. Therefore, the development of novel molecules that are safe and efficacious to treat the disease is crucial. PT-31 is a putative α2-adrenoceptor agonist effective against schizophrenia positive and cognitive symptoms in mice. C. elegans is an alternative model that has been successfully used to investigate the toxicity of a variety of substances. The present study aimed to evaluate the potential toxicity of the new molecule PT-31 and the antipsychotics haloperidol and clozapine in C. elegans. The evaluation was carried out based on toxicity endpoint tests, survival, developmental and behavioral assays. The antipsychotics haloperidol and clozapine decreased nematode survival by 30 and 40%, respectively, exposing the potential toxicity of these substances whereas PT-31 was safer based on this parameter. Similar results were obtained in the nematode developmental assay: haloperidol and clozapine significantly reduced nematode body length and area, whereas PT-31 preserved the normal development of the nematodes. The behavioral assessment was based on the frequency of body bends; none of the antipsychotics affected the locomotion rate of the nematodes, and PT-31 also did not compromise this parameter, demonstrating the safety of this new compound and reinforcing the recognized toxicity of antipsychotics.

Effects of temperatures on survival of Aphelenchoides besseyi in prolonged storage of rice grains

Summary The white-tip nematode, Aphelenchoides besseyi, is a seed-borne ectoparasite of the rice plant Oryza sativa. Nematodes in dried rice seeds are in dehydrated quiescence or anhydrobiosis and are reactivated by rehydration. To understand the persistent parasitism better, the effects of temperature on nematode survival were examined during prolonged periods of seed storage. There was a marked difference in the survival rate among different temperatures; survival was lower at 20 and 25°C than at −5 to 10°C after storage for 190 days. No nematodes survived a storage period of 1313 days at 20 and 25°C. When rice seeds were held at 5°C, the survival rate of nematodes decreased during a period of 7315 days. The estimated instantaneous rate of mortality per month was higher in the early and late parts of the period than in the middle part. Another nematode population also showed a reduction in the survival rate during 6553 days storage at 5°C. In storage at −30°C, survival was not affected during a period of 6485 days. After storage at −30°C for 6546 days, 96% of rice seeds germinated, whereas 60-96% of seeds of two groups germinated after storage at 5°C for 6610-7373 days. Therefore, prolonged storage of rice seeds at 5 or −30°C was unlikely to disrupt the connection between rice plants and A. besseyi.