Structure, development, and evolutive patterns of spermatozoa in rhabditid nematodes (Nematoda: Rhabditida)

Spermatogenesis of five rhabditid nematodes was studied using transmission electron microscopy and is described herein. Structure and development of nematode sperm in all available representatives of the extensive order Rhabditida have been analysed and the main characteristics of each infraorder are discussed. The ancestral sperm of the order Rhabditida was reconstructed using maximum likelihood and Bayesian methods based on 44 ultrastructural sperm characters. The hypothetical ancestral spermatogenesis of the order Rhabditida agrees with the previously suggested "rhabditid" pattern and appears to be conserved throughout the order Rhabditida. Despite the enormous variation of rhabditid nematodes, few groups deviate from the ancestral pattern. This conserved pattern can be informative within the phylum Nematoda at order level, but poses limitations when used in taxonomic and phylogenetic analysis within Rhabditida.

Morphological adjustment in free-living Steinernema feltiae infective juveniles to increasing concentration of Nemafric-BL phytonematicide

Third-stage larvae (L3) of Steinernema feltiae exist as free-living infective juveniles (IJ), with suspended development activities. In contrast, parasitic stages (L1, L2, L4, adult) have mutualistic relations with Xenorhabdus species bacteria, along with unique morphological changes and development inside the cadaver of host insects and/or plant-parasitic nematodes. Commercial IJ strains are tolerant to cucurbitacin-containing phytonematicides, but we have scant information on how morphological adjustments in IJ are achieved. In this study, we investigated the nature of morphological adjustments in commercial S. feltiae IJ strains to Nemafric-BL phytonematicide, which contains cucurbitacin B as active ingredient. Post-72 h exposure to phytonematicide concentration, IJ specimens were fixed on mounting slides. Length (body, excretory pore to anterior end, pharynx, rectum, stoma, tail), diameter (head width, neck base, mid-body, anal body), cuticle thickness and De Man ratios were measured with a computer software programme attached to Omax light microscope. Morphometric data against increasing phytonematicide concentration exhibited either density-dependent quadratic, linear or neutral relations. Increase in body length at low phytonematicide concentration was accompanied by decrease in tail length and pharynx length during muscle contraction when IJ were still alive. After death at high phytonematicide concentration, the opposite morphometric effects ensued due to muscle relaxation. The observed changes in morphometric structures were explained on the basis of morphological adjustments that modulated volumes of pseudocoelom cavity in IJ. The modulation is intended to maintain hydrostatic pressure within permissible upper limits in order to avoid structural damage to internal organs embedded in the pseudocoelom fluids.

Transcriptomic analysis of Baltic cod (Gadus morhua) liver infected with Contracaecum osculatum third stage larvae indicates parasitic effects on growth and immune response

High infection levels due to third-stage larvae of the anisakid nematode Contracaecum osculatum have been documented in cod from the eastern part of the Baltic sea during the latest decades. The nematode larvae mainly infect the liver of Baltic cod and prevalence of infection has reached 100% with a mean intensity up to 80 parasites per host in certain areas and size classes. Low condition factors of the cod have been observed concomitant with the rise in parasite abundance suggesting a parasitic effect on growth parameters. To investigate any association between parasite infection and physiological status of the host we performed a comparative transcriptomic analysis of liver obtained from C. osculatum infected and non-infected cod. A total of 47,025 predicted gene models showed expression in cod liver and sequences corresponding to 2084 (4.43%) unigenes were differentially expressed in infected liver when compared to non-infected liver. Of the differentially expressed unigenes (DEGs) 1240 unigenes were up-regulated while 844 unigenes were down-regulated. The Gene Ontology (GO) enrichment analysis showed that 1304 DEGs were represented in cellular process and single-organism process, cell and cell part, binding and catalytic activity. As determined by the Kyoto Encyclopedia of Gene and Genomes (KEGG) Pathways analysis, 454 DEGs were involved in 138 pathways. Ninety-seven genes were related to metabolic pathways including carbohydrate, lipid, and amino acid metabolism. Thirteen regulated genes were playing a role in immune response such as Toll-like receptor signaling, NOD-like receptor signaling, RIG-I-like receptor signalling and thirty-six genes were associated with growth processes. This indicates that the nematode infection in Baltic cod may affect on molecular mechanisms involving metabolism, immune function and growth.

Mild thermal stress affects Steinernema carpocapsae infective juvenile survival but not protein content

Steinernema nematodes and their Xenorhabdus symbionts are a malleable model system to study mutualistic relations. One of the advantages they possess is their ability to be disassociated under in vitro rearing conditions. Various in vitro methods have been developed to produce symbiont colonized and aposymbiotic (symbiont-free) nematodes. Until now, there has been no investigation on how in vitro rearing conditions may have an impact on the storage ability and the protein content of the infective juvenile at different storage temperatures. Thus, in this study, we investigated how infective juvenile longevity and protein content are impacted when the nematodes were reared with two in vitro methods (lipid and liver kidney agar) considering colonized and uncolonized nematodes, and under two different temperatures: 15 °C and 20 °C (mild stress). Infective juveniles reared in vitro (with or without their symbionts) had lower 8-week survival rates. No in vitro reared, colonized IJs survived to the desired 16-week time point. Survival of infective juveniles stored under mild stress temperature (20 °C) was lower than that observed at 15 °C. However, when comparing the interaction between rearing condition and storage temperature, there were not significant differences. With respect to protein content, in vivo, colonized infective juveniles maintained a static protein content over time, suggesting symbiont colonization may influence protein metabolism and/or turnover in infective juveniles.

Biochars from olive mill waste have contrasting effects on plants, fungi and phytoparasitic nematodes

Olive mill waste (OMW), a byproduct from the extraction of olive oil, causes serious environmental problems for its disposal, and extensive efforts have been made to find cost-effective solutions for its management. Biochars produced from OMW were applied as soil amendment and found in many cases to successfully increase plant productivity and suppress diseases. This work aims to characterize biochars obtained by pyrolysis of OMW at 300 °C to 1000 °C using ¹³C NMR spectroscopy, LC-ESI-Q-TOF-MS and SEM (Scanning Electron Microscopy). Chemical characterization revealed that biochar composition varied according to the increase of pyrolysis temperature (PT). Thermal treated materials showed a progressive reduction of alkyl C fractions coupled to the enrichment in aromatic C products. In addition, numerous compounds present in the organic feedstock (fatty acids, phenolic compounds, triterpene acids) reduced (PT = 300 °C) or completely disappeared (PT ≥ 500 °C) in biochars as compared to untreated OMW. PT also affected surface morphology of biochars by increasing porosity and heterogeneity of pore size. The effects of biochars extracts on the growth of different organisms (two plants, one nematode and four fungal species) were also evaluated. When tested on different living organisms, biochars and OMW showed opposite effects. The root growth of Lepidium sativum and Brassica rapa, as well as the survival of the nematode Meloidogyne incognita, were inhibited by the untreated material or biochar produced at 300 °C, but toxicity decreased at higher PTs. Conversely, growth of Aspergillus, Fusarium, Rhizoctonia and Trichoderma fungi was stimulated by organic feedstock, while being inhibited by thermally treated biochars. Our findings showed a pattern of association between specific biochar chemical traits and its biological effects that, once mechanistically explained and tested in field conditions, may lead to effective applications in agriculture.

Establishing RNAi in a Non-Model Organism: The Antarctic Nematode Panagrolaimus sp. DAW1

The Antarctic nematode Panagrolaimus sp. DAW1 is one of the only organisms known to survive extensive intracellular freezing throughout its tissues. Although the physiological mechanisms of this extreme adaptation are partly understood, the molecular mechanisms remain largely unknown. RNAi is a method that allows the examination of gene function in a direct, targeted manner, by knocking out specific mRNAs and revealing the effects on the phenotype. In this study we have explored the viability of RNAi in Panagrolaimus sp. DAW1. In the first trial, nematodes were fed E. coli expressing Panagrolaimus sp. DAW1 dsRNA of the embryonic lethal genes rps-2 and dhc, and the blister gene duox. Pd-rps-2(RNAi)-treated nematodes showed a significant decrease in larval hatching. However, qPCR showed no significant decrease in the amount of rps-2 mRNA in Pd-rps-2(RNAi)-treated animals. Several soaking protocols for dsRNA uptake were investigated using the fluorescent dye FITC. Desiccation-enhanced soaking showed the strongest uptake of FITC and resulted in a significant and consistent decrease of mRNA levels of two of the four tested genes (rps-2 and tps-2a), suggesting effective uptake of dsRNA-containing solution by the nematode. These findings suggest that RNAi by desiccation-enhanced soaking is viable in Panagrolaimus sp. DAW1 and provide the first functional genomic approach to investigate freezing tolerance in this non-model organism. RNAi, in conjunction with qPCR, can be used to screen for candidate genes involved in intracellular freezing tolerance in Panagrolaimus sp. DAW1.

Life history trait analysis of the entomopathogenic nematode Steinernema feltiae provides the basis for prediction of dauer juvenile yields in monoxenic liquid culture

Entomopathogenic nematodes (Steinernema spp.) are used in integrated pest management to control insect pests in cryptic environments. The nematodes are mass produced in monoxenic liquid culture with their symbiotic bacteria Xenorhabdus spp. For a better understanding of nematode population dynamics, the life history traits (LHTs) of the entomopathogenic nematode Steinernema feltiae were assessed at 25 °C by observing single pairs of male and female nematodes using a hanging drop technique. To investigate the influence of different food supplies on nematode reproduction, the LHTs were assessed with a daily supply of 5 ×, 10 × and 20 × 10(9) cells ml(-1) of the nematode's bacterial symbiont Xenorhabdus bovienii in semi-solid nematode growth gelrite (NGG) medium. Increasing bacterial density had a significant positive influence on the average number of offspring produced, which ranged from 359 to 813 per female. The intrinsic rate of natural increase r m, which ranges from 1.10 to 1.19 day(-1), was neither influenced by the bacterial density, nor was the mean generation time T (5.12-5.25 days) and population doubling time (PDT) (0.64-0.59 days). The average lifespan of reproductive females, which ranged from 6.7 to 7.3 days, was positively correlated with bacterial density. A positive correlation between female body volume and bacterial density was recorded (R = 0.67) as well as a significant positive correlation between female body size and offspring production (R = 0.89) in hanging drops. Whether these data can be used to predict nematode yields in liquid culture was tested. The total female body volume calculated as the average female body volume × total number of parental females per millilitre 3 days after nematode inoculation was positively correlated (R = 0.72) with nematode yields. The total female body volume on process day 3 is thus a good indicator for the estimation of nematode yield at the end of the process (12-15 days post dauer juvenile (DJ) inoculation) in both Erlenmeyer flasks and bioreactors. With a mean deviation of 9467 DJs ml(-1), the error resembles approximately 5 % of the final DJ yields.

Desiccation and cold storage of Galleria mellonella cadavers and effects on in vivo production of Steinernema carpocapsae

BACKGROUND

Direct application of insect cadavers infected with entomopathogenic nematodes (EPN) can successfully control target pest insects. Little is known about the effects of environmental factors (desiccation and temperature) on the production process for infective juveniles (IJ) in insects.

RESULTS

We examined the effects of desiccation time and cold storage (6.7 °C) on IJ production of the nematode Steinernema carpocapsae in Galleria mellonella cadavers at 30.8 and 57% humidity. Under desiccation, the IJ yield in cadavers increased gradually and reached a maximum on day 5. IJ yield gradually declined from day 6 onwards and was almost zero by day 15. In general, cold storage at 6.7 °C caused negative effects on IJ production in desiccated cadavers. Approximately 56 h post infection was the time at which nematodes were most sensitive to low temperatures during development in cadavers. Five-day desiccated cadavers generated higher mortality and more rapid death of Galleria mellonella larvae than using newly (day 0) desiccated cadavers.

CONCLUSION

This study describe methods of optimizing rearing techniques such as desiccation and cold storage to promote the mass production and application of EPN- infected host cadavers for the field control of insect pests.

EVALUATION OF VIRULENCE OF STEINERNEMA CARPOCAPSAE TO EUROPEAN MOLE CRICKET GRYLLOTALPA GRYLOTALPA L

Common European mole cricket (CEML) Grillotalpa grillotalpa L causes damage to field, vegetable crops, and small fruits growing at commercial plantations and nurseries. Chemical control if insecticides are used in poison bates, soil application or seedling/bulbs treatment is not environmentally friendly. Inundative and innoculative release of CTVL biocontrol agents, in particularly, Entomopathogenic nematode is a reliable alternative to chemical control. At the laboratory study the comparison of the ability of commercial strain (Nemastar) and local Ukrainian isolate of Steinernema carpocapsae in various concentrations to parasite in last instar nymph and adults of G. grillotalpa was investigated. Grillotalpa grillotalpa was found as a susceptible host for both commercial and local strains of S. carpocapsae. The life cycle of S. carpocapsae both strains in the adults of G. grillotapla with concentration 50 IJs per larva has been completed 12-15 days at t=25 C. Two generations of S. carpocapsae were able to develop in mole cricket for both strains. Two strains of S. carpocapsae nematode species tested were pathogenic to adults of G. grillotalpa. The mortalities of G. grillotapla last last instars' larva caused by S. carpocapsae were recorded in every concentration tested at least 20 to 150 IJs per larva. Mean larval mortality ranged from 48% to 95% depending upon nematode strain and rate of application. Larval mortality generally increased with increasing of nematode rates. It was significant for both S. carpocapsae strains (Ukr. Isolate F = 26 > 2,86) and commercial strain (Nemastar F = 102,95 > 2,86). Ukrainian local isolate caused a greater percentage of mortality of G. grillotapla adult than commercial strain of S. carpocapsae tested but interactions between nematode strains, application rates were not significant. This study presents new data on effect of S. carpocapsae isolated for Ukraine to key agricultural polyphagous pest G. grillotalpa susceptibility screening under controlled conditions, as presented in this paper is the first step towards the development of a biological control program of G. grillotaplpa by using of entomopathogenic nematodes.

Biological control agent of larger black flour beetles (Coleoptera: Tenebrionidae): a nuisance pest developing in cotton gin trash piles

The larger black flour beetles, Cynaeus angustus (LeConte) (Coleoptera: Tenebrionidae), feeds on saprophytic fungi found in gin trash piles and occasionally becomes a nuisance pest in adjacent homes and businesses. The potential of Steinernema carpocapsae 'NY 001,' as a potential control agent of larger black flour beetle under experimental conditions was examined with particular reference to the importance of soil moisture content. Without prospects of insecticides being labeled for control of larger black flour beetle in gin trash, the data presented here support further research into applications of entomopathogenic nematodes underneath gin trash piles as a way to minimize risk of larger black flour beetle populations causing nuisance to nearby homes and businesses.

Interaction of the koinobiont parasitoid Microplitis rufiventris of the cotton leafworm, Spodoptera littoralis, with two entomopathogenic rhabditids, Heterorhabditis bacteriophora and Steinernema carpocapsae

Entomopathogenic nematodes are generally considered beneficial organisms. However, they can affect beneficial insects such as parasitoids. The interaction between the entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and Steinernema carpocapsae Weiser, and the parasitoid Microplitis rufiventris Kokujev (Hymenoptera: Braconidae) was investigated in the laboratory. In non-parasitized hosts, Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) larvae exposed to H. bacteriophora showed a higher percent mortality than those exposed to S. carpocapsae. Both nematodes were able to invade and propagate in non-parasitized S. littoralis larvae and those parasitized by M. rufiventris. Both nematode species reproduced in Microplitis-parasitized hosts, but there was a higher number of nematodes in non-parasitized larvae. S. carpocapsae yielded higher numbers of infective juveniles than H. bacteriophora. Generally, the number of nematodes harvested increased as their host's size increased. The interaction between the nematodes and parasitoid favored the nematodes when the nematodes were inoculated during the parasitoid egg stage or the young parasitoid larvae, thus giving the nematodes a better chance to grow and reproduce, resulting in the death of the parasitoid larvae. Conversely, when the nematodes were inoculated during the late larval instar of the parasitoid, the competition partially favored the wasp, thus giving approximately 50% of the wasps a better chance to develop, emerge, and reproduce, providing evidence that both nematodes and wasps could reproduce in the same host. Egg maturation of female wasps derived from nematode-infected hosts was not significantly different than those from control hosts. The combined application of nematodes and parasitoids may be beneficial if the detrimental effects of the nematodes on the parasitoid could be avoided by precisely timing the application strategies. It is clear that Microplitis larvae and the nematodes share the host larva and engage in a trophic interaction with each other. Intraguild predation is briefly discussed.

Pepsin-like aspartic protease (Sc-ASP155) cloning, molecular characterization and gene expression analysis in developmental stages of nematode Steinernema carpocapsae

Steinernema carpocapsae is an insect parasitic nematode associated with the bacterium Xenorhabdus nematophila. These symbiotic complexes are virulent against the insect host. Many protease genes were shown previously to be induced during parasitism, including one predicted to encode an aspartic protease, which was cloned and analyzed in this study. A cDNA encoding Sc-ASP155 was cloned based on the EST fragment. The full-length cDNA of Sc-ASP155 consists of 955 nucleotides with multiple domains, including a signal peptide (aa1-15), a pro-peptide region (aa16-45), and a typical catalytic aspartic domain (aa71-230). The putative 230 amino acid residues have a calculated molecular mass of 23,812Da and a theoretical pI of 5.01. Sc-ASP155 blastp analysis showed 40-62% amino acid sequence identity to aspartic proteases from parasitic and free-living nematodes. Expression analysis showed that the sc-asp155 gene was up-regulated during the initial parasitic stage, especially in L3 gut and 6h induced nematodes. Sequence comparison revealed that Sc-ASP155 was a member of an aspartic protease family and phylogenetic analysis indicated that Sc-ASP155 was clustered with Sc-ASP113. In situ hybridization showed that sc-asp155 was expressed in subventral cells. Additionally, we determined that sc-asp155 is a single-copy gene in S. carpocapsae. Homology modeling showed that Sc-ASP155 adopts a typical aspartic protease structure. The up-regulated Sc-ASP155 expression revealed that this protease could play a role in the parasitic process. In this study, we have cloned the gene and determined the expression of the pepsin-like aspartic protease Sc-ASP155 in S. carpocapsae.

Systemic RNAi mediated gene silencing in the anhydrobiotic nematode Panagrolaimus superbus

BACKGROUND

Gene silencing by RNA interference (RNAi) is a powerful tool for functional genomics. Although RNAi was first described in Caenorhabditis elegans, several nematode species are unable to mount an RNAi response when exposed to exogenous double stranded RNA (dsRNA). These include the satellite model organisms Pristionchus pacificus and Oscheius tipulae. Available data also suggest that the RNAi pathway targeting exogenous dsRNA may not be fully functional in some animal parasitic nematodes. The genus Panagrolaimus contains bacterial feeding nematodes which occupy a diversity of niches ranging from polar, temperate and semi-arid soils to terrestrial mosses. Thus many Panagrolaimus species are adapted to tolerate freezing and desiccation and are excellent systems to study the molecular basis of environmental stress tolerance. We investigated whether Panagrolaimus is susceptible to RNAi to determine whether this nematode could be used in large scale RNAi studies in functional genomics.

RESULTS

We studied two species: Panagrolaimus sp. PS1159 and Panagrolaimus superbus. Both nematode species displayed embryonic lethal RNAi phenotypes following ingestion of Escherichia coli expressing dsRNA for the C. elegans embryonic lethal genes Ce-lmn-1 and Ce-ran-4. Embryonic lethal RNAi phenotypes were also obtained in both species upon ingestion of dsRNA for the Panagrolaimus genes ef1b and rps-2. Single nematode RT-PCR showed that a significant reduction in mRNA transcript levels occurred for the target ef1b and rps-2 genes in RNAi treated Panagrolaimus sp. 1159 nematodes. Visible RNAi phenotypes were also observed when P. superbus was exposed to dsRNA for structural genes encoding contractile proteins. All RNAi phenotypes were highly penetrant, particularly in P. superbus.

CONCLUSION

This demonstration that Panagrolaimus is amenable to RNAi by feeding will allow the development of high throughput methods of RNAi screening for P. superbus. This greatly enhances the utility of this nematode as a model system for the study of the molecular biology of anhydrobiosis and cryobiosis and as a possible satellite model nematode for comparative and functional genomics. Our data also identify another nematode infraorder which is amenable to RNAi and provide additional information on the diversity of RNAi phenotypes in nematodes.

Effect of several centrifugal pump passages on the viability and activity of Steinernema carpocapsae, a biopesticide

The effect of several passages through a centrifugal pump on the viability and activity of Steinernema corpocapsoe was investigated. A tendency of reduced viability was detected after 10 passages through the centrifugal pump, but the difference was not statistically significant. Activity decreased significantly from 91.9% to 83.6%. The experimental set-up was chosen to eliminate temperature increase. Therefore, the results prove that mechanical pump damage cannot be excluded as the cause of EPN damage during spray application.

Temperature effects on Korean entomopathogenic nematodes, Steinernema glaseri and S. longicaudum, and their symbiotic bacteria

We investigated the temperature effects on the virulence, development, reproduction, and motility of two Korean isolates of entomopathogenic nematodes, Steinernema glaseri Dongrae strain and S. longicaudum Nonsan strain. In addition, we studied the growth and virulence of their respective symbiotic bacterium, Xenorhabdus poinarii for S. glaseri and Xenorhabdus sp. for S. longicaudum, in an insect host at different temperatures. Insects infected with the nematode-bacterium complex or the symbiotic bacterium was placed at 13 degrees C, 18 degrees C, 24 degrees C, 30 degrees C, or 35 degrees C in the dark and the various parameters were monitored. Both nematode species caused mortality at all temperatures tested, with higher mortalities occurring at temperatures between 24 degrees C and 30 degrees C. However, S. longicaudum was better adapted to cold temperatures and caused higher mortality at 18 degrees C than S. glaseri. Both nematode species developed to adult at all temperatures, but no progeny production occurred at 13 degrees C or 35 degrees C. For S. glaseri, nematode progeny production was best at inocula levels above 20 infective juveniles/host at 24 degrees C and 30 degrees C, but for S. longicaudum, progeny production was generally better at 24 degrees C. Steinernema glaseri showed the greatest motility at 30 degrees C, whereas S. longicaudum showed good motility at 24 degrees C and 30 degrees C. Both bacterial species grew at all tested temperatures, but Xenorhabdus sp. was more virulent at low temperatures (13 degrees C and 18 degrees C) than X poinarii.

Monoxenic liquid culture of the entomopathogenic nematode Steinernema carpocapsae using a culture medium containing whey

The submerged culture of the entomopathogenic nematode Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila, was carried out in orbitally agitated bottles using a culture medium containing whey (in grams per litre: 500 whey, 20 yeast extract, 10 dried egg yolk-food grade, 3 sodium chloride, 37 corn oil-food grade). Maximum total viable nematode concentrations of 198,333ml(-1) were achieved within fermentations of 24 days with 64% of the nematode population within the infective juvenile stage (IJ) (126,666ml(-1)) at the end. The kinetics of the bioprocess was well modelled using the four-parameter Sigmoidal model and the corresponding maximum specific rates of nematode production (0.47 day(-1)), carbohydrates consumption (0.0008g(carbohydrates)g(nematodes)(-1)day(-1)) and nitrogen consumption (4.44g(nitrogen)g(nematodes)(-1)day(-1)) are first proposed. Besides, X. nematophila appears to have the capacity of lactose hydrolysis.

Acanthocytes of Stropharia rugosoannulata function as a nematode-attacking device

Efficient killing of nematodes by Stropharia rugosoannulata Farlow ex Murrill cultures was observed. This fungus showed the ability to immobilize the free-living nematode Panagrellus redivivus Goodey within minutes and to immobilize the pine wilt nematode Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle within hours on agar plates. Moreover, P. redivivus worms were completely degraded by the fungus within 24 to 48 h. The cultures of S. rugosoannulata studied shared the characteristic of abundantly producing cells with finger-like projections called acanthocytes. We showed that the nematode-attacking activity of this fungus is carried out by these spiny acanthocytes and that mechanical force is an important factor in the process. Furthermore, the growth and nematode-attacking activity of the fungus in soil were also determined, and our results suggest that acanthocytes are functional in soil.

Nutritive significance of crystalline inclusion proteins of Photorhabdus luminescens in Steinernema nematodes

Phase I cells of Photorhabdus luminescens produce two types of intracellular crystalline inclusion proteins designated CipA and CipB. The genes encoding CipA and CipB proteins from P. luminescens H06 were expressed respectively in Escherichia coli and these cells were used to feed the axenic first juveniles (J1) of three Steinernema nematode isolates in liquid cultures and on agar plates. In liquid cultures, the axenic J1 juveniles of all three test Steinernema nematode isolates were able to produce next dauer juveniles (DJs) in the E. coli cultures with at least one of the expressed Cip proteins, but unable to develop beyond the next J1 stage without expressed Cip proteins. For each target nematode isolate, addition of the supernatant of the bacterial culture of its Xenorhabdus symbiont to the tested liquid cultures did not induce the formation of DJs. However, on LB agar plates with different test E. coli cultures, all J1 juveniles of the three Steinernema strains finally developed into next DJs. It seemed that the metabolite pathway of the test bacteria in both culture systems was different. The presence of the Cip proteins has a significant influence on the DJ formation of the Steinernema nematodes in liquid culture system.

Unusual intestinal lamellae in the nematode Rhabditophanes sp. KR3021 (Nematoda: Alloinematidae)

The free-living nematode Rhabditophanes sp. has recently been placed in a clade of animal parasites and may be a unique example of a reversal to a nonparasitic lifestyle. Detailed morphological analysis of the intestine reveals the unusual and unique structure of splitting microlamellae forming a meshwork with cavities along the entire intestinal tract. Secretion vesicles were observed along the whole tract and along the length of the lamellae. It is suggested that these lamellae are adaptations to a different digestive strategy where low food availability and a low absorption surface are compensated for by maximizing the nutrient uptake efficiency along the entire length of the intestine. The likely reversal to a free-living life cycle may have caused drastic changes in diet, providing the necessary driving forces to such morphological changes.

daf-7 and the development of Strongyloides ratti and Parastrongyloides trichosuri

daf-7 is a key ligand in one of the three pathways that control dauer larva development in Caenorhabditis elegans. Given the similarities between dauer larvae of free-living nematodes and third stage infective larvae of animal parasitic nematodes, we hypothesised that daf-7 may be involved in the development of these infective larvae. To investigate this, we cloned daf-7 orthologues from Strongyloides ratti and Parastrongyloides trichosuri and analysed their RNA level by semi-quantitative RT-PCR during the S. ratti and P. trichosuri life cycles and in a range of in vitro and in vivo conditions. We found that, in both species, the RNA level of daf-7 was low in free-living stages but peaked in the infective L3 (iL3) stage with little or no expression in the parasitic stages. This contrasts with the daf-7 RNA level in C. elegans, which peaks in L1, decreases thereafter, and is absent in dauer larvae. The RNA level of daf-7 in infective larvae was reduced by larval penetration of host skin or development in the host, but not by a shift to the body temperature of the host.

Monoxenic production of the entomopathogenic nematode Steinernema carpocapsae using culture media containing agave juice (aguamiel) from Mexican maguey-pulquero (Agave spp). Effects of the contents of nitrogen, carbohydrates and fat on infective juvenile production

The production of infective juvenile stages (IJ) of the entomopathogenic nematode Steinernema carpocapsae in the presence of its symbiotic bacterium Xenorhabdus nematophilus was carried out in orbitally agitated bottles. Four complex culture media (M1-M4) were used, containing from 8% to 28% (by vol.) agave juice (aguamiel) from Mexican maguey-pulquero (Agave spp) as the main carbohydrate source. After 20 days of fermentation, a maximum viable IJ concentration of 249,000 IJ/ml and an initial nematode population multiplication factor of x620 were achieved when medium M4 was used (aguamiel concentration in this medium was 28% by vol.). M4 medium contained (w/v): 0.3% total nitrogen, 3.2% total carbohydrates and 3.0% total fat. According to the results obtained, total carbohydrates concentration appeared to be of great importance in obtaining high IJ concentrations.

Liquid culture mass production of biocontrol nematodes, Heterorhabditis bacteriophora (Nematoda: Rhabditida): improved timing of dauer juvenile inoculation

Heterorhabditis bacteriophora is used in biological control of soil-borne insect pests in horticulture and turf. Mass production is carried out in monoxenic liquid cultures pre-incubated with the symbiont of the nematodes, the bacterium Photorhabdus luminescens, before nematode dauer juveniles (DJ) are inoculated. As a response to bacterial food signals, the DJ recover from the developmentally arrested dauer stage, grow to adults and produce DJ offspring. Variable DJ recovery after inoculation into cultures of P. luminescens often causes process failure due to low numbers of adult nematodes in the medium. In order to enhance DJ recovery, improve nematode population management and increase yields, the optimal timing for DJ inoculation was sought. The process parameter pH and respiration quotient (RQ) were recorded in order to test whether changes can be used to identify the best moment for DJ inoculation. When DJ were inoculated during the lag and early logarithmic growth phases of P. luminescens cultures, DJ recovery was low and almost no nematode reproduction was obtained. High populations of P. luminescens phase variants were recorded. Recovery and yields increased when DJ were inoculated during the latter log phase during which the RQ dropped to values <0.8 and the pH reached a maximum. The highest DJ recovery and yields were observed in cultures that were inoculated during the late stationary growth phase. This period started with the increase of the pH after its distinct minimum at pH <8.0. Thus optimal timing for DJ inoculation can be defined through monitoring of the pH in the P. luminescens culture.

Development of a low-cost technology for mass production of the free-living nematode Panagrellus redivivus as an alternative live food for first feeding fish larvae

The free-living nematode Panagrellus redivivus is a suitable food source for first feeding fish. In the present report, a new method for the mass production of P. redivivus is presented. The technique involves multiplication of the nematode in monoxenic (single microorganism: Saccharomyces cerevisiae) solid culture (fluid media supported by 1- to 4-cm(3) sponge cubes) in autoclavable plastic bags (size range: 50 x 30 cm to 75 x 67 cm). Two growing media were tested: oat-meal medium (OM), which is an oat-based medium (16.7% oat-meal flour in 0.8% saline solution), and purified ingredient medium (PIM), a semi-synthetic medium (1.64% meat peptone, 0.94% yeast extract, 12.6% corn starch, 0.24% glucose, 1.48% sunflower oil, in 0.8% saline solution). The bags were inoculated with 350 nematodes/g medium. After an average period of 12 days (11-13 days) at 25 degrees C, the average yield (number of nematodes/g medium) was 241 x 10(3) for OM and 333 x 10(3) for PIM in 12-l bags (50 x 30 cm). The production scale has currently reached a bag volume of 50 l (75 x 67 cm); using PIM and the conditions described above, it was possible to harvest more than 1.3 x 10(9) nematodes/bag (291 x 10(3) nematodes/g medium). In PIM, when sun flower oil was replaced with the same amount of fish oil or cod liver oil, yields of 259 x 10(3) and 290 x 10(3) nematodes/g medium, respectively, were attained. The technology for mass production and formulation of P. redivivus should enable fish-hatchery operators to rely on a cheap, standardised, and permanently available live food product for first feeding fish larvae.

Dauer juvenile longevity and stress tolerance in natural populations of entomopathogenic nematodes: is there a relationship?

Qualitative and quantitative genetic analysis of life span in experimental adult animals predicts that resistance to stress and longevity are positively correlated, but such studies on field populations of animals are rare. We tested this hypothesis using dauer juveniles of 15 natural populations of the entomopathogenic nematode, Heterorhabditis bacteriophora, collected from diverse localities. Dauer juvenile longevity at 25 degrees C in autoclaved tap water and tolerance to major environmental stresses including heat (survival at 40 degrees C for 2 h), ultraviolet (UV) radiation (original virulence remaining after exposure to 302 nm UV for 5 min), hypoxia (survival at approximately 0% dissolved O2 at 25 degrees C for 96 h), and desiccation (survival in 25% glycerol at 25 degrees C for 72 h) differed significantly among populations. Intrinsic dauer juvenile longevity, defined as the number of weeks to 90% mortality (LT90) estimated using probit analysis of nematode survival data at 25 degrees C varied between 6 and 16 weeks among populations. Longevity was most strongly correlated with heat followed by UV and hypoxia tolerance, respectively, but showed no correlation with desiccation tolerance. The strong positive correlation of longevity with heat tolerance was further confirmed through principal components analysis which showed almost identical variance for heat and longevity. Among the stress factors, only UV tolerance was positively correlated with heat and hypoxia tolerance. Differences in longevity and stress tolerance in nematode populations isolated from a single 200 m2 grassland locality further support another hypothesis that population structure of heterorhabditid nematodes is highly fragmented, thus suggesting the existence of metapopulation dynamics.

Infection behavior of the rhabditid nematode Phasmarhabditis hermaphrodita to the grey garden slug Deroceras reticulatum

Infection behavior of the rhabditid nematode Phasmarhabditis hermaphrodita to the grey garden slug Deroceras reticulatum was studied. The dauer (enduring or nonaging) juveniles of P. hermaphrodita invade D. reticulatum within 8-16 hr following external exposure, with the posterior mantle region containing the shell cavity serving as the main portal of entry. The dauer juveniles can recover, multiply, and produce new dauer juveniles in the slug and slug feces homogenates, but not in the soil extract. These results demonstrate that P. hermaphrodita is a facultative parasite of the slug and can complete its life cycle under nonparasitic conditions associated with the host. Although the juvenile and adult nematodes can kill the slug if injected into the shell cavity of the host, only the dauer juvenile can serve as an infective stage in the natural environment.

Comparison of the Galleria baiting technique and a direct extraction method for recovering Steinernema (Nematoda: Rhabditida) infective-stage juveniles from soil

Forty soil samples from forests and other biotopes in Germany and the Czech Republic were studied for the presence of entomopathogenic nematodes using the Galleria bait method at the same time as a sieving-decanting method for direct extraction of infective-stage juveniles. Five Steinernema species were recovered from the samples from Germany and four species from the samples from Czechia. All five species were recovered with both methods, but the baiting technique was generally less effective and mixtures of species were frequently undetected. The direct extraction method provided quantitative estimates of infective-stage juvenile density but no information on their infectivity or on morphological characters of adults, and nematode cultures could not be established.

Effect of airflow rate on yields of Steinernema carpocapse Az 20 in liquid culture in an external-loop airlift bioreactor

Maximization of the contact between males and females is a key factor in the production of the nematode Steinernema carpocapsae in a bioreactor.%The influence of the airflow rate in male and female distribution and mass production in an external-loop bioreactor with a deceleration zone was studied. When operating at an airflow rate of 0.05 vvm, a high retention of females in the deceleration zone of the bioreactor was observed and a larger nematode productivity was obtained. At this aeration rate there was a higher proportion of males in that zone, which together with the lower circulation rate, increases the probability of encounters, thereby explaining the increase in productivity.

Liquid media development for Heterorhabditis bacteriophora: lipid source and concentration

Lipids are important entomopathogenic nematode nutritional components because they are energy reserves and serve as indicators of nematode quality. The composition and concentration of the media lipid component determine bacterial and nematode yields. Heterorhabditis bacteriophora and its symbiont, Photorhabdus luminescens, were cultured in media containing various lipid sources. As lipid concentration increased from 2.5% to 8.0% (w/v), the final yield and productivity [calculated from the number of infective juveniles (IJ)] increased significantly from 2.1 x 10(5) IJ ml(-1) to 2.8 x 10(5) IJ ml(-1) (P < 0.05) and from 8.9 x 10(5) IJ l(-1) day(-1) to 11.8 x 10(5) IJ l(-1) day(-1) (P < 0.05), respectively. The nematode yield coefficient (IJ per gram of media), however, decreased from 2.8 x 10(6) to 2.2 x 10(6) (P < 0.05), while recovery increased from 45.3% to 58.0% (P < 0.05). Bacterial cell mass remained constant at 4.6 mg ml(-1) with changing lipid content (P > 0.05). The largest nematode yield (2.8 x 10(5) IJ ml(-1)) was achieved within 8 days, using a medium containing an 8% (w/v) olive and canola oil (50:50 w/v) combination. Moreover, developmental synchrony was achieved in this medium with 96% infective juveniles. In short, lipid sources rich in mono-unsaturated fatty acids and poor in saturated fatty acids produced optimal nematode growth.

Using deuterium as an isotopic tracer to study the energy metabolism of infective juveniles of Steinernema carpocapsae under aerobic conditions

Changes in survival, mean dry weight, levels of key energy reserve compounds and respiration of non-feeding infective juveniles (IJs) of Steinernema carpocapsae incubated in various ratios of D2O/H2O on a shaker at 28 degrees C were determined. Patterns of deuterium distribution in trehalose, glycogen and key fatty acids of the IJs incubated in 50% (v/v) D2O/H2O were also examined. The rates of decline in mean dry weight and lipid levels of IJs incubated in D2O/H2O were proportional, while the survival times of IJs were inversely proportional, to the ratio of D2O/H2O. Deuterium was randomly and extensively incorporated into the C-H bonds of trehalose and glycogen but was barely incorporated in fatty acid moieties of the IJs. The changes in the patterns and the extents of deuterium incorporation, as well as the levels of trehalose, glycogens and fatty acids during the experimental period indicate that: (1) The lipogenesis pathway is not functioning in the Ijs. (2) Trehalose and glycogen are constantly consumed and replenished and they are mainly derived from lipids. (3) Futile cycles involving trehalose and glycogen, which enable IJs to regulate the levels of these two compounds more effectively, may exist. The results support the view that lipids are the primary energy reserve of the IJs while trehalose, glycogen and proteins can be used for energy generation, even though this is not their primary role.

Anhydrobiotic potential and long-term storage of entomopathogenic nematodes (Rhabditida: Steinernematidae)

Anhydrobiosis is considered to be an important means of achieving storage stability of entomopathogenic nematodes that are used in biological control. This study explored the effects of anhydrobiosis on longevity and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes Steinernema carpocapsae, Steinernema feltiae, and Steinernema riobrave at 5 and 25 degrees C. Anhydrobiosis was induced in water-dispersible granules (WG) at 0.966-0.971 water activity and 25 degrees C following a 7-day preconditioning of IJs at 5 degrees C in tap water. Survival and infectivity of the desiccated (anhydrobiotic) IJs was compared with non-desiccated IJs stored in water for different periods. Anhydrobiosis increased longevity of S. carpocapsae IJs by 3 months and of S. riobrave by 1 month in WG at 25 degrees C as compared with IJs stored in water. However, desiccation decreased S. feltiae longevity at 25 degrees C and of all three species at 5 degrees C. These results demonstrate a shelf-life of 5 months for S. carpocapsae at 25 degrees C and 9 months at 5 degrees C in WG with over 90% IJ survival. For S. feltiae, over 90% survival occurred only for 2 months at 25 degrees C and 5 months at 5 degrees C in WG. Steinernema riobrave had over 90% survival only for 1 month at 25 degrees C and the survival dropped below 85% within 1 month at 5 degrees C. Induction of anhydrobiosis in WG resulted in 85, 79 and 76% reduction in oxygen consumption by S. carpocapsae, S. feltiae, and S. riobrave IJs, respectively. Differences in IJ longevity among three species in water at 25 degrees C were related both to the initial lipid content and the rate of lipid utilisation, but not at 5 degrees C. The one-on-one infection bioassays indicated that desiccation had no negative effect on the infectivity of any of the nematode species suggesting no harmful effect on the IJs and/or their symbiotic bacteria. The species differences in IJ longevity and desiccation survival at different temperatures are discussed in relation to their foraging strategy and temperature adaptation.

Buccal capsule development as a consideration for phylogenetic analysis of Rhabditida (Nemata)

Bacterial feeding nematodes in the order Rhabditida including Zeldia punctata (Cephalobidae) and Caenorhabditis elegans (Rhabditidae) differ profoundly in the buccal capsule parts and associated cells. We carried out a range of tests to determine which buccal capsule parts and cells are evolutionarily homologous between the representative species of the two families. Tests included reconstruction of the buccal capsule and procorpus with transmission electron microscopy (TEM), nuclei position and morphology using 4, 6-diamidino-2-phenylindole (DAPI) staining, and cell lineage using four dimensional (4D) microscopy. The lining of the buccal capsule of Z. punctata and additional Cephalobidae includes four sets of muscular radial cells, ma, mb, mc and md, in contrast to C. elegans and additional Rhabditidae, which has two sets of epithelial cells (e1, e3) and two sets of muscle cells (m1, m2). Cell lineage of a nematode closely related to Z. punctata, Cephalobus cubaensis, supports the hypothesis that in cephalobids the e1 and e3 cells become hypodermal cells or are programmed to die. Our findings contradict all previous hypotheses of buccal capsule homology, and suggest instead that ma and mb in Z. punctata are homologous to m1 and m2 in C. elegans respectively. We also hypothesize that ma and mb could be homologous to primary and secondary sets of stylet-protractor muscle cells in the plant parasitic Tylenchida.

The ultrastructure of the cuticle and sheath of infective juveniles of entomopathogenic steinernematid nematodes

The ultrastructure of the cuticle of infective juveniles (IJs) of Steinernema carpocapsae (newly emerged and 80-day-old) and newly emerged IJs of S. riobravis, S. feltiae and S. glaseri was examined using transmission electron microscopy. The thickness of four distinctive layers of the cuticle was measured: epicuticle, cortical and median layer, striated layer and fibrous mat. The thickness of the cuticle was correlated with the size of the IJ. In the case of newly emerged IJs, the smallest species, S. carpocapsae, had a cuticle thickness of c. 270 nm compared with c. 460 nm for S. glaseri, the largest of the four species. The overall thickness of the cuticle or the thickness of the cuticle layers was not correlated with the ability of the IJs of the four species to survive desiccation per se. The major difference between newly emerged IJs of the four species was that S. carpocapsae had a proportionately thicker striated layer compared with the other three species. The significance of this is not known but it may be an adaptation involving the nictation behaviour of this species. A substantial change was observed in the cuticle of aged (80-day-old) IJs of S. carpocapsae, whereby the thickness of the cortical and median layer increased by more than 100% and the overall thickness of the cuticle increased by about 50%. Two possible explanations for this increase are: (i) new material was synthesized; or (ii) the fluid content of this layer increased due to an increase in the permeability of the outer layers of the cuticle. The ultrastructure of the sheaths of S. feltiae and S. glaseri was also examined and, apart from S. glaseri having a thicker sheath, the structure of the sheath in both species was similar, with the epicuticle and striated layer still visible.

Insertional inactivation of genes encoding the crystalline inclusion proteins of Photorhabdus luminescens results in mutants with pleiotropic phenotypes

The entomopathogenic bacterium Photorhabdus luminescens exhibits phase variation when cultured in vitro. The variant forms of P. luminescens are pleiotropic and are designated phase I and phase II variants. One of the characteristic phenotypes of phase I cells is the production of two types of intracellular protein inclusions. The genes encoding the protein monomers that form these inclusions, designated cipA and cipB, were cloned and characterized. cipA and cipB encode hydrophobic proteins of 11,648 and 11,308 Da, respectively. The deduced amino acid sequences of CipA and CipB have no significant amino acid sequence similarity to any other known protein but have 25% identity and 49% similarity to each other. Insertional inactivation of cipA or cipB in phase I cells of P. luminescens produced mutants that differ from phase I cells in bioluminescence, the pattern and activities of extracellular products, biochemical traits, adsorption of dyes, and ability to support nematode growth and reproduction. In general, the cip mutants were phenotypically more similar to each other than to either phase I or phase II variants.

An evolutionary framework for the study of developmental evolution in a set of nematodes related to Caenorhabditis elegans

Nematodes are known to be a useful system for studies of comparative development. Here we perform a molecular phylogenetic analysis to allow for the independent interpretation of the developmental and morphological changes observed among a selected set of nematode species. Our molecular phylogenetic analysis is based on coding regions of the genes for RNA polymerase II, the small subunit rRNA and an expansion segment of the large subunit rRNA. Sequences were compared from five species in the family (Rhabditidae) that includes the developmental model organism Caenorhabditis elegans and from an outgroup taxon Aduncospiculum halicti (Diplogasterina). The phylogenetic analysis does not support the monophyly of the subfamily Mesorhabditinae and identifies the unnamed strain PS1010 as a sister taxon of C. elegans despite its morphologically divergent buccal capsule. On the basis of the inferred framework, we can begin to interpret the evolution of vulval development and of morphological differences among these nematode species.

Evolution of male tail development in rhabditid nematodes related to Caenorhabditis elegans

The evolutionary pathway that has led to male tails of diverse morphology among species of the nematode family Rhabditidae was reconstructed. This family includes the well-studied model species Caenorhabditis elegans. By relating the steps of male tail morphological evolution to the phenotypic changes brought about by developmental mutations induced experimentally in C. elegans, the goal is to identify genes responsible for morphological evolution. The varying morphological characters of the male tails of several rhabiditid species have been described previously (Fitch and Emmons, 1995, Dev. Biol. 170:564-582). The developmental events preceding differentiation of the adult structures have also been analyzed; in many cases the origins of varying adult morphological characters were traced to differences during ontogeny. In the present work, the evolutionary changes producing these differences were reconstructed in the context of the four possible phylogenies supported independently by sequences of 18S ribosomal RNA genes (rDNA). Two or more alternative states were defined for 36 developmental and adult morphological characters. These characters alone do not provide sufficient data to resolve most species relationships; however, when combined with the rDNA characters, they provide stronger support for one of the four rDNA phylogenies. Assuming a model of ordered transformations for multistate developmental characters generally results in greater resolution. Transformations between character states can be assigned unequivocally by parsimony to unambiguous branches for most of the characters. Correlations are thereby revealed for some of the developmental characters, indicating a probability of a shared developmental or genetic regulatory pathway. Four of the unequivocal character state changes on unambiguously supported branches closely resemble the phenotypic changes brought about by known mutations in C. elegans. These mutations define genes that are known to act in genetic regulatory hierarchies controlling pattern formation, differentiation, and morphogenesis. Although these studies are still at an early stage, these results strongly suggest that parallel studies of developmental mutants in C. elegans and of morphological and developmental evolution among related nematodes will help define genetic changes underlying the evolution of form.

Evolution of cell lineage and pattern formation in the vulval equivalence group of rhabditid nematodes

During the formation of the vulva in many nematode hermaphrodites or females, pattern formation, induction, and cell specification can readily be studied at a single-cell level. Nematodes thus allow an evolutionary analysis of developmental processes. We have analyzed cell lineages and pattern formation in the vulva equivalence group of six rhabditid nematodes of the genera Oscheius, Rhabditella, Rhabditoides, Pelodera, and Protorhabditis. The comparison of these species with four previously analyzed species of this family reveals evolutionary modification at several levels. The number of vulva precursor cells (VPCs) differ among species. Of the three particular cell lineages (1 degree, 2 degrees, and 3 degrees) generated by the vulva precursor cells in Caenorhabditis, two (2 degrees and 3 degrees) are altered, whereas the third lineage (1 degree) is conserved among the analyzed species. While most vulval lineages are invariant, we observe variability of the 3 degrees lineage in Pelodera with respect to the number of precursor cells adopting this fate and the number of progeny formed. In two species, the 3 degrees lineage generates an asymmetrical set of cells, oriented by the gonad. In Protorhabditis we frequently find animals with an additional or altered set of VPCs forming vulval tissue.