Endophytic Beauveria bassiana increases galling of 'Rutgers' tomato roots with Meloidogyne incognita

Beauveria bassiana is endophytic in many plant species and has been shown to protect host plants against insect pests and plant pathogens. However, less is known about its activity against plant-parasitic nematodes. In vitro and plant assays were conducted to determine the effect of B. bassiana 11-98 (Bb) on Meloidogyne incognita (root-knot nematode; RKN). Beauveria bassiana was confirmed as an endophyte in ‘Rutgers’ tomato and colonization patterns of Bb in ‘Rutgers’ (highly susceptible to RKN) were compared with those in ‘Mountain Spring’ (less susceptible to RKN). In greenhouse tests with ‘Rutgers’ at 30 and 60 days after treatment (DAT) with RKN and Bb, there were few differences in plant growth variables among treatments in repeated trials. However, RKN root galling and egg count/root system were enhanced in plants treated with Bb at 60 DAT. In an in vitro assay with egg masses from greenhouse tests, the percentages of hatched eggs, and mobile and immobile nematodes did not differ significantly for RKN and RKN+Bb treatments. The presence of viable Bb from roots was confirmed by collecting egg suspensions from root galls and plating them on selective medium. Colonies of Bb were verified on agar medium, but no parasitism of RKN eggs was observed. Research is needed to investigate factors responsible for increased galling by RKN in the presence of endophytic Bb in ‘Rutgers’ tomato.

Soil indigenous microbiome and plant genotypes cooperatively modify soybean rhizosphere microbiome assembly

BACKGROUND

Plants have evolved intimate interactions with soil microbes for a range of beneficial functions including nutrient acquisition, pathogen resistance and stress tolerance. Further understanding of this system is a promising way to advance sustainable agriculture by exploiting the versatile benefits offered by the plant microbiome. The rhizosphere is the interface between plant and soil, and functions as the first step of plant defense and root microbiome recruitment. It features a specialized microbial community, intensive microbe-plant and microbe-microbe interactions, and complex signal communication. To decipher the rhizosphere microbiome assembly of soybean (Glycine max), we comprehensively characterized the soybean rhizosphere microbial community using 16S rRNA gene sequencing and evaluated the structuring influence from both host genotype and soil source.

RESULTS

Comparison of the soybean rhizosphere to bulk soil revealed significantly different microbiome composition, microbe-microbe interactions and metabolic capacity. Soil type and soybean genotype cooperatively modulated microbiome assembly with soil type predominantly shaping rhizosphere microbiome assembly while host genotype slightly tuned this recruitment process. The undomesticated progenitor species, Glycine soja, had higher rhizosphere diversity in both soil types tested in comparison to the domesticated soybean genotypes. Rhizobium, Novosphingobium, Phenylobacterium, Streptomyces, Nocardioides, etc. were robustly enriched in soybean rhizosphere irrespective of the soil tested. Co-occurrence network analysis revealed dominant soil type effects and genotype specific preferences for key microbe-microbe interactions. Functional prediction results demonstrated converged metabolic capacity in the soybean rhizosphere between soil types and among genotypes, with pathways related to xenobiotic degradation, plant-microbe interactions and nutrient transport being greatly enriched in the rhizosphere.

CONCLUSION

This comprehensive comparison of the soybean microbiome between soil types and genotypes expands our understanding of rhizosphere microbe assembly in general and provides foundational information for soybean as a legume crop for this assembly process. The cooperative modulating role of the soil type and host genotype emphasizes the importance of integrated consideration of soil condition and plant genetic variability for future development and application of synthetic microbiomes. Additionally, the detection of the tuning role by soybean genotype in rhizosphere microbiome assembly provides a promising way for future breeding programs to integrate host traits participating in beneficial microbiota assembly.

Agricultural intensification and urbanization negatively impact soil nematode richness and abundance: a meta-analysis

Human activity has extensively transformed the land surface by agricultural intensification and urbanization. In soil, nematodes are the most abundant invertebrates. The effect of human interventions was assessed on overall richness, overall abundance, richness and abundance of nematodes of each trophic group and colonizer-persister (c-p) guild by comparing urban, agriculture and disturbed grassland (DGL) with natural grassland (NGL) and forest ecosystems. Meta-analyses were conducted to generate quantitative summaries from 111 published articles that met the inclusion criteria, 91 expressed data in grams and 20 expressed data in cm³. Results from data expressed per 100 g of soil indicated that overall richness was higher in forest than in NGL, DGL, urban, and agriculture ecosystems. The richness of all c-p guilds and of all trophic groups except herbivores was highest in forest ecosystems. In contrast, overall abundance was highest in DGL, agriculture and forest ecosystems. The abundance of c-p 1, c-p 2 and c-p 3 guilds and bacterivores, fungivores and herbivores was highest in disturbed ecosystems, while the abundance of c-p 4 and c-p 5 guilds and predators and omnivores was highest in relatively undisturbed ecosystems. Results from data expressed as nematodes per 100 cm³ of soil indicated that abundance followed a similar pattern, but richness often differed between the two methodologies. These meta-analyses strengthen the concept that human interventions adversely impact both richness and abundance using nematodes as soil health bioindicators.

Human activity has extensively transformed the land surface by agricultural intensification and urbanization. In soil, nematodes are the most abundant invertebrates. The effect of human interventions was assessed on overall richness, overall abundance, richness and abundance of nematodes of each trophic group and colonizer-persister (c-p) guild by comparing urban, agriculture and disturbed grassland (DGL) with natural grassland (NGL) and forest ecosystems. Meta-analyses were conducted to generate quantitative summaries from 111 published articles that met the inclusion criteria, 91 expressed data in grams and 20 expressed data in cm³. Results from data expressed per 100 g of soil indicated that overall richness was higher in forest than in NGL, DGL, urban, and agriculture ecosystems. The richness of all c-p guilds and of all trophic groups except herbivores was highest in forest ecosystems. In contrast, overall abundance was highest in DGL, agriculture and forest ecosystems. The abundance of c-p 1, c-p 2 and c-p 3 guilds and bacterivores, fungivores and herbivores was highest in disturbed ecosystems, while the abundance of c-p 4 and c-p 5 guilds and predators and omnivores was highest in relatively undisturbed ecosystems. Results from data expressed as nematodes per 100 cm³ of soil indicated that abundance followed a similar pattern, but richness often differed between the two methodologies. These meta-analyses strengthen the concept that human interventions adversely impact both richness and abundance using nematodes as soil health bioindicators.

Effects of plant and animal waste-based compost amendments on the soil food web, soil properties, and yield and quality of fresh market and processing carrot cultivars

A substantial knowledge gap exists on how compost source and rate of application affect nematode community-based soil food web structure, soil health, soil physiochemistry, and crop yield and quality in short- and full-season crops. We tested effects of plant (PC)- and animal (AC)-based compost at 1, 1.5 and 2× the standard nitrogen (N) rate on processing carrot ‘Cupar’ and fresh market ‘Sugarsnax 54’ (short-season crop) over 2-3 growing seasons. Low abundance of nematodes and domination of herbivores and bacterivores indicate that the field is biologically stressed. While outcomes of most measured parameters varied by compost source and/or rate, an increase in soil food web structure with time was most consistent. A combination of the variable outcomes and correlation patterns suggest that a multifactor analysis may best quantify compost-driven changes in soil ecosystems as opposed to looking for changes in a single parameter.

Comparative Analysis of Xenorhabdus koppenhoeferi Gene Expression during Symbiotic Persistence in the Host Nematode

Species of Xenorhabdus and Photorhabdus bacteria form mutualistic associations with Steinernema and Heterorhabditis nematodes, respectively and serve as model systems for studying microbe-animal symbioses. Here, we profiled gene expression of Xenorhabdus koppenhoeferi during their symbiotic persistence in the newly formed infective juveniles of the host nematode Steinernema scarabaei through the selective capture of transcribed sequences (SCOTS). The obtained gene expression profile was then compared with other nematode-bacteria partnerships represented by Steinernema carpocapsae-Xenorhabdus nematophila and Heterorhabditis bacteriophora-Photorhabdus temperata. A total of 29 distinct genes were identified to be up-regulated and 53 were down-regulated in X. koppenhoeferi while in S. scarabaei infective juveniles. Of the identified genes, 8 of the up-regulated and 14 of the down-regulated genes were similarly expressed in X. nematophila during persistence in its host nematode S. carpocapsae. However, only one from each of these up- and down-regulated genes was common to the mutualistic partnership between the bacterium P. temperata and the nematode H. bacteriophora. Interactive network analysis of the shared genes between X. koppenhoeferi and X. nematophila demonstrated that the up-regulated genes were mainly involved in bacterial survival and the down-regulated genes were more related to bacterial virulence and active growth. Disruption of two selected genes pta (coding phosphotransacetylase) and acnB (coding aconitate hydratase) in X. nematophila with shared expression signature with X. koppenhoeferi confirmed that these genes are important for bacterial persistence in the nematode host. The results of our comparative analyses show that the two Xenorhabdus species share a little more than a quarter of the transcriptional mechanisms during persistence in their nematode hosts but these features are quite different from those used by P. temperata bacteria in their nematode host H. bacteriophora.

Enhancing plant productivity while suppressing biofilm growth in a windowfarm system using beneficial bacteria and ultraviolet irradiation

Common problems in a windowfarm system (a vertical and indoor hydroponic system) are phytopathogen infections in plants and excessive buildup of biofilms. The objectives of this study were (i) to promote plant health by making plants more resistant to infection by using beneficial biosurfactant-producing Pseudomonas chlororaphis around the roots and (ii) to minimize biofilm buildup by ultraviolet (UV) irradiation of the water reservoir, thereby extending the lifespan of the whole system with minimal maintenance. Pseudomonas chlororaphis-treated lettuce grew significantly better than nontreated lettuce, as indicated by enhancement of color, mass, length, and number of leaves per head (p < 0.05). The death rate of the lettuce was reduced by ∼ 50% when the lettuce was treated with P. chlororaphis. UV irradiation reduced the bacteria (4 log reduction) and algae (4 log reduction) in the water reservoirs and water tubing systems. Introduction of P. chlororaphis into the system promoted plant growth and reduced damage caused by the plant pathogen Pythium ultimum. UV irradiation of the water reservoir reduced algal and biofilm growth and extended the lifespan of the system.

Ambush foraging entomopathogenic nematodes employ 'sprinters' for long-distance dispersal in the absence of hosts

Ambush foragers must employ a long-distance dispersal strategy to maximize reproductive success in the absence of hosts. This hypothesis was tested by comparing lateral dispersal of the ambusher, Steinernema carpocapsae , and the cruiser, Heterorhabditis bacteriophora , nematodes from infected host cadavers in autoclaved, silt-loam soil in large microcosms (0.05-1.5 m(2)) with or without vegetation in the absence of hosts. Dispersal was estimated by taking soil cores (5 × 2 cm in diameter) from the microcosms at different intervals (6-240 hr) and distances (3.8-61 cm) from the infected host cadavers and baiting with Galleria mellonella larvae. The numbers of baited larvae killed and the numbers of infective juveniles (IJs) penetrated in dead baits were counted to compute the percentage of IJs dispersed from the source cadavers, based on the emergence potential and penetration efficiency of the 2 species, and analyzed. Vegetation enhanced dispersal of both species but more so for H. bacteriophora . Although the pattern of dispersal differed spatio-temporally for the 2 species, average population displacement was similar (∼6 cm/day). A majority of the S. carpocapsae population ambushed close to the source cadaver (<3.8 cm), whereas a majority of H. bacteriophora population dispersed between 7-12 cm away from the source cadaver. About 4% of the S. carpocapsae population dispersed faster than the fastest H. bacteriophora , reaching 30-61 cm, compared to only 2% of the H. bacteriophora population dispersing this far. This use of 'sprinters' for long-distance dispersal may represent an adaptive dispersal strategy by the otherwise ambush forager S. carpocapsae in the absence of hosts.

Host recognition by entomopathogenic nematodes: Behavioral response to contact with host feces

Host recognition by entomopathogenic nematodes may occur through contact with insects' excretory products, cuticle, or gut contents. We analyzed the behavioral responses of four species of entomopathogenic nematodes during contact with feces of natural or experimental hosts. Host recognition by nematodes was manifested in alterations in the frequency and/or duration of one or more search parameters including forward crawling, headwaving, body-waving, stopping, backward crawling, head-rubbing, and headthrusting.Heterorhabditis bacteriophora andSteinernema glaseri showed behavioral responses to contact with feces of their natural hosts,Spodoptera exigua (Lepidoptera) andPopillia japonica (Coleoptera), and to the experimental hosts,Acheata domesticus (Orthoptera) andBlatella germanica (Blatteria).Steinernema carpocapsae responded only toB. germanica feces, whereas5. scapterisci did not significantly respond to any of the insect species. During contact with cockroach feces, all nematodes, exceptS. scapterisci, showed avoidance behavior. We suggest that ammonia present in cockroach feces is inhibitory to nematodes. Specific host recognition by entomopathogenic nematodes may be an important mechanism to maintain host affinities.

A lover and a fighter: the genome sequence of an entomopathogenic nematode Heterorhabditis bacteriophora

Heterorhabditis bacteriophora are entomopathogenic nematodes that have evolved a mutualism with Photorhabdus luminescens bacteria to function as highly virulent insect pathogens. The nematode provides a safe harbor for intestinal symbionts in soil and delivers the symbiotic bacteria into the insect blood. The symbiont provides virulence and toxins, metabolites essential for nematode reproduction, and antibiotic preservation of the insect cadaver. Approximately half of the 21,250 putative protein coding genes identified in the 77 Mbp high quality draft H. bacteriophora genome sequence were novel proteins of unknown function lacking homologs in Caenorhabditis elegans or any other sequenced organisms. Similarly, 317 of the 603 predicted secreted proteins are novel with unknown function in addition to 19 putative peptidases, 9 peptidase inhibitors and 7 C-type lectins that may function in interactions with insect hosts or bacterial symbionts. The 134 proteins contained mariner transposase domains, of which there are none in C. elegans, suggesting an invasion and expansion of mariner transposons in H. bacteriophora. Fewer Kyoto Encyclopedia of Genes and Genomes Orthologies in almost all metabolic categories were detected in the genome compared with 9 other sequenced nematode genomes, which may reflect dependence on the symbiont or insect host for these functions. The H. bacteriophora genome sequence will greatly facilitate genetics, genomics and evolutionary studies to gain fundamental knowledge of nematode parasitism and mutualism. It also elevates the utility of H. bacteriophora as a bridge species between vertebrate parasitic nematodes and the C. elegans model.

Homeowner attitudes and practices towards residential landscape management in Ohio, USA

This study describes the results of a survey of 432 homeowners in Ohio, USA concerning their perceptions and practices regarding management of residential landscapes. The results reveal that outdoor residential environments are extremely important to homeowners, who tend to view their yards as serving multiple functions: a place to observe nature and to socialize as well as a place of beauty and recreation. Use of a lawn care company to apply chemicals is reported by 22 % of respondents, while 40 % either apply chemicals themselves or have someone other than a lawn care company do it. Logistic regressions reveal that factors influencing a homeowner's decision to employ a lawn care company or to apply chemicals themselves include: household income (+), perceived impacts on the environment (-), whether the next door neighbor does it (+), and type of residential environment (rural -, suburban and urban +). A theme that emerges throughout the study is the perceived importance of the role of the lawn in residents' sense of social status or acceptance in the neighborhood. This perception can be viewed as a positive in ensuring that residential environments are well maintained, but also as a negative resulting in environmental degradation or presenting a barrier to creativity in the development of alternative residential environments. Specific policy implications of these findings are that efforts aimed at educating homeowners about the environmental impacts of their lawn care choices are likely to have more success if they are directed at neighborhood groups rather than individuals, show that alternatives are easy to adopt, affordable, and can produce the characteristics of lawns that homeowners seek.

History of entomopathogenic nematology

The history of entomopathogenic nematology is briefly reviewed. Topic selections include early descriptions of members of Steinernema and Heterorhabditis, how only morphology was originally used to distinguish between the species; descriptions of the symbiotic bacteria and elucidating their role in the nematode- insect complex, including antibiotic properties, phase variants, and impeding host defense responses. Other topics include early solutions regarding production, storage, field applications and the first commercial sales of entomopathogenic nematodes in North America. Later studies centered on how the nematodes locate insect hosts, their effects on non-target organisms and susceptibility of the infective juveniles to soil microbes. While the goals of early workers was to increase the efficacy of entomopathogenic nematodes for pest control, the increasing use of Heterorhabditis and Photorhabdus as genetic models in molecular biology is noted.

Differences in Immune Defense Evasion of Selected Inbred Lines of Heterorhabditis Bacteriophora in Two White Grub Species

We determined virulence of seven Heterorhabditis bacteriophora strain GPS11 inbred lines possessing superior infective juvenile longevity, and heat and ultra violet radiation tolerance against white grubs Popillia japonica and Cyclocephala borealis. At 1 and 2 weeks after treatment, inbred line A2 was significantly more virulent towards P. japonica compared to the parent strain GPS11 and inbred lines A7, A8, A12 and A21; and line A2 caused significantly higher C. borealis mortality than lines A6 and A12. Penetration, encapsulation and survival of two inbred lines, A2 and A12, that showed the highest and lowest virulence against both grub species were then assessed. There were no differences between the two lines for the total number of nematodes penetrated in either P. japonica or C. borealis within the first 24 h, but a significantly higher percentage of penetrated nematodes were alive in line A2 compared to the line A12 in both grub species. P. japonica immune response over time to hemocoel-injected nematodes of A2, A12 and the parent strain was further investigated. While all injected nematodes were encapsulated at 6 h post injection, non-encapsulated living nematodes were detected at 12 and 24 h post injection, showing the breakage out of encapsulation. A higher percentage of non-encapsulated living nematodes and a lower percentage of dead nematodes were found in line A2 as compared to the line A12 after 12 h post injection. These data suggest that virulence differences in the studied H. bacteriophora inbred lines are not due to differences in nematode penetration or recognition by the grub immune system, but are related to the ability of the infective juveniles to break out of encapsulation.

Comparative study of differential gene expression in closely related bacterial species by comparative hybridization

The ability to profile bacterial gene expression has markedly advanced the capacity to understand the molecular mechanisms of pathogenesis, epidemiology, and therapeutics. This advance has been coupled with the development of techniques that enable investigators to identify bacterial specifically expressed genes and promise to open new avenues of functional genomics by allowing researchers to focus on the identified differentially expressed genes. During the past two decades, a number of approaches have been developed to investigate bacterial genes differentially expressed in response to the changing environment, particularly during interaction with their hosts. The most commonly used techniques include in vivo expression technology, signature-tagged mutagenesis, differential fluorescence induction, and cDNA microarrays, which fall into two broad classes: mutagenesis-based technologies and hybridization-based technologies. Selective capture of transcribed sequences, a recently emerging method, is a hybridization-based technique. This technique is powerful in analyzing differential gene expression of the bacteria, with the superb ability to investigate the bacterial species with unknown genomic information. Herein, we describe the application of this technique in a comparative study of the gene expression between two closely related bacteria induced or repressed under a variety of conditions.

Susceptibility of the Adult Japanese Beetle, Popillia japonica to Entomopathogenic Nematodes

To build upon prior research demonstrating the potential of entomopathogenic nematode dissemination by infected adult Japanese beetle, Popillia japonica, we evaluated susceptibility of the adult beetles to 20 strains of Steinernema and Heterorhabditis under laboratory conditions. The nematodes were applied at a rate of 10,000 infective juveniles per 10 adult beetles in 148 mL plastic cups containing autoclaved sand and sassafras leaves as a source of food for the beetles. All strains infected the beetles and caused 55% to 95% mortality. The most virulent strains that caused 50% beetle mortality in less than 5 days included a strain of H. georgiana (D61), three strains of Steinernema sp. (R54, R45, and FC48), and two strains of S. carpocapsae (All and D60). The ability of two strains of Steinernema sp. (R45 and R54) and two strains of Heterorhabditis bacteriophora (D98 and GPS11) to infect and reproduce in the beetle was further examined to assess the potential of infected beetles to disseminate nematodes upon their death. All four strains infected and killed the beetles, but only Steinernema strains reproduced in the cadavers. We conclude that both Heterorhabditis and Steinernema strains are able to cause mortality to adult Japanese beetle, but Steinernema strains may be effectively disseminated due to their reproduction in the beetle.

purL gene expression affects biofilm formation and symbiotic persistence of Photorhabdus temperata in the nematode Heterorhabditis bacteriophora

Extensive studies of the well-known legume and rhizobium symbiosis model system suggest that the purine metabolic pathway plays a key role in microbe-plant interactions, although the exact mechanism is unknown. Here, we report the impact of a key purine metabolic gene, purL, on the symbiotic interaction between the bacterium Photorhabdus temperata and its nematode partner Heterorhabditis bacteriophora. Real-time PCR assays showed that the purL gene was upregulated in P. temperata in the nematode infective juvenile compared with artificial media. Mutation of the purL gene by in-frame deletion dramatically decreased the capacity of the bacterium to persist in infective juveniles and its ability to form biofilm in vitro. It was further demonstrated that purL gene expression was positively related to bacterial biofilm formation and the symbiotic persistence of the bacterium in nematode infective juveniles. A ΔpurL mutant lost the ability to support infective juvenile formation in the media which weakly supported biofilm formation, suggesting that a critical level of biofilm formation is required by the bacteria to support infective juvenile formation and thus establish their partnership. In addition, the defects in both biofilm formation and symbiotic ability due to the disruption of the purL gene could be partially restored by the addition of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an intermediate of the purine biosynthesis pathway. Overall, these data indicate that the purine metabolic pathway is important in microbe-animal symbioses, and that it may influence symbiotic interactions at the level of biofilm formation.

Phylogenetic and cophylogenetic relationships of entomopathogenic nematodes (Heterorhabditis: Rhabditida) and their symbiotic bacteria (Photorhabdus: Enterobacteriaceae)

Mutualistic association between entomopathogenic Photorhabdus bacteria and Heterorhabditis nematodes represents one of the emerging model systems in symbiosis studies, yet little is known about this partnership from a coevolutionary perspective. Herein, we investigated phylogenetic and cophylogenetic relationships of Heterorhabditis and Photorhabdus strains using molecular markers Internal Transcribed Spacer and gyrase B gene sequences, respectively. The phylogenies presented consistent, well supported, monophyletic groups in the parsimonious and likelihood analyses for both the nematode and bacterial strains and supported the placement of currently recognized taxa, from which a potentially new Heterorhabditis species represented by a Thailand strain MP68 was identified. While the nematode strains with distant geographic distributions showed no detectable phylogenetic divergence within H. bacteriophora or H. georgiana monophyletic groups, their respective symbiotic bacteria speciated into two Photorhabdus species: P. luminescens and P. temperata, indicating the occurrence of duplication. Although such evolutionary process reduces the phylogenetic congruence between Heterorhabditis nematodes and Photorhabdus bacteria, global cophylogenetic tests using ParaFit detected a highly significant correlation between the two phylogenies (ParaFitGlobal = 0.001). Further, the associations between H. zealandica, H. indica and H. megidis strains and their symbiotic bacteria exhibited significant contribution to the overall cophylogenetic structure. Overall, this study reveals evidence of coevolution between Photorhabdus bacteria and Heterorhabditis nematodes and provides a framework for further examination of the evolution of these associations.

Dissolved nutrients and atrazine removal by column-scale monophasic and biphasic rain garden model systems

Rain gardens are bioretention systems that have the potential to reduce peak runoff flow and improve water quality in a natural and aesthetically pleasing manner. We compared hydraulic performance and removal efficiencies of nutrients and atrazine in a monophasic rain garden design versus a biphasic design at a column-scale using simulated runoff. The biphasic rain garden was designed to increase retention time and removal efficiency of runoff pollutants by creating a sequence of water saturated to unsaturated conditions. We also evaluated the effect of C substrate availability on pollutant removal efficiency in the biphasic rain garden. Five simulated runoff events with various concentrations of runoff pollutants (i.e. nitrate, phosphate, and atrazine) were applied to the monophasic and biphasic rain gardens once every 5d. Hydraulic performance was consistent over the five simulated runoff events. Peak flow was reduced by approximately 56% for the monophasic design and 80% for the biphasic design. Both rain garden systems showed excellent removal efficiency of phosphate (89-100%) and atrazine (84-100%). However, significantly (p<0.001) higher removal of nitrate was observed in the biphasic (42-63%) compared to the monophasic rain garden (29-39%). Addition of C substrate in the form of glucose increased removal efficiency of nitrate significantly (p<0.001), achieving up to 87% removal at a treatment C/N ratio of 2.0. This study demonstrates the importance of retention time, environmental conditions (i.e. saturated/unsaturated conditions), and availability of C substrate for bioremediation of pollutants, especially nitrates, in rain gardens.

Transcriptional profiling of trait deterioration in the insect pathogenic nematode Heterorhabditis bacteriophora

Background

The success of a biological control agent depends on key traits, particularly reproductive potential, environmental tolerance, and ability to be cultured. These traits can deteriorate rapidly when the biological control agent is reared in culture. Trait deterioration under laboratory conditions has been widely documented in the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora (Hb) but the specific mechanisms behind these genetic processes remain unclear. This research investigates the molecular mechanisms of trait deterioration of two experimental lines of Hb, an inbred line (L5M) and its original parental line (OHB). We generated transcriptional profiles of two experimental lines of Hb, identified the differentially expressed genes (DEGs) and validated their differential expression in the deteriorated line.

Results

An expression profiling study was performed between experimental lines L5M and OHB of Hb with probes for 15,220 ESTs from the Hb transcriptome. Microarray analysis showed 1,185 DEGs comprising of 469 down- and 716 up-regulated genes in trait deteriorated nematodes. Analysis of the DEGs showed that trait deterioration involves massive changes of the transcripts encoding enzymes involved in metabolism, signal transduction, virulence and longevity. We observed a pattern of reduced expression of enzymes related to primary metabolic processes and induced secondary metabolism. Expression of sixteen DEGs in trait deteriorated nematodes was validated by quantitative reverse transcription-PCR (qRT-PCR) which revealed similar expression kinetics for all the genes tested as shown by microarray.

Conclusion

As the most closely related major entomopathogen to C. elegans, Hb provides an attractive near-term application for using a model organism to better understand interspecies interactions and to enhance our understanding of the mechanisms underlying trait deterioration in biological control agents. This information could also be used to improve the beneficial traits of biological control agents and better understand fundamental aspects of nematode parasitism and mutualism.

Comparative in vivo gene expression of the closely related bacteria Photorhabdus temperata and Xenorhabdus koppenhoeferi upon infection of the same insect host, Rhizotrogus majalis

BACKGROUND

Photorhabdus and Xenorhabdus are Gram-negative, phylogenetically related, enterobacteria, forming mutualism with the entomopathogenic nematodes Heterorhabditis and Steinernema, respectively. The mutualistic bacteria living in the intestines of the nematode infective juveniles are pathogenic to the insect upon release by the nematodes into the insect hemolymph. Such a switch needs activation of genes that promote bacterial virulence. We studied in vivo gene expression in Photorhabdus temperata and Xenorhabdus koppenhoeferi upon infection of the white grub Rhizotrogus majalis using selective capture of transcribed sequences technique.

RESULTS

A total of 40 genes in P. temperata and 39 in X. koppenhoeferi were found to be upregulated in R. majalis hemolymph at 24 h post infection. Genomic presence or upregulation of these genes specific in either one of the bacterium was confirmed by the assay of comparative hybridization, and the changes of randomly selected genes were further validated by quantitative real-time PCR. The identified genes could be broadly divided into seven functional groups including cell surface structure, regulation, virulence and secretion, stress response, intracellular metabolism, nutrient scavenging, and unknown. The two bacteria shared more genes in stress response category than any other functional group. More than 60% of the identified genes were uniquely induced in either bacterium suggesting vastly different molecular mechanisms of pathogenicity to the same insect host. In P. temperata lysR gene encoding transcriptional activator was induced, while genes yijC and rseA encoding transcriptional repressors were induced in X. koppenhoeferi. Lipopolysaccharide synthesis gene lpsE was induced in X. koppenhoeferi but not in P. temperata. Except tcaC and hemolysin related genes, other virulence genes were different between the two bacteria. Genes involved in TCA cycle were induced in P. temperata whereas those involved in glyoxylate pathway were induced in X. koppenhoeferi, suggesting differences in metabolism between the two bacteria in the same insect host. Upregulation of genes encoding different types of nutrient uptake systems further emphasized the differences in nutritional requirements of the two bacteria in the same insect host. Photorhabdus temperata displayed upregulation of genes encoding siderophore-dependent iron uptake system, but X. koppenhoeferi upregulated genes encoding siderophore-independent ion uptake system. Photorhabdus temperata induced genes for amino acid acquisition but X. koppenhoeferi upregulated malF gene, encoding a maltose uptake system. Further analyses identified possible mechanistic associations between the identified gene products in metabolic pathways, providing an interactive model of pathogenesis for each bacterium species.

CONCLUSION

This study identifies set of genes induced in P. temperata and X. koppenhoeferi upon infection of R. majalis, and highlights differences in molecular features used by these two closely related bacteria to promote their pathogenicity in the same insect host.

Transcriptomic analysis of the entomopathogenic nematode Heterorhabditis bacteriophora TTO1

BACKGROUND

The entomopathogenic nematode Heterorhabditis bacteriophora and its symbiotic bacterium, Photorhabdus luminescens, are important biological control agents of insect pests. This nematode-bacterium-insect association represents an emerging tripartite model for research on mutualistic and parasitic symbioses. Elucidation of mechanisms underlying these biological processes may serve as a foundation for improving the biological control potential of the nematode-bacterium complex. This large-scale expressed sequence tag (EST) analysis effort enables gene discovery and development of microsatellite markers. These ESTs will also aid in the annotation of the upcoming complete genome sequence of H. bacteriophora.

RESULTS

A total of 31,485 high quality ESTs were generated from cDNA libraries of the adult H. bacteriophora TTO1 strain. Cluster analysis revealed the presence of 3,051 contigs and 7,835 singletons, representing 10,886 distinct EST sequences. About 72% of the distinct EST sequences had significant matches (E value < 1e-5) to proteins in GenBank's non-redundant (nr) and Wormpep190 databases. We have identified 12 ESTs corresponding to 8 genes potentially involved in RNA interference, 22 ESTs corresponding to 14 genes potentially involved in dauer-related processes, and 51 ESTs corresponding to 27 genes potentially involved in defense and stress responses. Comparison to ESTs and proteins of free-living nematodes led to the identification of 554 parasitic nematode-specific ESTs in H. bacteriophora, among which are those encoding F-box-like/WD-repeat protein theromacin, Bax inhibitor-1-like protein, and PAZ domain containing protein. Gene Ontology terms were assigned to 6,685 of the 10,886 ESTs. A total of 168 microsatellite loci were identified with primers designable for 141 loci.

CONCLUSION

A total of 10,886 distinct EST sequences were identified from adult H. bacteriophora cDNA libraries. BLAST searches revealed ESTs potentially involved in parasitism, RNA interference, defense responses, stress responses, and dauer-related processes. The putative microsatellite markers identified in H. bacteriophora ESTs will enable genetic mapping and population genetic studies. These genomic resources provide the material base necessary for genome annotation, microarray development, and in-depth gene functional analysis.

Design and hydraulic characteristics of a field-scale bi-phasic bioretention rain garden system for storm water management

A field-scale bioretention rain garden system was constructed using a novel bi-phasic (i.e. sequence of anaerobic to aerobic) concept for improving retention and removal of storm water runoff pollutants. Hydraulic tests with bromide tracer and simulated runoff pollutants (nitrate-N, phosphate-P, Cu, Pb, and Zn) were performed in the system under a simulated continuous rainfall. The objectives of the tests were (1) to determine hydraulic characteristics of the system, and (2) to evaluate the movement of runoff pollutants through the system. For the 180 mm/24 h rainfall, the bi-phasic bioretention system effectively reduced both peak flow (approximately 70%) and runoff volume (approximately 42%). The breakthrough curves (BTCs) of bromide tracer suggest that the transport pattern of the system is similar to dispersed plug flow under this large runoff event. The BTCs of bromide showed mean 10% and 90% breakthrough times of 5.7 h and 12.5 h, respectively. Under the continuous rainfall, a significantly different transport pattern was found between each runoff pollutant. Nitrate-N was easily transported through the system with potential leaching risk from the initial soil medium, whereas phosphate-P and metals were significantly retained indicating sorption-mediated transport. These findings support the importance of hydraulics, in combination with the soil medium, when creating bioretention systems for bioremediation that are effective for various rainfall sizes and intervals.

Isolation and characterization of microsatellite loci in the entomopathogenic nematode Heterorhabditis bacteriophora

Twenty microsatellite loci were identified from genomic DNA enrichment and expressed sequence tags of entomopathogenic nematode Heterorhabditis bacteriophora. Eight loci were found to be polymorphic in a Northeast Ohio H. bacteriophora population. Levels of polymorphism were evaluated in 31-56 individuals and the number of alleles ranged from two to three. The values of observed and expected heterozygosities ranged from 0 to 0.536 and from 0.223 to 0.616, respectively. All eight loci showed heterozygote deficiencies, but three conformed to Hardy-Weinberg equilibrium at the subpopulation level. This is the first set of microsatellite markers in entomopathogenic nematodes.

Expressed sequence tag analysis of gene representation in insect parasitic nematode Heterorhabditis bacteriophora

We compared Heterorhabditis bacteriophora GPS11 expressed sequence tags (ESTs) to the ESTs of animal-parasitic, human-parasitic, plant-parasitic, and free-living nematodes. We identified 127 previously nondescribed ESTs of which 119 had homologs in ESTs and 8 had homologs in proteins of free-living nematodes. These ESTs were assigned putative functions in transcription, signal transduction, cell cycle control, metabolism, information processing, and cellular processes, thereby providing better insight into H. bacteriophora metabolism, sex determination, and signal transduction. We also identified 36 H. bacteriophora ESTs that had significant similarities to ESTs of parasitic nematodes, but not to ESTs or proteins of free-living nematodes species. Among these are the ESTs encoding a centrin, an ankyrin-repeat containing protein, and a nuclear hormone receptor. Our analysis also revealed that parasitic nematode-specific ESTs in this H. bacteriophora data set had more homologs in animal-parasitic nematodes than those parasitizing humans or plants.

Moraxella osloensis gene expression in the slug host Deroceras reticulatum

Background

The bacterium Moraxella osloensis is a mutualistic symbiont of the slug-parasitic nematode Phasmarhabditis hermaphrodita. In nature, P. hermaphrodita vectors M. osloensis into the shell cavity of the slug host Deroceras reticulatum in which the bacteria multiply and kill the slug. As M. osloensis is the main killing agent, genes expressed by M. osloensis in the slug are likely to play important roles in virulence. Studies on pathogenic interactions between bacteria and lower order hosts are few, but such studies have the potential to shed light on the evolution of bacterial virulence. Therefore, we investigated such an interaction by determining gene expression of M. osloensis in its slug host D. reticulatum by selectively capturing transcribed sequences.

Results

Thirteen M. osloensis genes were identified to be up-regulated post infection in D. reticulatum. Compared to the in vitro expressed genes in the stationary phase, we found that genes of ubiquinone synthetase (ubiS) and acyl-coA synthetase (acs) were up-regulated in both D. reticulatum and stationary phase in vitro cultures, but the remaining 11 genes were exclusively expressed in D. reticulatum and are hence infection specific. Mutational analysis on genes of protein-disulfide isomerase (dsbC) and ubiS showed that the virulence of both mutants to slugs was markedly reduced and could be complemented. Further, compared to the growth rate of wild-type M. osloensis, the dsbC and ubiS mutants showed normal and reduced growth rate in vitro, respectively.

Conclusion

We conclude that 11 out of the 13 up-regulated M. osloensis genes are infection specific. Distribution of these identified genes in various bacterial pathogens indicates that the virulence genes are conserved among different pathogen-host interactions. Mutagenesis, growth rate and virulence bioassays further confirmed that ubiS and dsbC genes play important roles in M. osloensis survival and virulence, respectively in D. reticulatum.

Identification of two down-regulated genes in entomopathogenic nematode Heterorhabditis bacteriophora infective juveniles upon contact with insect hemolymph

Entomopathogenic nematode Heterorhabditis bacteriophora infective juveniles (IJs) employ multiple strategies to combat with insect innate immune system after invasion. We employed suppressive subtractive hybridization (SSH) technique to study the gene expression in the IJs upon contact with the insect hemolymph in vitro. We identified two clones having higher expression levels in the IJs than IJs treated with insect hemolymph. The differential expression levels were confirmed by Northern blot hybridization with reference to the constitutive expression level of Heterorhabditis bacteriophora actin2 gene. Clone HbGPS11.C1G02 encoded a phosphofructokinase (PFK) with a 2.5 kb transcript and clone HbGPS11.C4C08 corresponded to a 2.1 kb transcript encoding a protein that had weak similarity to trans-sialidase from Trypanosoma cruzi. The differential expression of PFK in H. bacteriophora IJs before and during recovery process represented a switch from active movement in search of insect hosts to a state of combating insect innate immune system. This first report of H. bacteriophora differential gene expression provides a glimpse at the gene expression profile of H. bacteriophora IJ recovery process.

Biological control of terrestrial molluscs using Phasmarhabditis hermaphrodita--progress and prospects

Phasmarhabditis hermaphrodita Schneider (Nematoda: Rhabditidae) is a nematode that parasitises a wide range of slug and snail species. It has been formulated into a biological control agent (Nemaslug) and was commercialised in 1994. It is now available in fourteen European countries. A review is given of all research on P. hermaphrodita, including basic biology, mass cultivation, formulation, host range, application strategies, field efficacy and effects on non-target organisms. The many critical gaps in present knowledge are highlighted, and future research is proposed that will lead to greater understanding of this unusual parasite and may enable its more widespread use in the management of mollusc pests.

Differences in penetration routes and establishment rates of four entomopathogenic nematode species into four white grub species

We compared the penetration of the entomopathogenic nematodes Steinernema scarabaei (AMK001 strain), S. glaseri (NC1 strain), Heterorhabditis zealandica (X1 strain), and H. bacteriophora (GPS11 strain) into third-instars of the scarabs Popillia japonica, Anomala orientalis, Cyclocephala borealis, and Rhizotrogus majalis. When larvae were exposed to nematodes for 6-72 h larval mortality and nematode establishment rate and occasionally speed of kill often showed the same pattern within nematode-white grub combinations. But no two nematodes or white grub species had the same pattern for these observations for all white grub or nematode species, respectively. Mortality, establishment, and speed of kill followed a similar pattern for H. zealandica, S. glaseri, and S. scarabaei, but there was no clear relationship for H. bacteriophora. Significant nematode establishment was only observed after at least 48 h exposure in most nematode-white grub combinations. Faster establishment was observed only for H. zealandica in A. orientalis and R. majalis (after 24 h) and for S. scarabaei in P. japonica and R. majalis (after 12 h). Nematode establishment after 72 h in the different scarab species was generally low for S. glaseri (<1.5%) and H. bacteriophora (<3%), higher for H. zealandica (2-5%), and the highest for S. scarabaei (1-14%). However, in another experiment establishment was generally higher after 96h exposure. Nematode penetration sites were determined by comparing nematode establishment in larvae with mouth, anus, mouth+anus, or none sealed with glue. The trends for each nematode species were very similar in the different white grub species. H. zealandica and H. bacteriophora showed excellent cuticular penetration ability but may also penetrate through mouth and/or anus. S. glaseri also penetrated through the cuticle but lower establishment in larvae with mouth or mouth+anus sealed suggested that the mouth is an important penetration site. S. scarabaei showed a preference for the mouth as a penetration site, but it showed some cuticular penetration ability and may also use the anus as a penetration site. The methodology used cannot exclude that cuticular penetration also included penetration through the spiracles. To fully understand the effect of nematode and white grub species on nematode virulence, future studies will have to compare host immune response to the penetrating IJs and the role of the symbiotic bacteria in these interactions.

GENETIC VARIATION AND RELATIONSHIPS BETWEEN ISOLATES AND SPECIES OF THE ENTOMOPATHOGENIC NEMATODE GENUS HETERORHABDITIS DECIPHERED THROUGH ISOZYME PROFILES

We studied variation in isozyme patterns of 8 metabolic enzymes in 5 species of Heterorhabditis (H. bacteriophora, H. indica, H. marelata, H. megidis, and H. zealandica) comprising 18 isolates. Isozyme banding patterns of all the 8 enzymes were species specific; however, 3 enzymes, i.e., arginine kinase, fumarate hydratase, and malate dehydrogenase, displayed distinct patterns among all the 18 isolates. Phylogenetic analysis of the isozyme patterns produced dendrograms depicting a high degree of genetic variation among Heterorhabditis species, with the average pairwise distance of 0.2000. Trees constructed using different phylogenetic methods showed a relatively close genetic relationship between H. megidis and H. zealandica and between H. bacteriophora and H. indica. Also, H. bacteriophora HP88 was the most distant species from H. megidis (UK isolate), H. marelatus (Oregon isolate), and H. zealandica (X1 isolate) with pairwise distance of 0.1957, 0.2228, and 0.2120, respectively. Phylogenetic analysis also revealed genetic variation among H. bacteriophora isolates with the average pairwise distance of 0.1507. GPS2 and GPS3 were the most closely related isolates with the average distance of only 0.0870, followed by GPS1 and GPS2 with average distance of 0.1087. In contrast, KMD19 and HP88, OH25, and HP88, and OH25 and Acows isolates were the most divergent populations with a pairwise distance of 0.2011 and 37 character differences. Pairwise distance analysis also revealed that genetic divergence among populations of H. bacteriophora is relatively independent of geographic distance. Overall, these results demonstrate strong subspecies structuring in H. bacteriophora.

Infection Behavior and Overwintering Survival of Foliar Nematodes, Aphelenchoides fragariae, on Hosta

We studied the pathogenicity and overwintering survival of the foliar nematode, Aphelenchoides fragariae, infecting Hosta spp. Nematodes applied to either lower or upper sides of noninjured and injured hosta leaves were able to infect and produce typical symptoms on nine cultivars. Leaves of only four cultivars (Borschi, Fragrant Blue, Patomic Pride, and Olive Bailey Langdon) showed no symptoms of nematode infection. The nematodes overwintered as juveniles and adults in soil, dry leaves, and dormant buds, but not in roots. Nematode winter survival was higher in dormant buds and soil from the polyhouse than in an open home garden. Of the nematodes found in the dormant buds, 35% to 79% were located between the first two outside layers of the buds. The nematodes tolerated 8 hr exposure to 40 degrees C and -80 degrees C in leaf tissues. Relative humidity influenced nematode migration from soil to leaves. The presence of nematodes only on the outer surface of foliage (leaves and petioles) confirmed the migration of A. fragariae on the surface of the plants. Of the total number of nematodes found on the foliage, 25% to 46% and 66% to 77% were alive at 90% and 100% relative humidity, respectively, suggesting that high moisture is required for the survival and upward movement of nematodes. We conclude that A. fragariae can overwinter in soil, infected dry leaves, and dormant buds and migrate in films of water on the outer surface of the plant during spring to leaves to initiate infection.

Comparative analysis of the expressed genome of the infective juvenile entomopathogenic nematode, Heterorhabditis bacteriophora

We report the first cDNA-sequencing project of the entomopathogenic nematode, Heterorhabditis bacteriophora. A total of 1246 expressed sequence tags (ESTs) were generated by random sequencing of clones from a cDNA library of the infective juvenile stage. The ESTs were annotated resulting in 1072 useful ESTs that were categorized into functional categories according to Kyoto Encyclopedia of Genes and Genomes. Approximately 459 of 1072 ESTs (43%) had significant similarities to annotated sequences in GenBank. Of these, 417 had significant similarities to the free-living nematode Caenorhanditis elegans proteins. Most ESTs (18%) belonged to the genetic information processing category followed by metabolism (15% ESTs) and environmental information processing (15%) pathways. Several interesting ESTs were found that may have roles in the infectivity and survival of infective juveniles. These included proteases, dauer pathway genes (akt-1, pdk-1 & daf-7) and aging and stress resistance genes such as superoxide dismutase (sod-4), heat shock genes (hsp-4 & hsp-6), and eat genes, and signaling proteins like G-protein coupled receptors, regulators of G-protein signaling (rgs), and serine/threonine kinases. Other interesting ESTs include systemic RNAi defective protein (sid-1), ribonuclease III family members (rnh-2 &rnc) and transposase gene (Tc3A). About 67% of the ESTs did not find matches in any of the searched databases suggesting potentially novel genes in this enomopathogenic nematode. Note: Sequences described in this paper have been deposited in Genbank under the accessions DN 152655-DN 152999, and DN 153000-DN 153726.

Both heat-shock and cold-shock influence trehalose metabolism in an entomopathogenic nematode

Heat-shock response is highly conserved in animals and microorganisms, and it results in the synthesis of heat-shock proteins. In yeast, heat-shock response has also been reported to induce trehalose accumulation. We explored the relationship between heat- (35 C) or cold-shock (1 and 10 C) and trehalose metabolism in the entomopathogenic nematode, Heterorhabditis bacteriophora. Because both heat- and cold-shocks may precede desiccation stress in natural soil environments, we hypothesized that nematodes may accumulate a general desiccation protectant, trehalose, under both situations. Indeed, both heat- and cold-shocks influenced trehalose accumulation and activities of enzymes of trehalose metabolism in H. bacteriophora. Trehalose increased by 5- and 6-fold in heat- and cold-shocked infective juveniles, respectively, within 3 hr of exposure, compared with the nematodes maintained at 25 C (culture temperature). The activity of trehalose-6-phosphate synthase (T6PS), an enzyme involved in the synthesis of trehalose, also significantly increased in both heat- and cold-shocked nematodes during the first 3 hr of exposure. Generally, the trehalose levels and activities of T6PS declined to their original levels within 3 hr when nematodes were transferred back to 25 C. In both heat- and cold-shocked nematodes, trehalase activity decreased significantly within the first 3 hr and generally returned to the original levels within 3 hr when these nematodes were transferred back to 25 C. The results demonstrate that the trehalose concentrations in H. bacteriophora are influenced by both heat- and cold-shocks and are regulated by the action of 2 trehalose-metabolizing enzymes, T6PS and trehalase. The accumulated trehalose may enhance survival of nematodes under both cold and warm conditions, but it may also provide simultaneous protection against desiccation that may result from subsequent evaporation or freezing. This is the first report of the relationship between trehalose metabolism and heat-shock for the Nematoda.

RAPID AGE-RELATED CHANGES IN INFECTION BEHAVIOR OF ENTOMOPATHOGENIC NEMATODES

Nonfeeding infective juvenile (IJ) entomopathogenic nematodes (EPNs) are used as biological agents to control soil-dwelling insects, but poor storage stability remains an obstacle to their widespread acceptance by distributors and growers as well as a frustration to researchers. Age is one factor contributing to variability in EPN efficacy. We hypothesized that age effects on the infectiousness of IJs would be evident within the length of time necessary for IJs to infect a host. The penetration behavior of "young" (<1-wk-old) and "old" (2- to 4-wk-old) Heterorhabditis bacteriophora (GPS 11 strain), Steinernema carpocapsae (All strain), and Steinernema feltiae (UK strain) IJs was evaluated during 5 "exposure periods" to the larvae of the wax moth, Galleria mellonella. Individual larvae were exposed to nematode-infested soil for exposure periods of 4, 8, 16, 32, and 64 hr. Cadavers were dissected after 72 hr, and the IJs that penetrated the larvae were counted. Larval mortality did not differ significantly between 72- and 144-hr "observation periods," or points at which larval mortality was noted, for any age class or species. However, age and species effects were noted in G. mellonella mortality and nematode penetration during shorter time periods. Initial mortality caused by S. carpocapsae and H. bacteriophora IJs declined with nematode age but increased with S. feltiae IJ age. Young S. carpocapsae IJs penetrated G. mellonella larvae at higher rates than old members of the species (27-45% vs. 1-4%). Conversely, old S. feltiae IJs had higher penetration rates than young IJs (approximately 8 to 57% vs. 4 to approximately 31%), whereas H. bacteriophora IJs had very low penetration rates regardless of age (3-5.6%). Our results show that the effect of age on IJ infectiousness can be detected in IJs aged only 2 wk by a 4-hr exposure period to G. mellonella. These results have important implications for storage and application of EPNs and suggest the possibility of shortening the time required to detect nematodes in the soil.

Effectiveness of a Hot Water Drench for the Control of Foliar Nematodes Aphelenchoides fragariae in Floriculture

Effectiveness of a hot water drench for the control of Aphelenchoides fragariae infesting hosta (Hosta sp.) and ferns (Matteuccia pensylvanica) was studied. Drenching with hot water at 70 degrees C and 90 degrees C in October reduced (P < 0.05) A. fragariae in the soil but not in the leaves relative to the control (25 degrees C) 300 days after treatment (DAT). Plants drenched with 90 degrees C water had lower numbers of nematode-infected leaves per plant than those treated with 25 degrees C and 70 degrees C water (P < 0.05). Hot water treatments had no adverse effect on the growth parameters of hosta. Boiling water (100 degrees C) applied once a month for 3 consecutive months (April, May, June) consistently reduced the number of infected leaves and the severity of infection relative to the control 150 DAT in hosta but not in ferns (P < 0.05). Boiling water (100 degrees C) caused a 67% reduction in A. fragariae population in hosta leaves, 50% in fern fronds, and 61% to 98% in the soil over the control 150 DAT. A boiling water drench had no effect on the fern growth but caused 49% and 22% reduction in the number and size of hosta leaves, respectively, over the control in 2002. We conclude that 90 degrees C water soil drench in the autumn or early spring could prove effective in managing foliar nematodes on hosta in nurseries and landscapes.

Evaluation of a contraction flow field on hydrodynamic damage to entomopathogenic nematodes?A biological pest control agent

Mechanized production and delivery of biological pesticides presents challenges because the biological agents must remain viable during these processes. This study evaluates the effect of flow through an abrupt contraction, where flow characteristics similar to that found within bioprocesses and spray equipment are developed, on damage to a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). An opposed-pistons, contraction flow device generated volumetric flow rates ranging between 8.26 cm(3)/s and 41.3 cm(3)/s. Four EPN species were evaluated: Heterorhabditis bacteriophora, Heterorhabditis megidis, Steinernema carpocapsae, and Steinernema glaseri. Damage was quantified by counting living and dead EPNs. Optical and cold field emission scanning electron microscope (CFE-SEM) images provided qualitative information to describe how the damage occurred. The experimental flow field was completely described using FLUENT, a computational fluid dynamics program. Local flow parameters computed in FLUENT were compared to EPN damage. The type and extent of damage varied between EPN species. Damaged Heterorhabditis spp. generally remained whole with an internal rupture located near the center of the body, while Steinernema spp. most often broke into several pieces. The fast-transient stress field generated at the entrance to the contraction caused a momentary tensile loading and then relaxation that damaged the EPNs. At high flow rates, the tensile stresses became large enough to cause failure of the EPN structural membrane. The relative elasticity of the EPN structural membrane may explain the differences in damage observed between the species. It is speculated that the internal rupture of the Heterorhabditis spp. occurred during the processes of stretching and relaxing at the contraction entrance. Appreciable damage was observed at lower average energy dissipation rates for H. bacteriophora (1.23E + 8 W/m(3)), H. megidis (1.72E + 8 W/m(3)), and S. glaseri (2.89E + 8 W/m(3)) compared to S. carpocapsae (3.70E + 8 W/m(3)). Energy dissipation rates within an equipment component should be kept below 1E + 8 W/m(3) to avoid hydrodynamic damage to EPNs. The relationship between average energy dissipation and EPN damage provides important information for future simulation efforts of actual spray equipment components.

Parasitism of molluscs by nematodes: types of associations and evolutionary trends

Although there are no confirmed fossil records of mollusc parasitic nematodes, diverse associations of more than 108 described nematode species with slugs and snails provide a fertile ground for speculation of how mollusc parasitism evolved in nematodes. Current phylogenic resolution suggests that molluscs have been independently acquired as hosts on a number of occasions. However, molluscs are significant as hosts for only two major groups of nematodes: as intermediate hosts for metastrongyloids and as definitive hosts for a number of rhabditids. Of the 61 species of nematodes known to use molluscs as intermediate hosts, 49 belong to Metastrongyloidea (Order Strongylida); of the 47 species of nematodes that use molluscs as definitive hosts, 33 belong to the Order Rhabditida. Recent phylogenetic hypotheses have been unable to resolve whether metastrongyloids are sister taxa to those rhabditids that use molluscs as definitive hosts. Although most rhabditid nematodes have been reported not to kill their mollusc hosts prior to their reproduction, some species are pathogenic. In fact, infective juveniles of Phasmarhabditis hermaphrodita vector a lethal bacterium into the slug host in which they reproduce. This life cycle is remarkably similar to the entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae. Also, the discoveries of Alloionema and Pellioditis in slugs are interesting, as these species have been speculated to represent the ancestral forms of the entomopathogenic nematodes. Development of the infective stage appears to be an important step toward the acquisition of molluscs as definitive hosts, and the association with specific bacteria may have arisen in conjunction with the evolution of necromeny.

Does mowing height influence alkaloid production in endophytic tall fescue and perennial ryegrass?

The mutualistic symbiosis following infection of tall fescue, Festuca arundinacea, and perennial ryegrass, Lolium perenne, by fungal endophyte (Neotyphodium spp.) results in the production of alkaloids that are feeding deterrents or toxic to insects and livestock. If the levels of the alkaloids can be manipulated by cultural practices in the grasses that are used for home lawns and golf courses, this could alleviate the need for pesticide applications in urban environments. We evaluated the influence of mowing height on the levels of some alkaloids in a greenhouse experiment for two consecutive months. In tall fescue, levels of four of the nine alkaloids, including one presumptive alkaloid, showed increased levels with increasing the mowing height from 2.5 to 7.5 cm. The alkaloids were ergonovine, ergocryptine, perloline methyl ether, and an unidentified alkaloid designated as unknown C. In perennial ryegrass, three out of six alkaloids, perloline methyl ether, chanoclavine, and unknown A, showed similar increases. The alkaloid levels in perennial ryegrass showed more variability than those in tall fescue between the two sampling dates. It was clear in both grasses that the relative levels of the alkaloids varied with mowing height, as well as over time.

Effect of osmotic desiccation on longevity and temperature tolerance of Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae)

Limited storage stability severely restricts the biological control potential of slug-parasitic nematodes. In a series of experiments, we evaluated the effects of temperature and osmotic desiccation on the short- and long-term survival of the slug-parasitic nematode Phasmarhabditis hermaphrodita. Nematode survival in petri dishes at 1,500 infective juveniles/ml did not differ significantly at 5, 10, and 15 C but declined rapidly at 25 and 30 C. At 25 C about 50% of the nematodes survived for 4 wk, but at 30 C no nematode survived past 1 day. About 50% of the nematodes survived for 32 wk at 20 C. About 35-40% of the nematodes survived up to a year at 5, 10, and 15 C. Phasmarhabditis hermaphrodita showed poor survival under osmotic desiccation in glycerol with 15 and 20% glycerol significantly reducing survival at 5 and 15 C. Although the nematodes tolerated 10% glycerol, this level of desiccation also did not enhance long-term survival at either 5 or 15 C. There was a significant decrease in nematode survival in 10% glycerol at 25 C during the first 2-3 wk, but about 16% of the nematodes survived for 6 wk in 10% glycerol as compared with only 1% survival in water. The greatest benefit of osmotic desiccation in glycerol was observed in the enhanced survival of P. hermaphrodita at temperature extremes. Over 96% of the nematodes survived a 6-hr exposure to 35 C in 10% glycerol, whereas only 9% survived in water. Similarly, over 90% of the nematodes survived an exposure to -20 C for 4 hr in 10% glycerol, but less then 2% survived in water. We conclude that 5-15 C is an optimum temperature range for the storage of P. hermaphrodita. We also conclude that osmotic desiccation in 10% glycerol can substantially increase survival of P. hermaphrodita at temperature extremes (35 and -20 C) for short periods but has no effect on nematode longevity at the optimum temperature range of 5-15 C.

Characterization of the first molluscicidal lipopolysaccharide from Moraxella osloensis

Moraxella osloensis is a bacterium that is mutualistically associated with Phasmarhabditis hermaphrodita, a nematode that has potential for the biocontrol of mollusk pests, especially the slug Deroceras reticulatum. We discovered that purified M. osloensis lipopolysaccharide (LPS) possesses a lethal toxicity to D. reticulatum when administered by injection but no contact or oral toxicity to this slug. The toxicity of the LPS resides in the lipid A moiety. M. osloensis LPS was semiquantitated at 6 x 10(7) endotoxin units per mg. The LPS is a rough-type LPS with an estimated molecular weight of 5,300. Coinjection of galactosamine with the LPS increased the LPS's toxicity to the slug two- to four-fold. The galactosamine-induced sensitization of the slug to the LPS was reversed completely by uridine.

Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.