Endoparasitic Fungi Research Articles

A review on unravelling the medicinal properties of magical mushrooms: Cordyceps militaris

Nowadays, the public and the scientific communities are choosing and looking for natural remedies as an alternative to the elaborate chemically synthesised drugs. As a result, due to its immunostimulatory potential, Cordyceps genus has grabbed attention from the scientific community in recent years. Various in vivo and in vitro investigations on the endo-parasitic fungi have shown its tremendous pharmaceutical potential owing to the various bioactive constituents. Pre-clinical studies have revealed its activities like anti-cancer, anti-diabetic, antioxidant, vasorelaxation, antihyperlipidemic, anticholesterolemic, hypotensive, anti-aging, anti-fatigue, kidney protection and aphrodisiac. Moreover, Cordyceps species are also related with stimulation of the immune system- stimulating inflammatory response mediated via mitogen activated protein (MAP) kinase pathway, stimulation of phagocytosis, and cytokine production such as interleukins (IL)-10, IL-12, and tumour necrosis factor alpha (TNF) etc. In the present review, we discuss the various bioactive compounds of the fungi such as nucleosides, alkaloids, flavonoids and their therapeutic potential. We also highlight its culturing methods and its current status in the global market.

The Potential of Esteya spp. for the Biocontrol of the Pinewood Nematode, Bursaphelenchus xylophilus.

The pinewood nematode (PWN), Bursaphelenchus xylophilus, is the causal agent of pine wilt disease (PWD) and a quarantine organism in many countries. Managing PWD involves strict regulations and heavy contingency plans, and present climate change scenarios predict a spread of the disease. The urgent need for sustainable management strategies has led to an increasing interest in promising biocontrol agents capable of suppressing the PWN, like endoparasitic nematophagous fungi of the Esteya genus. Here, we review different aspects of the biology and ecology of these nematophagous fungi and provide future prospects.

Pathogenicity and Metabolites of Endoparasitic Nematophagous Fungus Drechmeria coniospora YMF1.01759 against Nematodes.

Plant parasitic nematodes cause severe damage to crops. Endoparasitic nematophagous fungi (ENF) are a type of important biocontrol fungi, which can cause disease or kill nematodes by producing various spores. As a major ENF, Drechmeria coniospora displays certain potential for controlling plant-parasitic nematodes. In this study, the pathogenicity and secondary metabolites of the endoparasitic fungus D. coniospora YMF1.01759 were investigated. The strain D. coniospora YMF1.01759 had high infection efficiency against nematodes. The process of infecting nematodes by the strain was observed under an electron microscope. Here, 13 metabolites including one new compound 4(S)-butoxy-3-(butoxymethyl)-2-hydroxycyclopent-2-en-1-one (2) were isolated and identified from the fermentation products of D. coniospora YMF1.01759 cultured in a SDAY solid medium. Furthermore, a bioassay showed that 5-hydroxymethylfuran-2-carboxylic acid (1) is toxic to the root knot nematode Meloidogyne incognita and affects the hatching of its egg. Thereby, the nematicidal mortality attained 81.50% at 100 μg/mL for 48 h. Furthermore, egg hatching was inhibited at the tested concentrations, compared with water control eggs. This is the first report on the secondary metabolites of the ENF D. coniospora. The results indicated that D. coniospora could infect nematodes by spores and produce active metabolites to kill nematodes. The biological control potential of D. coniospora against nematodes was expounded further.

Impact of vineyard ground cover management on the occurrence and activity of entomopathogenic nematodes and associated soil organisms

Viticulture is a valuable sector worldwide with an extraordinary socio-economic impact in Spain. Numerous pests and diseases threaten vineyards, and their management primarily relies on the use of conventional agrochemicals. The current paradigm of sustainability pursues the implementation of ecologically sound strategies in vineyard ecosystems. The use of cover crops is arising as an alternative with numerous benefits, including favoring above-belowground biodiversity and the presence of beneficial soil organisms such as the entomopathogenic nematodes (EPNs). We hypothesized that the use of specific cover crops in vineyards might enhance the natural occurrence and activity of EPNs by modulating the assemblage with associated organisms. We performed the experiments in an ongoing experimental vineyard (Vitis vinifera var Tempranillo, clon RJ-26, rootstock ‘110-Richter’) located in Logroño (Spain), drove with different soil management systems (three replicates each): conventional tillage practice and the cover crops (i) seeded with Bromus catharticus (Poaceae), (ii) flower-driven, and (iii) spontaneous. We took four soil composite samples per plot (n = 48 per sampling time) late spring and early autumn in two consecutive years (2017 and 2018). By using species-specific primers/probes qPCR sets, we screened for the presence and abundance of eight EPNs species and 12 related soil organisms: six nematophagous fungi, four free-living nematodes, and two ectoparasitic bacteria. Additionally, we assessed the EPN activity by the traditional insect-bait method. Overall, we recorded higher EPN numbers or activity rates on cover crops than on bare soils. However, some of the results were divergent among no-till treatments. We observed not only higher EPN abundance and activity on spontaneous covers but lower numbers of antagonistic organisms, particularly endoparasitic nematophagous fungi. Thus, according to our results, the use of spontaneous covers could be the most promising strategy to support the conservation biological control service provided by the naturally occurring EPN species in vineyards, plus with a low cost for the sector.

The Diversity and Distribution of Wolbachia, Rhizobiales, and Ophiocordyceps Within the Widespread Neotropical Turtle Ant, Cephalotes atratus (Hymenoptera: Formicidae).

Ants are an ecologically and evolutionarily diverse group, and they harbor a wide range of symbiotic microbial communities that often greatly affect their biology. Turtle ants (genus Cephalotes) engage in mutualistic relationships with gut bacteria and are exploited by microbial parasites. Studies have shown that associations among these microbial lineages and the turtle ant hosts vary geographically. However, these studies have been limited, and thorough within-species analyses of the variation and structure of these microbial communities have yet to be conducted. The giant turtle ant, Cephalotes atratus (Linnaeus 1758), is a geographically widespread, genetically diverse Neotropical species that has been sampled extensively across its geographic range, making it ideal for analysis of microbial associations. In this study, we verified the presence, genetic variation, and geographic patterns at the individual, colony, and population level of three microbial groups associated with the giant turtle ant: Wolbachia, a genus of facultative bacteria which are often parasitic, affecting host reproduction; Rhizobiales, a mutualistic order of bacteria hypothesized to be an obligate nutritional symbiont in turtle ants; and Ophiocordyceps, a genus of endoparasitic fungi infecting many arthropod species by manipulating their behavior for fungal reproduction. In this study, we found varying degrees of prevalence for two distantly related genotypes (haplogroups) of Wolbachia and high degree of prevalence of Rhizobiales across colonies with little genetic variation. In addition, we found low occurrence of Ophiocordyceps. This study highlights a key first step in understanding the diversity, distribution, and prevalence of the microbial community of C. atratus.

Research advances on resource and biological control of endoparasitic fungi.

Endoparasitic fungi are a group of nematophagous fungi which produce a variety of special spores to infect free nematodes. They play a key role in maintaining the population density of nematodes in the natural systems. Moreover, they are important materials for the study of species diversity. Therefore, they have special research significance and economic values. At present, many studies mainly focus on the infectivity of trapping fungi to nematodes, and mainly directed at the second instars larvae. However, the endoparasitic fungi have infectivity to nematodes at all stages. Here, we reviewed the resource status, diversity of spore morphology, infection modes, life history and host of endoparasitic fungi, and the biocontrol fungi with development potential and their commercialized application. Finally, we proposed some suggestions for future researches.

Signal pathways involved in microbe-nematode interactions provide new insights into the biocontrol of plant-parasitic nematodes.

Plant-parasitic nematodes (PPNs) cause severe damage to agricultural crops worldwide. As most chemical nematicides have negative environmental side effects, there is a pressing need for developing efficient biocontrol methods. Nematophagous microbes, the natural enemies of nematodes, are potential biocontrol agents against PPNs. These natural enemies include both bacteria and fungi and they use diverse methods to infect and kill nematodes. For instance, nematode-trapping fungi can sense host signals and produce special trapping devices to capture nematodes, whereas endo-parasitic fungi can kill nematodes by spore adhesion and invasive growth to break the nematode cuticle. By contrast, nematophagous bacteria can secrete virulence factors to kill nematodes. In addition, some bacteria can mobilize nematode-trapping fungi to kill nematodes. In response, nematodes can also sense and defend against the microbial pathogens using strategies such as producing anti-microbial peptides regulated by the innate immunity system. Recent progresses in our understanding of the signal pathways involved in microbe-nematode interactions are providing new insights in developing efficient biological control strategies against PPNs. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.

Amoebophagous Fungi as Predators and Parasites of Potentially Pathogenic Free-living Amoebae

There are numerous case reports indicating that naked Free-Living Amoebae (FLA) can relatively easily get to humans or animals. The presence of pathogenic amoebae in habitats related to human activities supports the public health relevance of FLA. Acanthamoebae, Naegleria fowleri, Balamuthia mandrillaris and several other FLA have proved to be facultative human pathogenic microorganisms. Additionally, a wide range of FLA is known as vectors of pathogenic microorganisms (endocytobionts). Within their biocoenosis, FLA and fungi (and other microorganisms) live sympatrically. It is known that fungi serve as food sources for the phagocytotic active (mycophagous) trophozoite stages of FLA. In contrast, amoebophagous fungi may use FLA as prey organisms. Endoparasitic and predaceous fungi prove that there are numerous different interactions between FLA and fungi. The man-made introduction of suitable fungi into a habitat (soil or water) with human pathogenic FLA may overcome any ecological effects or limits. While nematophagous fungi have already been brought into action against harmful nematodes, the usage of amoebophagous fungi against FLA has not been widely considered. Nevertheless, the results from in vitro studies are promising concerning the targeted use of amoebophagous fungi as biological control measures against FLA in limited natural areas, in soil and in aquatic habitats.

Comparative genomic analyses reveal the features for adaptation to nematodes in fungi.

Nematophagous (NP) fungi are ecologically important components of the soil microbiome in natural ecosystems. Esteya vermicola (Ev) has been reported as a NP fungus with a poorly understood evolutionary history and mechanism of adaptation to parasitism. Furthermore, NP fungal genomic basis of lifestyle was still unclear. We sequenced and annotated the Ev genome (34.2 Mbp) and integrated genetic makeup and evolution of pathogenic genes to investigate NP fungi. The results revealed that NP fungi had some abundant pathogenic genes corresponding to their niche. A number of gene families involved in pathogenicity were expanded, and some pathogenic orthologous genes underwent positive selection. NP fungi with diverse morphological features exhibit similarities of evolutionary convergence in attacking nematodes, but their genetic makeup and microscopic mechanism are different. Endoparasitic NP fungi showed similarity in large number of transporters and secondary metabolite coding genes. Noteworthy, expanded families of transporters and endo-beta-glucanase implied great genetic potential of Ev in quickly perturbing nematode metabolism and parasitic behavior. These results facilitate our understanding of NP fungal genomic features for adaptation to nematodes and lay a solid theoretical foundation for further research and application.

Synergetic suppression of soybean cyst nematodes by chitosan and Hirsutella minnesotensis via the assembly of the soybean rhizosphere microbial communities

Chitosan, a deacetylated form of chitin, has been shown to enhance the biocontrol efficacy of nematophagous fungi to parasitize nematodes. However, the mechanism by which nematode endoparasitic fungi with chitosan suppresses disease caused by the soybean cyst nematode (SCN; Heterodera glycines) through the rhizosphere microbiota remains unclear. In this study, we performed a greenhouse experiment with soybean grown in five soil treatments. Strong synergetic suppression of the SCN egg density was observed using a combined treatment of H. minnesotensis and chitosan (SHg+Hm+Ch), followed by treatments with H. minnesotensis (SHg+Hm) or chitosan (SHg+Ch). The parasitism of SCN juveniles (J2) and amount of H. minnesotensis DNA were significantly increased by the presence of chitosan in soil. The bacterial and fungal communities of the soybean rhizosphere, profiled by the Illumina high-throughput pyrosequencing, showed that the rhizobacterial OTU richness was decreased by SHg (nematode infested), SHg+Hm, SHg+Ch, and SHg+Hm+Ch treatments, and fungal richness was increased by the same treatments except for SHg+Ch, compared to the mock-inoculated plants (S). Overall, the bacterial and fungal community structures were different among the different treatments, and soil containing chitosan was distinct from H. minnesotensis with and without chitosan as well as from nematode infested or uninfested soils. Except for the enhancement of H. minnesotensis, chitosan also increased the bacterial genus Streptomyces and fungal genera Purpureocillium and Pochonia, which have been documented to suppress SCN in the soybean rhizosphere. Combined application of H. minnesotensis and chitosan led to shifts in the abundance of the core rhizobacterial and rhizofungal taxa that respond to soil suppression of SCN. In this study, we provide evidence that chitosan shifts the abundance of resident and inoculated biocontrol agents in the rhizosphere to suppress pathogens.

Decay of the glycolytic pathway and adaptation to intranuclear parasitism within Enterocytozoonidae microsporidia.

Glycolysis and oxidative phosphorylation are the fundamental pathways of ATP generation in eukaryotes. Yet in microsporidia, endoparasitic fungi living at the limits of cellular streamlining, oxidative phosphorylation has been lost: energy is obtained directly from the host or, during the dispersive spore stage, via glycolysis. It was therefore surprising when the first sequenced genome from the Enterocytozoonidae - a major family of human and animal-infecting microsporidians - appeared to have lost genes for glycolysis. Here, we sequence and analyse genomes from additional members of this family, shedding new light on their unusual biology. Our survey includes the genome of Enterocytozoon hepatopenaei, a major aquacultural parasite currently causing substantial economic losses in shrimp farming, and Enterospora canceri, a pathogen that lives exclusively inside epithelial cell nuclei of its crab host. Our analysis of gene content across the clade suggests that Ent. canceri's adaptation to intranuclear life is underpinned by the expansion of transporter families. We demonstrate that this entire lineage of pathogens has lost glycolysis and, uniquely amongst eukaryotes, lacks any obvious intrinsic means of generating energy. Our study provides an important resource for the investigation of host-pathogen interactions and reductive evolution in one of the most medically and economically important microsporidian lineages.

The transcription factor SKN7 regulates conidiation, thermotolerance, apoptotic-like cell death and parasitism in the nematode endoparasitic fungus Hirsutella minnesotensis.

The transcription factor SKN7 is a highly conserved protein among fungi and was initially recognized as a response regulator that protects cells from oxidative stress and maintains cell wall integrity in yeast. Orthologs of SKN7 are extensively present in biocontrol agents of plant pathogens, but they had not been functionally characterized. Here, we identified and characterized the transcription factor SKN7 in the nematode endoparasitic fungus Hirsutella minnesotensis. Null mutant lacking HIM-SKN7 (HIM_03620), which was generated by a gene disruption strategy, demonstrated reduced conidiation, increased sensitivity to high temperature, hydrogen peroxide, mannitol and ethanol, and reduced fungal resistance to farnesol. However, over-expression mutant showed increased conidial production, thermotolerance and resistance to farnesol, suggesting that HIM-SKN7 regulates antiapoptotic-like cell death in H. minnesotensis. Moreover, the results showed that in null mutant, H. minnesotensis had decreased endoparasitic ability as compared to wild type and over-expression strain. During the infection process, the relative expression of the HIM-SKN7 gene was significantly induced in the wild type and over-expression strain. The results of the present study advance our understanding of the functions of the SKN7 gene in biocontrol agents, in particular, nematode endoparasitic fungi.

Entomopathogenic nematode food web assemblages in Florida natural areas

In Florida citrus orchards, root weevil herbivory is tempered by four native entomopathogenic nematode (EPN) species whose spatial patterns are associated with soil properties related to water content. Manipulation of these variables could affect the efficacy and conservation of native EPNs for control of root weevils. The diversity of EPNs in non-agricultural areas it is unknown. We speculated that, whereas different species composition may occur in some natural areas by virtue of non-citrus niche adaptations, similar soil properties and environmental conditions should shape the communities in both systems. We characterized EPN food web assemblages during summer-fall 2011 in 91 sites comprising five naturally occurring botanical groups (oak, pine, palm and palmetto, mixed and other) and two ecoregions (central ridge and flatwoods). We used species-specific qPCR probes for 13 EPN species, two species of Paenibacillus (ectoparasitically associated with EPNs), seven species of nematophagous fungi (NF), an oomycete pathogen of citrus (Phytophthora nicotianae) and free-living bactivorous nematodes (Acrobeloides-group), some of which compete with EPNs. Seven EPN species were detected at frequencies about 60% of that reported from citrus. Additional species detected were Steinernema glaseri and Heterorhabditis floridensis, whereas citrus inhabitants Steinernema riobrave and Steinernema scapterisci, were absent, suggesting a possible niche adaptation. EPN recovery frequency did not differ between two ecoregions, except for Heterorhabditis indica which was detected at more sites in the flatwoods than on the central ridge and Heterorhabditis zealandica exhibiting the opposite pattern for detection frequency and abundance. Nor did the botanical habitats much affect EPNs other than H. indica which occurred with greatest frequency and abundance in abandoned citrus orchards. Soil moisture appeared to be important in modulating these subterranean communities, with groundwater depth, organic matter, soil clay and pH explaining significant EPN variability between sites. There was little evidence that regional or habitat differences in natural enemy occurrence affected the EPN spatial patterns. Indeed, numerous significant direct associations between species of nematodes and nematophagous fungi suggested that the local abundance of the r-selected EPN and Acrobeloides-group nematodes is an important resource modulating population growth of these trapping and endoparasitic fungi. Congruent relationships between EPN spatial patterns and soil properties that affect water potential in both natural areas and citrus orchards suggests that soil moisture drives these patterns and modulates the regulation of root herbivores by EPNs in this part of the Florida peninsula. Consequently, management of soil moisture by manipulating these properties has the greatest potential to enhance and conserve EPN services.

Screening of different sample types associated with sheep and cattle for the presence of nematophagous fungi in China.

A total of 1502 samples, including feces of sheep (793) and cattle (348), pasture soil (118), dung compost (147) and barn soil (96), were examined between October 2012 and August 2014 to discover potential strains of nematophagous fungi for the biological control of livestock-parasitic nematodes. These samples were collected from 87 sites located in 48 counties of 20 provinces (autonomous regions/municipalities) of China. Fungi were identified down to a species level. Four hundred and seventy-seven isolates, which were distributed in 8 genera and 28 taxa, were identified as nematophagous fungi. Nematode-trapping fungi included 17 species and one unidentified species of Arthrobotrys, two of Dactylella, Drechslerella dactyloides, and Duddingtonia flagrans. Five identified species and two unidentified species of endoparasitic fungi were isolated. The predominant species from all regions were Arthrobotrys oligospora, followed by Arthrobotrys musiformis, Arthrobotrys (Monacrosporium) thaumasiun, and Arthrobotrys (Monacrosporium) microscaphoides. Species with adhesive networks were the most frequently isolated. Among the endoparasitic fungi, Podocrella harposporifera (Harposporium anguillulae) was the most common species, followed by Harposporium lilliputanum and Harposporium arcuatum. Based on Shannon diversity index, the diversity levels of nematophagous fungi were relatively higher in samples associated with cattle, barn soil, and subtropical monsoon climate zone. Three species isolated from this study, namely, Duddingtonia flagrans, Arthrobotrys salina (Monacrosporium salinum), and Arthrobotrys oligospora var. sarmatica, are newly recorded in China, and 20 species (including one unidentified species) are newly recorded in sheep and cattle barn soils worldwide.

Development of a transformation system for Hirsutella spp. and visualization of the mode of nematode infection by GFP-labeled H. minnesotensis.

Hirsutella rhossiliensis and H. minnesotensis are endoparasitic fungi of the second-stage juvenile (J2) of the soybean cyst nematode (Heterodera glycines) in nature. They also parasitize both H. glycines J2 and Caenorhabditis elegans on agar plates. Agrobacterium tumefaciens-mediated transformation conditions were established for these Hirsutella spp. The resulting transformants were similar to the corresponding wild-type strains. The infection processes of H. glycines J2 and C. elegans second larval stage (L2) by H. minnesotensis expressing ZsGreen were microscopically analyzed. Conidia of H. minnesotensis adhered to passing nematodes within 8 h post-inoculation (hpi), formed an infection peg between 8 and 12 hpi, and penetrated the nematode cuticle between 12 and 24 hpi for C. elegans L2 and between 12 and 32 hpi for H. glycines J2. Hyphal proliferation inside of the nematode coelom was observed at approximately 32 hpi for C. elegans L2 and at approximately 40 hpi for H. glycines J2. The fungus consumed the whole body and grew out to produce conidia at approximately 156 and 204 hpi for C. elegans L2 and H. glycines J2, respectively. The efficient transformation protocol and a better understanding of infection process provide a solid foundation for studying the molecular and cellular mechanisms underlying fungal parasitism of nematodes.

Nematophagous fungi from decomposing cattle faeces in Argentina

BackgroundBiological control of gastrointestinal nematodes of ruminants by use of nematophagous fungi would become part of any livestock parasite integral control system. Identifying autochthonous species that could then be selected for mass production is an important phase in the practical use of biological control. AimsTo search for nematophagous fungi with potential use as biological control agents against gastrointestinal nematodes in Argentina. MethodsDecomposing cattle faeces sampled in different locations were incubated in water agar 2% with Panagrellus sp. The developed nematophagous fungi were transferred to new water agar 2% plates and then to corn meal agar plates in order to carry out their identification. Fungal diversity and richness were also assessed. ResultsSeventeen species from nine genera of nematophagous fungi were found. Twelve species were nematode-trapping fungi and three species plus two fungi identified to genus level corresponded to endoparasitic fungi. Arthrobotrys conoides, Arthrobotrys oligospora, Duddingtonia flagrans, Monacrosporium doedycoides, Arthrobotrys robusta and Drechmeria coniospora were the most frequently isolated species overall in the whole study (6.6%, 5.7%, 5.7%, 5.7%, 4.7% and 4.7%, respectively) although other species were more frequently recorded at local levels such as Arthrobotrys pyriformis (18.8%). Only A. conoides has been previously isolated from ruminant faecal samples in Argentina. Five nematode-trapping fungal species are mentioned for the first time in the Americas ConclusionsD. flagrans and A. conoides, both identified in the present study, are among the most promising ones as biological control agents against gastrointestinal nematodes of ruminants.

Article for the “Free-living amoebae Special Issue”: Isolation and characterisation of various amoebophagous fungi and evaluation of their prey spectrum

This article gives an overview on the isolation and characterisation of endoparasitic fungi invading free-living amoebae (FLA), including the ones forming thalli inside their hosts such as Cochlonema euryblastum and also the predatory fungi which capture amoebae by adhesive hyphae. Acaulopage spp. and Stylopage spp. trap, intrude, and exploit amoebal trophozoites. Previous phylogenetic studies proved Cochlonema to be a member of the Zoopagales. The genetic investigation of Acaulopage tetraceros demonstrated its close relationship to Cochlonema. Co-cultivation of A. tetraceros with a number of FLA revealed a great prey spectrum of this amoebophageous fungus. In addition it was shown that solitary amoebal stages of slime moulds such as Dictyostelium sp. and Physarum sp. are also suited as welcome prey amoebae.

Ecto- and Endoparasitic Fungi on Ants from the Holarctic Region

The ant-specific fungiAegeritella, Laboulbenia, Rickia, Hormiscium,andMyrmicinosporidiumin the Holarctic region—nine species—are reviewed. Present knowledge is highly biased geographically, as shows the single record for Holarctic Asia, and this is to solve. The phylogenetic position ofAegeritella, Hormiscium, andMyrmicinosporidiumis unknown. Hosts seem to be also skewed phylogenetically although this may be a true pattern.

Purification, characterization, and gene cloning of an alkaline serine protease from a highly virulent strain of the nematode-endoparasitic fungus Hirsutella rhossiliensis

Hirsutella rhossiliensis OWVT-1 has substantial potential as a biocontrol agent against plant-parasitic nematodes. Serine proteases have emerged as a potentially useful factor in the nematode-fungus interactions. When grown in liquid culture with the nematode Panagrellus redivivus as the sole nitrogen source, an extracellular alkaline protease (Hasp) was produced by the OWVT-1. The purified Hasp killed the juveniles of the soybean-cyst nematode (Heterodera glycines) and degraded proteins of the nematode cuticle. The molecular mass of Hasp was estimated to be 33 kDa. The optimum pH and temperature for enzyme activity were pH 9 and 75 degrees C. The amino acid sequence obtained by the N-terminal sequence analysis was applied for the primer design to isolate the Hasp cDNA gene, which consists of 1170 bp open reading frame. Analysis of the cDNA and corresponding genomic sequence revealed that Hasp included four exons (279, 186, 513, and 192 bp) divided by three introns (65, 99, and 93 bp). Southern blotting showed that Hasp was a single-copy gene in the genome. The deduced amino acid sequence was very similar to other serine proteases of endoparasitic and egg-parasitic fungi of nematodes and of entomopathogenic fungi but was less similar to the serine proteases of nematode-trapping fungi. In a phylogenetic analysis of the amino acid sequences of serine proteases, the serine protease of H. rhossiliensis OWVT-1 clustered with the serine proteases of parasites of nematode eggs rather than with those of the trapping fungi.

The living strategy of nematophagous fungi

The infection structures, trophism, and ecological character of nematophagous fungi are reviewed in this article on the basis of data extracted from the literature and the most recent experiments conducted in this area. Traditionally, nematophagous fungi are classified into four groups according to their modes of attacking nematodes: nematode-trapping fungi using adhesive or mechanical hyphal traps, endoparasitic fungi using their spores, eggparasitic fungi invading nematode eggs or females with their hyphal tips, and toxin-producing fungi immobilizing nematodes before invasion. In the present review, we focus on the first two groups. The living strategies of these nematophagous fungi depend on the diversity of their infection structures, such as different traps and spore types, which determine the modes of infecting nematodes. The diversity of trophic modes of nematophagous fungi is an important prerequisite for fungal survival and activity in soil. The abundance and activity of Hirsutella rhossiliensis and H. minnesotensis, representatives of endoparasites and potential biocontrol agents against nematodes, are highly dependent on environmental factors. Comprehensive understanding of the survival and activity of nematophagous fungi in soil is fundamental for the exploitation of these fungi as successful biocontrol agents.