Isolation of diverse viable fungi from the larvae of the introduced chironomid <Emphasis Type="Italic">Eretmoptera murphyi</Emphasis> on Signy Island

The chironimid midge Eretmoptera murphyi has been introduced to Signy Island and has since become established at a single site. Viable propagules of a diverse range of micro-fungi were recovered from the normal intestinal tract of larvae of E. murphyi, indicating the potential for the larvae to act as vectors for fungal introductions. The fungi present in the intestines of the larvae included ascomycetes, zygomycetes and an oomycete, and this diversity highlights the potential for multiple microbial introductions from a single invertebrate introduction.     

Pythium burgundicum sp. nov. isolated from soil samples taken in French vineyards

During the course of investigation on pythiaceous fungi occurring in the Burgundian vineyards, a new species of Pythium has been isolated. This oomycete is characterized by its nonproliferating and nonsporulating, spherical to cylindrical type of sporangia (hyphal bodies) germinating through germ tubes, smooth-walled oogonia that are supplied with hypogynous, monoclinous or rarely diclinous antheridia, and smooth-walled oospores. The antheridial cells are very prominent and are reminiscent of Pythium bifurcatum, Pythium segnitium and Pythium longandrum described previously by the author. The internal transcribed spacer region of the rRNA of this new species is composed of 883 bases, which is quite different from that of the closest relatives. Morphological and molecular features of this new species, named as Pythium burgundicum , are discussed in this article.     

Cell biology of plant-oomycete interactions

The last 4 years have seen significant advances in our understanding of the cellular processes that underlie the infection of plants by a range of biotrophic and necrotrophic oomycete pathogens. Given that oomycete and fungal pathogens must overcome the same sets of physical and chemical barriers presented by plants, it is not surprising that many aspects of oomycete infection strategies are similar to those of fungal pathogens. A major difference, however, centres on the role of motile oomycete zoospores in actively moving the pathogen to favourable infection sites. Recent studies have shown that the plant defence response to invading oomycetes is similar to that mounted against fungi, but biochemical differences between oomycete and fungal surface molecules must have implications for plant recognition of and defence against oomycete pathogens. The aim of this short review is to provide a cell biological framework within which emerging data on the molecular basis of oomycete-plant interactions may be placed.     

Reassessment of the role of phospholipids in sexual reproduction by sterol-auxotrophic fungi.

Several genera of oomycete fungi which are incapable of de novo sterol synthesis do not require these compounds for vegetative growth. The requirement for an exogenous source of sterols for sexual reproduction by several members of the Pythiaceae has been questioned by reports of apparent induction and maturation of oospores on defined media supplemented with phospholipids in the absence of sterols. A more detailed examination of this phenomenon suggested that trace levels of sterols in the inoculum of some pythiaceous fungi act synergistically with phospholipid medium supplements containing unsaturated fatty acid moieties to induce oosporogenesis. Phospholipid analysis of one species, Pythium ultimum, suggested that only the fatty acid portion of the exogenous phospholipid is taken up by the fungus. Enrichment of the phospholipid fraction of total cell lipid of P. ultimum with unsaturated fatty acids promoted oospore induction, and enhanced levels of unsaturated fatty acids in the neutral lipid fraction increased oospore viability. For some pythiaceous fungi, the levels of sterols required for the maturation of oospores with appropriate phospholipid medium supplementation suggest that these compounds are necessary only for the sparking and critical domain roles previously described in other fungi.     

Symbiotic Harpellales (Trichomycetes) in Tasmanian aquatic insects

Surveys for symbiotic fungi in the guts of aquatic insect larvae (Trichomycetes: Harpellales) in Tasmania, Australia, resulted in the discovery of four new species: two in Gripopterygidae (Plecoptera) nymphs, Plecopteromyces leptoperlarum and P. trinotoperlarum, and two associated with Diptera larvae, Smittium magnosporum in Thaumaleidae and Stachylina dolichospora in Chironomidae. Previously described species of Harpellales from other localities are reported and new host records summarized. A key to all Tasmanian species of Harpellales is provided.     

OBSERVATIONS ON THE BIOLOGY OF CORYMBITES CUPREUS F. (COLEOPTERA, ELATERIDAE)

The life history of Corymbites cupreus F. is described, and its economic importance is assessed from field observations and laboratory experiments. The females are on the wing in May and June, egg-laying takes place in June and the incubation period is about 34 days. The larval stage probably occupies 5 years under field conditions and pupation occurs towards the end of July or beginning of August. The imagines emerge in about 21 days, but they do not always remain in their earthen pupal cells until the following spring as do several other Elaterid species. The larvae feed principally on the roots and underground stems of plants, but they can exist on decayed organic matter in the soil. Individually they are far more injurious to potatoes, wheat, oats, barley and other cultivated crops than those of either Agriotes spp. or Athous niger, but because they are restricted to comparatively high altitudes, they are seldom pests of major importance. Birds and cara-bid larvae readily feed on them and they are also subject to attack by a hymeno-pteran parasite and the fungi, Metarrhizium anisopliae (Metsch) Sor. and Synglio-cladium cleoni (Wize) Petch. All attempts to obtain control of the larvae by the use of these fungi failed.     

New species and first records of trichomycetes from immature aquatic insects in Idaho

Trichomycetes, or gut fungi, are currently recognized as an ecological group of fungi and protists that inhabit the guts of immature insects or other stages and types of arthropods. The geographic distribution of these endosymbionts is worldwide. However trichomycete data from the Pacific Northwest are limited and this is the first account of gut fungi in Idaho. We report on the trichomycetes from a single site, Cottonwood Creek at Military Reserve Park, Boise, Idaho, where periodic surveys for more than a year resulted in the discovery of four newly named, three probably new but unnamed and 15 previously known species. Among the Harpellales three new species, Capniomyces sasquatchoides, Harpella torus and Lancisporomyces lampetriformis, are described, with two possibly new species of Smittium detailed but unnamed at this time pending further collections. A Genistelloides cf. hibernus also is included as a possible new species. One new species of Amoebidiales, Paramoebidium hamatum, is described as well. Hosts in which the gut fungi were recovered include larvae or nymphs of Diptera (Chironomidae and Simuliidae), Ephemeroptera (Baetidae) and Plecoptera (Capniidae and Taeniopterygidae). We hope to demonstrate that future surveys or bioprospecting investigations into the biodiversity of these early-diverging fungi in this region and worldwide remain promising.     

Biological control of Dutch elm disease: Larvicidal activity of Trichoderma harzianum, T. polysporum and Scytalidium lignicola in Scolytus scolytus and S. multistriatus reared in artificial culture

A method is described for the culture of larvae of Scolytus multistriatus and Scolytus scolytus on an artificial medium following exposure to cultures of microorganisms. In control cultures, a natural mortality rate of 21.2% was found for S. multistriatus and 17.6% for S. scolytus. The effects of Trichoderma harzianum, T. polysporum and Scytalidium lignicola on fifth instar larvae of S. scolytus and S. multistriatus reared on the artificial medium were studied. The fungi were larvicidal and larval mortality was increased to more than 80% by inoculation of the larvae with the fungi. Another fungus, Phomopsis oblonga, had little effect on larvae of S. scolytus. The results are discussed in relation to mechanism of pathogenicity of the fungi and their potential use in the control of Dutch elm disease. It is proposed that with modifications, the method is applicable to other bark beetle pests.     

In vivo passage through calves of nematophagous fungi selected for biocontrol of parasitic nematodes.

The experiment was designed to test the survival and performance of stress selected nematophagous fungi after passage through the gastro-intestinal tract of cattle. Ruminating calves were fed daily with a fixed amount of fungal material grown on barley grains. The excreted dung was collected on days four and five after the start of the feeding experiment. Barley grains were washed out of the excreted dung and incoculated on water-agar plates. After incubation for one week, nine of ten fungal isolates were re-isolated from these plates. The predatory capacity of the fungi in the excreted faeces was tested in a dung pat bioassay and a faecal culture system. In the dung pat bioassay, two fungi of the genus Arthrobotrys and six of the genus Duddingtonia reduced the development of Ostertagia ostertagi third stage larvae by 85% (61%-93%), compared to the number of larvae developed from fungus-free control pats. In seven out of these eight isolates, the reduction of larvae in the faecal cultures was 92% (76%-99%).     

Nucleotide sequences of 5S ribosomal RNA from four oomycete and chytrid water molds.

The nucleotide sequences of the 5S rRNAs of the oomycete water molds Saprolegnia ferax and Pythium hydnosporum and of the chytrid water molds Blastocladiella simplex and Phlyctochytrium irregulare were determined by chemical and enzymatic partial degradation of 3' and 5' end-labelled molecules, followed by gel sequence analysis. The two oomycete sequences differed in 24 positions and the two chytrid sequences differed in 27 positions. These pairs differed in a mean of 44 positions. The chytrid sequences clearly most resemble the sequence from the zygomycete Phycomyces, while the oomycete sequences appear to be allied with those from protozoa and slime molds.     

Trafficking arms: oomycete effectors enter host plant cells

Oomycetes cause devastating plant diseases of global importance, yet little is known about the molecular basis of their pathogenicity. Recently, the first oomycete effector genes with cultivar-specific avirulence (AVR) functions were identified. Evidence of diversifying selection in these genes and their cognate plant host resistance genes suggests a molecular "arms race" as plants and oomycetes attempt to achieve and evade detection, respectively. AVR proteins from Hyaloperonospora parasitica and Phytophthora infestans are detected in the plant host cytoplasm, consistent with the hypothesis that oomycetes, as is the case with bacteria and fungi, actively deliver effectors inside host cells. The RXLR amino acid motif, which is present in these AVR proteins and other secreted oomycete proteins, is similar to a host-cell-targeting signal in virulence proteins of malaria parasites (Plasmodium species), suggesting a conserved role in pathogenicity.     

A protein from the mold Aspergillus giganteus is a potent inhibitor of fungal plant pathogens.

A purified preparation of antifungal protein (AFP) from Aspergillus giganteus exhibited potent antifungal activity against the phytopathogenic fungi Magnaporthe grisea and Fusarium moniliforme, as well as the oomycete pathogen Phytophthora infestans. Under conditions of total inhibition of fungal growth, no toxicity of AFP toward rice protoplasts was observed. Additionally, application of AFP on rice plants completely inhibited M. grisea growth. These results are discussed in relation to the potential of the afp gene to enhance crop protection against fungal pathogens in transgenic plants.     

A domain-centric analysis of oomycete plant pathogen genomes reveals unique protein organization

Oomycetes comprise a diverse group of organisms that morphologically resemble fungi but belong to the stramenopile lineage within the supergroup of chromalveolates. Recent studies have shown that plant pathogenic oomycetes have expanded gene families that are possibly linked to their pathogenic lifestyle. We analyzed the protein domain organization of 67 eukaryotic species including four oomycete and five fungal plant pathogens. We detected 246 expanded domains in fungal and oomycete plant pathogens. The analysis of genes differentially expressed during infection revealed a significant enrichment of genes encoding expanded domains as well as signal peptides linking a substantial part of these genes to pathogenicity. Overrepresentation and clustering of domain abundance profiles revealed domains that might have important roles in host-pathogen interactions but, as yet, have not been linked to pathogenicity. The number of distinct domain combinations (bigrams) in oomycetes was significantly higher than in fungi. We identified 773 oomycete-specific bigrams, with the majority composed of domains common to eukaryotes. The analyses enabled us to link domain content to biological processes such as host-pathogen interaction, nutrient uptake, or suppression and elicitation of plant immune responses. Taken together, this study represents a comprehensive overview of the domain repertoire of fungal and oomycete plant pathogens and points to novel features like domain expansion and species-specific bigram types that could, at least partially, explain why oomycetes are such remarkable plant pathogens.     

Fungal and oomycete parasites of Chironomidae,Ceratopogonidae and Simuliidae (Culicomorpha,Diptera)

Members of the families Chironomidae (chironomids or non-biting midges), Ceratopogonidae (ceratopogonids or biting midges) and Simuliidae (simulids or blackflies) are ubiquitous dipterans of the infraorder Culicomorpha. They are extremely diversified in ecological strategies. Their larvae play major roles in aquatic food webs as detritivores or predators, whereas their adults can be general predators (Chironomidae), hemolymphagous or hematophagous predators (Ceratopogonidae and Simuliidae) or pollinators. Both larval and adult stages are commonly infected by bacteria, viruses, protists, nematodes, true fungi and oomycetes. These phylogenetically diverse assemblages of microorganisms can simultaneously infect multiple species of chironomids, ceratopogonids and simulids, and each host may become trophically interrelated with other hosts by sharing their parasites. Here, we review the information on fungal and oomycete parasites of these dipteran groups with special reference to the natural regulation of host populations, the impact of parasitism in food webs, and the potential of these parasites as biocontrol agents.     

Potential role for gut microbiota in cell wall digestion and glucoside detoxification in Tenebrio molitor larvae

Tenebrio molitor larvae were successfully reared free of cultivatable gut lumen bacteria, yeasts and fungi using two approaches; aseptic rearing from surface sterilized eggs and by feeding larvae with antibiotic-containing food. Insects were reared on a rich-nutrient complete diet or a nutrient-poor refractory diet. A comparison of digestive enzyme activities in germ free and conventional insects containing a gut microbiota did not reveal gross differences in enzymes that degrade cell walls from bacteria (lysozyme), fungi (chitinase and laminarinase) and plants (cellulase and licheninase). This suggested that microbial-derived enzymes are not an essential component of the digestive process in this insect. However, more detailed analysis of T. molitor midgut proteins using an electrophoretic separation approach showed that some digestive enzymes were absent and others were newly expressed in microbiota-free larvae. Larvae reared in antibiotic-containing refractory wheat bran diet performed poorly in comparison with controls. The addition of saligenin, the aglycone of the plant glucoside salicin, has more deleterious effects on microbiota-free larvae than on the conventionally reared larvae, suggesting a detoxifying role of midgut microbiota. Analysis of the volatile organic compounds released from the faecal pellets of the larvae shows key differences in the profiles from conventionally reared and aseptically reared larvae. Pentadecene is a semiochemical commonly found in other beetle species. Here we demonstrate the absence of pentadecene from aseptically reared larvae in contrast to its presence in conventionally reared larvae. The results are discussed in the light of the hypothesis that microbial products play subtle roles in the life of the insect, they are involved in the digestion of refractory food, detoxification of secondary plant compounds and modify the volatile profiles of the insect host.     

Plant-ants use symbiotic fungi as a food source: new insight into the nutritional ecology of ant-plant interactions

Usually studied as pairwise interactions, mutualisms often involve networks of interacting species. Numerous tropical arboreal ants are specialist inhabitants of myrmecophytes (plants bearing domatia, i.e. hollow structures specialized to host ants) and are thought to rely almost exclusively on resources derived from the host plant. Recent studies, following up on century-old reports, have shown that fungi of the ascomycete order Chaetothyriales live in symbiosis with plant-ants within domatia. We tested the hypothesis that ants use domatia-inhabiting fungi as food in three ant-plant symbioses: Petalomyrmex phylax/Leonardoxa africana, Tetraponera aethiops/Barteria fistulosa and Pseudomyrmex penetrator/Tachigali sp. Labelling domatia fungal patches in the field with either a fluorescent dye or (15)N showed that larvae ingested domatia fungi. Furthermore, when the natural fungal patch was replaced with a piece of a (15)N-labelled pure culture of either of two Chaetothyriales strains isolated from T. aethiops colonies, these fungi were also consumed. These two fungi often co-occur in the same ant colony. Interestingly, T. aethiops workers and larvae ingested preferentially one of the two strains. Our results add a new piece in the puzzle of the nutritional ecology of plant-ants.