Harpellales (Trichomycetes); mycobionts of insecta

Summary

Species of fungi assigned to the Harpellales, Trichomycetes, occur obligately associated with Insecta. Their possession of monosporous merosporangia (trichospores), zygospores, and crosswalls flared around a plugged central pore augurs for close phyletic affinity with the Kickxellales (Zygomycota). Somatic and reproductive thalli occur attached to the cuticle lining the mid- and hindguts of aquatic dipteran larvae and hindguts of ephemeropteran and plecopteran nymphs. This stage is considered commensalistic. In some species a pathogenic stage of the Harpellales is associated with the ovaries and reduces fecundity. At oviposition fungal spores are deposited by the imago at the sites of new larval populations and provide the primary inoculum.     

Molecular phylogeny of parasitic zygomycota (Dimargaritales, zoopagales) based on nuclear small subunit ribosomal DNA sequences

We analyzed sequence data of the 18S rDNA gene from representatives of nine mycoparasitic or zooparasitic genera to infer the phylogenetic relationships of these fungi within the Zygomycota. Phylogenetic analyses identified a novel monophyletic clade consisting of the Zoopagales, Kickxellales, Spiromyces, and Harpellales. Analyses also identified a monophyletic mycoparasitic-zooparasitic Zoopagales clade in which Syncephalis, Thamnocephalis, and Rhopalomyces form a sister group to a Piptocephalis-Kuzuhaea clade. Although monophyly of the mycoparasitic Dimargaritales received strong bootstrap and decay index support, phylogenetic relationships of this order could not be resolved because of the unusually high rate of base substitutions within the 18S rDNA gene. Overall, the 18S gene tree topology is weak, as reflected by low bootstrap and decay index support for virtually all internal nodes uniting ordinal and superordinal taxa. Nevertheless, the 18S rDNA phylogeny is mostly consistent with traditional phenotypic-based classification schemes of the Fungi.     

Prevalence of Harpellales from Chironomidae larvae in phytotelmata from punta Lara Forest, Argentina

Harpellales (Zygomycota: Trichomycetes) fungi are cosmopolitan obligate inhabitants of the gut of immature insects. A biweekly survey of gut fungi associated with chironomid (Chironomidae: Diptera) larvae living in the impounded water from Eryngium cabrerae (Apiaceae) phytotelmata from Punta Lara forest, Argentina, was done Jan 2003-Dec 2004. Two species of Harpellales were associated with chironomid larvae, Smittium phytotelmatum in the hindgut of Polypedilum sp. and Stachylina lentica in the midgut of both Polypedilum sp. and Metriocnemus eryngiotelmatus. No statistically significant differences were recorded in the prevalence of these Harpellales between seasons. Environmental variables (temperature, rainfall and relative humidity), impounded water volume, pH and chironomid larval density did not have an effect on the prevalence of the Trichomycetes.     

Trichomycetes (Zygomycota) in the digestive tract of arthropods in Amazonas, Brazil

Eight species of Harpellales and three species of Eccrinales (Zygomycota: Trichomycetes) were found associated with the digestive tract of arthropods from terrestrial and aquatic environments in the central Amazon region of Brazil. New species of Harpellales include: Harpella amazonica, Smittium brasiliense, Genistellospora tropicalis in Simuliidae larvae and Stachylina paucispora in Chironomidae larvae. Axenic cultures of S. brasiliense were obtained. Probable new species of Enterobryus (Eccrinales), Harpella, and Stachylina (Harpellales) are described but not named. Also reported are the previously known species of Eccrinales, Passalomyces compressus and Leidyomyces attenuatus in adult Coleoptera (Passalidae), and Smittium culisetae and Smittium aciculare (Harpellales) in Culicidae and Simuliidae larvae, respectively. Comments on the distribution of some of these fungi and their hosts in the Neotropics are provided.     

Evolutionary relationships among basal fungi (Chytridiomycota and Zygomycota): Insights from molecular phylogenetics

Evolutionary relationships of the two basal fungal phyla Chytridiomycota and Zygomycota are reviewed in light of recent molecular phylogenetic investigation based on rDNA (nSSU, nLSU rDNA), entire mitochondrial genomes, and nuclear protein coding gene sequences (e.g., EF-1alpha, RPB1). Accumulated molecular evidence strongly suggests that the two basal fungal phyla are not monophyletic. For example, the chytridiomycete order Blastocladiales appears to be closely related to the zygomycete order Entomophthorales. Within the Zygomycota, a monophyletic clade, consisting of the Dimargaritales, Harpellales, and Kickxellales, which is characterized by a shared unique septal ultrastructure, was identified. Moreover, evidence for the exclusion of zygomycete orders Amoebidiales and Eccrinales from the Fungi, and their placement at the Animal-Fungi boundary has been clearly documented. Microsporidia, a group of amitochondriate organisms currently under intensive study, is not supported as derived within the Fungi, but a fungal affinity cannot be ruled out. Taking these molecular phylogenetic studies into account, we proposed a hypothetical evolutionary framework of basal fungi.     

Eccrinales (Trichomycetes) are not fungi, but a clade of protists at the early divergence of animals and fungi

The morphologically diverse orders Eccrinales and Amoebidiales have been considered members of the fungal class Trichomycetes (Zygomycota) for the last 50 years. These organisms either inhabit the gut or are ectocommensals on the exoskeleton of a wide range of arthropods--Crustacea, Insecta, and Diplopoda--in varied habitats. The taxonomy of both orders is based on a few micromorphological characters. One species, Amoebidium parasiticum, has been axenically cultured and this has permitted several biochemical and phylogenetic analyses. As a consequence, the order Amoebidiales has been removed from the Trichomycetes and placed in the class Mesomycetozoea. An affinity between Eccrinales and Amoebidiales was first suggested when the class Trichomycetes was erected by Duboscq et al. [Arch. Zool. Exp. Gen. 86 (1948) 29]. Subsequently, molecular markers have been developed to study the relationship of these orders to other groups. Ribosomal gene (18S and 28S) sequence analyses generated by this study do not support a close association of these orders to the Trichomycetes or to other fungi. Rather, Eccrinales share a common ancestry with the Amoebidiales and belong to the protist class Mesomycetozoea, placed at the animal-fungi boundary.     

Molecular phylogeny of Zygomycota based on EF-1alpha and RPB1 sequences: limitations and utility of alternative markers to rDNA

Earlier molecular phylogenetic analyses based on nuclear small subunit ribosomal DNA (nSSU rDNA) suggest that the Zygomycota are polyphyletic within the Chytridiomycota. However, these analyses failed to resolve almost all interordinal relationships among basal fungi (Chytridiomycota and Zygomycota), due to lack of sufficient characters within the nSSU rDNA. To further elucidate the higher-level phylogeny of Zygomycota, we have sequenced partial RPB1 (DNA dependent RNA polymerase II largest subunit) and EF-1alpha (translation elongation factor 1 alpha) genes from 10 and 3 zygomycete fungi, respectively. Independent molecular phylogenetic analyses were performed based on each sequence by distance and maximum likelihood methods. Although deep phylogenetic relationships among basal fungi still remain poorly resolved using either gene, the RPB1-based phylogeny identified a novel monophyletic clade consisting of the Dimargaritales, Harpellales, and Kickxellales. This result suggests that regularly formed septa (cross walls that divide hyphae into segments) with a lenticular cavity are plesiomorphic for this clade, and indicates the importance of septal pore ultrastructure in zygomycete phylogeny. In addition, a peculiar mucoralean genus Mortierella, which was considered to be distantly related to the other Mucorales based on previous nSSU rDNA analyses, was resolved as the basal most divergence within the Mucorales, consistent with traditional phenotypic-based taxonomy. Although the taxa included in our analysis are restricted, the monophyly of each order suggested by nSSU rDNA phylogeny is supported by the present RPB1-based analysis. These results support the potential use of RPB1 as an alternative marker for fungal phylogenetic studies. Conversely, the overall fungal phylogeny based on EF-1alpha sequence is poorly resolved. A comparison of numbers of observed substitutions versus inferred substitutions within EF-1alpha indicates that this gene is much more saturated than RPB1. This result suggests that the EF-1alpha gene is unsuitable for resolving higher-level phylogenetic relationships within the Fungi.     

Pathogenic fungi of insects from Argentina (Zygomycetes: Entomophthorales)

Pathogenic fungi of insects from Argentina (Zygomycetes: Entomophthorales). Three species of Entomophthorales entomopathogenic fungi (Zygomycotina: Zygomycetes) have been identified from insects in agricultural crops (Buenos Aires Province, Argentina): Zoophthora radicans Batko (Brefeld); Entomophthora planchoniana Cornu and Pandora gammae (Weiser) Humber. Fungal structure measurements are reported.     

Trichomycete gut fungi from tropical regions of the world

Fifty-nine species of gut fungi in the orders Harpellales and Asellariales, Class Trichomycetes, have been collected in eight tropical regions of the world, some species occurring in more than one geographic region. Regarding the Harpellales, the rather low number of taxa, compared to reports in more temperate localities, is due primarily to relatively few collections in the tropics, as well as the usually warmer waters found in tropical regions that often have a lower species richness of potential immature insect hosts. Asellariales in freshwater, marine, and terrestrial habitats, likewise, have been seldom inventoried in the tropics. Nonetheless, it is clear that the tropics are fertile grounds for discovering new genera and species, and future investigations will undoubtedly reveal many new taxa that will lead to a better understanding of the evolution and biogeography of Trichomycetes.     

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.     

Opportunistic zygomycotic infections

This is a literature review of 361 opportunistic fungal infections caused by the Zygomycetes. The clinical and laboratory diagnosis, pathogenesis, management, treatment, and outcome of infection are discussed. The Zygomycetes are a group of opportunistic fungi (orders Mucorales and Entomophthorales) which cause severe infections which may be fatal. Early clinical recognition, prompt diagnostic procedures, control of underlying disease and treatment with high doses of amphotericin B and aggressive surgery increases survival in an otherwise lethal infection.     

Harpellales in the digestive tracts of Ephemeroptera and Plecoptera nymphs from Veracruz, Mexico

This is the first report of Harpellales (Zygomycota) from Mexico, including herein only the endosymbiotic species of gut fungi in the digestive tracts or shed exuviae of Plecopteran and Ephemeropteran nymphs. Four new species are described: Allantomyces zopilotei, Bojamyces olmecensis, Gauthier-omyces viviparus and Graminella ophiuroidea. Among previously known Harpellales, Lancisporomyces nemouridarum and Zygopolaris ephemeridarum are southern range extremes and new records for Mexico. All species are illustrated and discussed relating to biogeographic implications of the new reports from Mexico, as well as the particular environmental circumstances of the Harpellales in the tropics.     

First report of a trichomycete fungus (Zygomycota: Trichomycetes) inhabiting larvae of Simulium ochraceum sensu lato Walker (Diptera: Simuliidae) from the Galapagos Islands

A collection of the larval black fly Simulium ochraceum sensu lato Walker was made at six lotic habitats on San Cristobal Island, Galapagos Islands, Ecuador, during May 2003. Sixty-eight larvae were assayed for the presence of gut fungi (Zygomycota: Trichomycetes). A trichomycete, designated as Smittium sp. was found inhabiting the hindgut of 17.6% of S. ochraceum s.l. larvae. Implications of this finding with respect to both host and trichomycete biogeography are discussed.     

Trifoliellum bioblitzii, a new genus of trichomycete from mayfly nymphs in Nova Scotia, Canada

Trichomycetes are an ecological group of fungi and protists that colonize the gut lining of invertebrates in aquatic and moist terrestrial habitats. The diversity of this group appears to be high with many new species discovered each year. A new genus of fungal trichomycete, Trifoliellum (Harpellales), is described here with the type species T. bioblitzii. This genus is characterized by having unique, trefoil-shaped asexual spores (trichospores). Another new species, Legeriosimilis halifaxensis, also is described from the same mayfly host, Eurylophella temporalis, collected from the same site near Halifax, Nova Scotia.     

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.     

Trichomycetes living in the guts of aquatic insects of Misiones and Tierra del Fuego, Argentina

Fourteen species of Trichomycetes living in the guts of aquatic insects are reported from two provinces of Argentina, Misiones and Tierra del Fuego. Twelve of the species belong to the Harpellales and two are Amoebidiales. Five harpellid species are reported from Misiones in the extreme northeast of the country (Genistellospora homothallica, Harpella tica, Smittium culisetae, Smittium sp., Stachylina sp.) and seven are from Tierra del Fuego, the southern tip of South America (H. meridianalis, Glotzia sp., S. culicis, S. cellaspora, S. imitatum, Stachylina minima, Penella simulii). Insect hosts all were immature stages of Culicidae, Simuliidae, Chironomidae, Ceratopogonidae (Insecta: Diptera), and Ephemeroptera and Plecoptera. The lower diversity of Trichomycetes found at Misiones, which has a subtropical climate and rainforest vegetation, was due possibly to the warmer temperatures of the water (15-24 C), compared to the colder streams of Tierra del Fuego (9-15 C), with forests and steppes as typical vegetation.     

Ramicandelaber, a new genus of the Kickxellales, Zygomycetes

Ramicandelaber, a new genus of Zygomycetes is erected to accommodateRamicandelaber longisporus sp. nov. The fungus has hyphal septa with median plugs and forms homologous structures to sporocladia and pseudophialides. These characteristics suggest that it belongs to the Kickxellales, Zygomycetes.     

Dacryodiomyces, a new genus of Harpellales in Chironomidae larvae

A new genus of gut fungus in the Harpellales (Trichomycetes) with the type species Dacryodiomyces oklahomensis, found in Chironomidae larvae, is described from northeastern Oklahoma, USA. The most distinguishing characters are the elongate-ovoid zygospores attached to their zygosporophore at one end (Type IV), together with trichospores bearing a collar and a single appendage.