Patterns in the occurrence of saprophytic fungi carried by arthropods caught in traps baited with rotted wood and dung.

Fungi from approximately 1700 individual arthropods that had been captured in traps set in aspen-dominated woodland in western Canada and baited with coyote dung, moose dung, white-rotted wood, brown-rotted wood and fiberglass were isolated in pure culture and identified. These data were analysed with principal components analysis (PCA) to determine whether different types of substrate attracted specific arthropods and whether these animals carried unique assemblages of fungi with known proclivities for the new habitat. Mycobiotic agar was used to restrict the numbers of fungi isolated and resulted in the recovery of 1687 isolates representing 65 species across 12 orders. Isolates of cosmopolitan fungal taxa such as species of Cladosporium, Penicillium, and Beauveria were the most numerous. Taxa with predilections for specific substrates, such as Myxotrichum and Cryptendoxyla that are known inhabitants of cellulose-rich materials (i.e. rotted wood), and various representatives of the keratinophilic Onygenales were recovered from arthropods attracted respectively to baits rich in cellulose and keratin. When traps were analysed according to the identity and numbers of arthropods captured, there was considerable overlap among clusters representing specific bait types, with traps baited with coyote dung being the most divergent partly because they captured significantly more arthropods than those baited with moose dung or rotted wood. When bait type was examined according to the identity and numbers of fungi on trapped arthropods the degree of overlap was also high although a few trends could be discerned. In particular traps baited with brown-rotted wood and coyote dung diverged slightly indicating that arthropods visiting these bait types were carrying somewhat different suites of fungi.

Morphology and development of the reticuloperidial ascomata of Auxarthron conjugatum.

Light and electron microscopy showed that the reticuloperidium of thick-walled hyphae, characteristic of the mature ascoma of Auxarthron conjugaturn, originated from branches that grew from the broad, gyre-like hyphal loops making up the ascomatal initials. Within the developing peridium, short, acropetally proliferating chains of prototunicate asci each arose from a single crozier and matured from base to tip. The walls of young asci were two-layered but evanesced as they matured with the outer layer dissolving before the inner one. Distal asci in some chains retained the inner wall, detached from adjacent asci by septum schizolysis and when transferred to fresh media produced germ tubes and mycelium. Ultraviolet epifluorescent staining with a DNA intercalator (Hoechst) indicated that these spore-like asci probably contained diploid nuclei. In normal asci, ascospores had an inner, electron lucent primary wall and a three-layered secondary wall. The deposition pattern of the middle layer of the secondary wall created the distinctive array of pits and ridges characteristic of the ascospores in this taxon. The production of ascospores, spore-like asci and arthroconidia, along with the tendency of ascospores to adhere in a mass, is interpreted as contributing to the reproductive flexibility and inoculum potential of A. conjugatum. In all respects the ascomata of A. conjugatum differed substantially from the morphologically similar taxon, Myxotrichum arcticum. These findings underscore the benefit of using DNA-based phylogenies in concert with cytological and ultrastructural observations for exploring selective pressures behind homoplasious characters and revealing novel structural features.

Ascomatal morphogenesis in Myxotrichum arcticum supports the derivation of the Myxotrichaceae from a discomycetous ancestor.

Electron microscopy shows that ascomata of Myxotricum arcticum bear a striking resemblance to discocarps in morphogenesis and in previously overlooked aspects of gross morphology. Although mature ascomata of M. arcticum superficially resemble reticuloperidial cleistothecia common in the Onygenales, the bramble-like aggregation of thick-walled hyphae, previously considered to represent a closed peridium, forms a basket-like apothecium that overarches a distinct hymenium of stipitate, protunicate asci interspersed with paraphyses. There is no evidence of asci developing in chains and at different levels as is characteristic of the centrum of many Eurotiomycetes. Instead, more or less globose, stipitate and evanescent asci arise individually from penultimate cells of croziers and develop almost synchronously across a distinct hymenial layer derived from a richly branched network of crozier-bearing hyphae. After dissolution of the ascus wall, ascospores adhere to a membranous sheath that underlies the hymenium. These observations provide strong support for prior suggestions based on molecular phylogenetic comparisons that the Myxotrichaceae recently are derived from a helotialean ancestor. Observations of conidiogenesis show that the typical Oidiodendron anamorph is accompanied by a second conidiogenous form with ampullae and botryose clusters of blastic conidia.

Morphology and phylogenetic placement of Endoconidioma, a new endoconidial genus from trembling aspen.

Endoconidioma populi gen. et sp. nov. is described from black subicula on twigs of trembling aspen, Populus tremuloides, in Alberta, Canada. Pycnidium-like conidiomata are produced on twigs and in culture, but, unlike pycnidia, conidiomata of E. populi have a closed peridium and a locule filled with conidiogenous cells that form conidia endogenously. These endoconidia are hyaline, unicellular and released by the dissolution of the peridial cell wall. In addition to endoconidia, mostly two-celled conidia that form blastically from undifferentiated hyphae occur often in culture but are observed only occasionally on Populus twigs. No coelomycetous taxa have been reported to produce endoconidia, and both the morphological features and DNA sequence data demonstrate that Endoconidioma is distinct from the previously established endoconidial genera. Parsimony analyses of portions of the nuclear ribosomal RNA gene (SSU and ITS) suggest that Endoconidioma is closely related phylogenetically to members of the Dothideales and allied anamorphs in Hormonema and Kabatina.

Endoconidiogenesis in Endoconidioma populi and Phaeotheca fissurella.

Details of the development of endoconidia were basically the same in Endoconidioma populi and Phaeotheca fissurella. In both species, endoconidiogenesis involved (i) subdivision of conidiogenous mother cells by septation to form two to several daughter cells; (ii) accumulation of an electron-dense material between the daughter and mother cell walls; and (iii) separation of the daughter cells by septum schizolysis, accompanied by the dissolution of mother cell wall. Conidiomata of E. populi were unique in having a closed peridium and a locule filled with conidiogenous mother cells and, therefore, we proposed the new term, cleistopycnidium (pl. -a), for this structure. In the cleistopycnidium of E. populi, endoconidiation usually began in the core of the locule and spread outward. Release of endoconidia was by the degeneration of peridial cell walls.

Comparative morphology and phylogenetic placement of two microsclerotial black fungi from Sphagnum.

Capnobotryella renispora and Scleroconidioma sphagnicola form black, irregularly shaped microsclerotia that are indistinguishable in gross morphology on leaves of Sphagnum fuscum. In culture, microsclerotia of these fungi were similar, in that mature component cells possessed thick, highly melanized cell walls, poorly defined organelles, large lipid bodies and simple septa. They were different in morphogenesis, in the way their component cells were organized and in disseminative propagules. Microsclerotia of S. sphagnicola formed phialidic conidiogenous cells on their surface, whereas in C. renispora, adjacent cells in mature microsclerotia often separated from each other by septum schizolysis and formed chlamydospores. The identification of C. renispora from Sphagnum is provisional despite a 100% ITS sequence match with data for a culture derived from the type strain. No holoblastic, reniform conidia typical of the species were formed in nature or in culture, and the SSU sequence for a separately preserved culture of the ex-type strain was markedly divergent. Parsimony analyses of nuclear ribosomal DNA sequences showed that these two fungi were related to separate orders of Dothideomycetes. Both SSU and ITS data supported a close relationship for S. sphagnicola to the Dothideales sensu stricto, while the closest ITS match was to Rhizosphaera spp. In the SSU analyses, C. renispora was nested within the Capnodiales.

Saprobic characteristics of three fungal taxa from ericalean roots and their association with the roots of Rhododendron groenlandicum and Picea mariana in culture.

Simultaneous associations among ectotrophic and ericoid mycorrhizal hosts and their mycorrhizal fungi are expected in boreal bogs where ericaceous shrubs and conifers coexist rooted in an organic matrix dominated by Sphagnum mosses. We were thus prompted to examine, in vitro, the abilities of three ericoid mycorrhizal fungi [ Hymenoscyphus ericae, Oidiodendron maius, and Variable White Taxon (VWT)] to associate with Picea mariana (Pinaceae), with both P. mariana and Rhododendron groenlandicum (Ericaceae) simultaneously, and to decompose Sphagnum fuscum. Hymenoscyphus ericae and VWT developed an intracellular association with roots of P. mariana and with roots of R. groenlandicum. Two strains of O. maius did not form typical infection units in R. groenlandicum, nor did they colonize the root cells of P. mariana. Mass losses incurred by sterilized S. fuscum plants inoculated with these three taxa indicated that O. maius could be more efficient as a free-living saprophyte on this material than either H. ericae or VWT and may in part explain why atypical associations with the roots of ericaceous hosts were formed.

Hydrocarbon-degrading filamentous fungi isolated from flare pit soils in northern and western Canada.

Sixty-four species of filamentous fungi from five flare pits in northern and western Canada were tested for their ability to degrade crude oil using gas chromatographic analysis of residual hydrocarbons following incubation. Nine isolates were tested further using radiorespirometry to determine the extent of mineralization of model radiolabelled aliphatic and aromatic hydrocarbons dissolved in crude oil. Hydrocarbon biodegradation capability was observed in species representing six orders of the Ascomycota. Gas chromatography indicated that species capable of hydrocarbon degradation attacked compounds within the aliphatic fraction of crude oil, n-C12-n-C26; degradation of compounds within the aromatic fraction was not observed. Radiorespirometry, using n-[1-14C]hexadecane and [9-14C]phenanthrene, confirmed the gas chromatographic results and verified that aliphatic compounds were being mineralized, not simply transformed to intermediate metabolites. This study shows that filamentous fungi may play an integral role in the in situ biodegradation of aliphatic pollutants in flare pit soils.

Tetranorditerpene lactones, potent antifungal antibiotics for human pathogenic yeasts, from a unique species of Oidiodendron.

The culture filtrate of a fungus isolated from decaying Picea glauca wood and tentatively identified as Oidiodendron cf. truncatum showed strong antibiotic activity against the pathogenic yeast, Candida albicans. Four new tetranorditerpenoids, oidiodendrolides A (3), B (4), and C (5) and oidiodendronic acid (7) were isolated along with three known tetranorditerpenoids, LL-Z1271 alpha (= PR1387) (1), PR1388 (2), and acrostalidic acid (6), from rice fermented by the above fungus. The structures of oidiodendrolides A (3), B (4), and C (5) and oidiodendronic acid (7) were established on the basis of spectroscopic and chemical investigations. The antifungal activity of the above tetranorditerpenoids against the pathogenic yeasts, Candida albicans and Cryptococcus neoformans is discussed.

Degradation of hydrocarbons in crude oil by the ascomycete Pseudallescheria boydii (Microascaceae).

Four unique strains of Pseudallescheria boydii were isolated from oil-soaked soils in British Columbia and Alberta and compared to strains from cattle dung and raw sewage. Considerable variability in morphology, colony appearance, colony diameter, and temperature tolerance occurred among the strains. They also varied in the sporogenous states produced in culture; all strains had a Scedosporium anamorph and either the Graphium anamorph or cleistothecial teleomorph. Conspecificity of the six isolates was inferred from their morphology and supported by restriction fragment length polymorphism profiles of the internally transcribed spacer region of rDNA and comparing these to Petriella sordida, a similar taxon in the Microascaceae. Three of the strains isolated from oil-contaminated soil and the strain from sewage were tested for their ability to utilize hydrocarbons by incubation with Prudhoe Bay Crude oil as the sole carbon source. Gas chromatographic analysis of the residual oil revealed that the strains isolated from oil-contaminated soil degraded the linear aliphatics. The strain from sewage, previously shown by others to utilize the volatile n-alkanes (i.e., ethane, propane, and butane), did not utilize the liquid saturate compounds. None of the strains was observed to degrade compounds in the aromatic fraction. Pseudallescheria boydii may be an important agent for in situ bioremediation of saturates in oil-contaminated sites.

MYCORRHIZAE AND MYCORRHIZAL FUNGI OF CALYPSO BULBOSA.

The seasonal development and fungal endophytes of the mycorrhizal roots of Calypso bulbosa (L.) Oakes were studied using fresh collections from Alberta and herbarium specimens from six herbaria. Typically, a single pair of mycorrhizal roots are produced at the base of a single corm each growing season. No evidence was found to support the putative existence of a coralloid rhizome in this species. The pattern of fungal infection, peloton formation, and breakdown is similar to other nonsaprophytic, terrestrial orchids. The endophytic fungi of a single mycorrhizal root can belong to a number of different fungal taxa. Fungi isolated and described include Rhizoctonia anaticula Currah, Thanatephorus pennatus Currah, Leptodontidium orchidicola Sigler and Currah, Phialocephala fortinii Wang and Wilcox, and two unnamed isolates of Rhizoctonia.