Mycological research最新文献

The entomopathogenic fungi Zoophthora radicans and Pandora blunckii co-occur in field populations of Plutella xylostella and, therefore, are likely to interact during the infection process. We have investigated the possible outcomes of these interactions in the laboratory. Using four isolates, two of each fungal species, inter-specific interaction experiments were done in Petri dishes and on intact plants. In Petri dish experiments, larvae were inoculated directly using sporulating mats of mycelium, both species had the same opportunity to infect and only the relative concentration of conidia of each pathogen species applied was manipulated. In the intact plant experiments, larvae were placed onto fungus-contaminated plants, inoculation was passive and the probability of infection by either or both species of fungi depended on larval activity and proximity to inoculum. In the Petri dish experiment, the species with the largest concentration of conidia out-competed the other regardless of virulence, and results were similar in the intact plant experiment. The ecological implications for competition or co-existence of these two pathogens in the field are discussed.

Tricladium, with 21 accepted species, is the largest genus of aquatic hyphomycetes. It encompasses species with dematiaceous as well as mucedinaceous colonies. Conidiogenesis is thalloblastic; conidiogenous cells proliferate percurrently or sympodially. Conidia have typically two alternate primary lateral branches. Fontanospora and Variocladium are segregates of Tricladium, differing by conidial branching. Varicosporium comprises nine species, one not well known. Conidiogenesis is blastic or thalloblastic, conidiogenous cells proliferate sympodially or are determinate; conidia regularly produce primary and secondary branches and often fragment into part conidia. Molecular analyses on the 28S rDNA of 86 isolates, including 16 species of Tricladium, five species of Varicosporium, two species of Fontanospora and one species of Variocladium, place these hyphomycetes within Helotiales. Tricladium is polyphyletic and placed in six clades; Varicosporium is polyphyletic and placed in three clades; Fontanospora is polyphyletic within a single clade. Variocladium is placed with poor support as a sister taxon to Varicosporium giganteum, Hymenoscyphus scutula and Torrendiella eucalypti.

Fungal surface hydrophobicity has many ecological functions and water contact angles measurement is a direct and simple approach for its characterization. The objective of this study was to evaluate if in-vitro growth conditions coupled with versatile image analysis allows for more accurate fungal contact angle measurements. Fungal cultures were grown on agar slide media and contact angles were measured utilizing a modified microscope and digital camera setup. Advanced imaging software was adopted for contact angle determination. Contact angles were observed in hydrophobic, hydrophilic and a newly created chronoamphiphilic class containing fungi taxa with changing surface hydrophobicity. Previous methods are unable to detect slight changes in hydrophobicity, which provide vital information of hydrophobicity expression patterns. Our method allows for easy and efficient characterization of hydrophobicity, minimizing disturbance to cultures and quantifying subtle variation in hydrophobicity.

Interactions of rye (Secale cereale) root border cells (RBCs), generated during plant growth and surrounding the root cap, with nonpathogenic rhizosphere Fusarium culmorum isolates: DEMFc2 (PGPF) and DEMFc5 (DRMO), and a pathogenic strain DEMFc37 were studied in test tube experiments. The effect of water-suspended RBCs released from the rye root cap on the rate of macroconidia germination and hyphae (mycelial) growth of F. culmorum strains was also examined. It was found that root caps of 3-d-old rye seedlings (with the root length of 20 mm) were surrounded with a layer of RBCs generated in a number specific for this plant species of 1980 ± 30. Introduction of the macroconidia of the tested F. culmorum strains into the root zone of 3-d-old seedlings resulted, after 3 d of incubation, in the formation of mantle-like structures only in the rhizosphere of plants inoculated with the pathogenic DEMFc37 strain. The macroconidia were suspended in (1) water, (2) a water mixture with root caps deprived of RBCs, (3) Martin medium, (4) malt extract broth, and (5) a water mixture with rye RBCs, and their percentage germination was determined during 96-h incubation at 20 °C. Germination of the macroconidia of all the tested F. culmorum strains suspended in the rich growth media (Martin and malt extract broth) and in the mixture with RBCs was significantly speeded up. While only an average of 16.6 % of macroconidia suspended in water germinated after 96-h incubation, more than 90 % of those suspended in the growth media or in the mixture with RBCs germinated after 24 h of incubation. In all the treatments, the highest rate of macroconidia germination was found in suspensions of the pathogenic strain and the lowest in macroconidial suspensions of the PGPF strain. The stimulatory effect of RBCs was not specific to the pathogenic strain. Nevertheless, microscopic observation revealed that it was only in the suspension containing a mixture of rye RBCs and macroconidia of the pathogenic strain that after 48-h incubation compact clusters of hyphae and RBCs, resembling mantle-like structures found in the root zone of plants inoculated only with the pathogenic strain but not inoculated with DRMO and PGPF strain, were formed.

Aureobasidium pullulans is the source of the commercially valuable polysaccharide pullulan and the enzyme xylanase. Isolates are typically off-white to pale pink or black on solid media, while some tropical isolates have been described as ‘color variants’ with bright pigments of red, yellow or purple. We sequenced 5 loci (internal transcribed spacer, intergenic spacer 1, translation elongation factor-1 alpha, beta tubulin, and RNA polymerase II) from 45 new isolates from Thailand. Based on the phylogenetic analyses, isolates were classified into 12 clades. Each clade showed different colors on different culture media including two clades with ‘color variants’ and some clades exhibited high levels of pullulan production or xylanase activity. Colony characteristics do not correlate perfectly with DNA sequence phylogeny or the physiological characters, but DNA sequence differences rapidly identify isolates with genetic novelty.

Fully subterranean Rhizanthella gardneri (Orchidaceae) is obligately mycoheterotrophic meaning it is nutritionally dependent on the fungus it forms mycorrhizas with. Furthermore, R. gardneri purportedly participates in a nutrient sharing tripartite relationship where its mycorrhizal fungus simultaneously forms ectomycorrhizas with species of Melaleuca uncinata s.l. Although the mycorrhizal fungus of R. gardneri has been morphologically identified as Thanatephorus gardneri (from a single isolate), this identification has been recently questioned. We sought to clarify the identification of the mycorrhizal fungus of R. gardneri, using molecular methods, and to identify how specific its mycorrhizal relationship is. Fungal isolates taken from all sites where R. gardneri is known to occur shared almost identical ribosomal DNA (rDNA) sequences. The fungal isolate rDNA most closely matched that of other Ceratobasidiales species, particularly within the Ceratobasidium genus. However, interpretation of results was difficult as we found two distinct ITS sequences within all mycorrhizal fungal isolates of R. gardneri that we assessed. All mycorrhizal fungal isolates of R. gardneri readily formed ectomycorrhizas with a range of M. uncinata s.l. species. Consequently, it is likely that R. gardneri can form a nutrient sharing tripartite relationship where R. gardneri is connected to autotrophic M. uncinata s.l. by a common mycorrhizal fungus. These findings have implications for better understanding R. gardneri distribution, evolution and the ecological significance of its mycorrhizal fungus, particularly in relation to nutrient acquisition.

The spatial distribution of basidiocarps provides much information on the dispersal abilities, habitat preferences, and inter- and intraspecific interactions of aphyllophoraceous fungi. To reveal the spatial distribution and resource utilization patterns of aphyllophoraceous fungi in Malaysia, we conducted field observations in a primary forest in 2006 and analyzed the relationships between the abundance of eight dominant fungal species and various environmental factors. The topographical characteristics were significantly patchily distributed at the 100-m scale, whereas woody debris and most fungal species were distributed randomly. Although the dominant fungal species differed among the decay classes and diameters of the woody debris, the abundance of a few dominant species was significantly correlated with environmental factors. Although the latter factors might affect the spatial distribution of these fungi, the effects appear to be so small that they would not create an aggregated distribution at a few 100-m scales.

The complete sequence of Paracoccidioides brasiliensis CHS5 gene, encoding a putative chitin synthase revealed a 5583 nt open reading frame, interrupted by three introns of 82, 87 and 97 bp (GenBank Accession No EF654132). The deduced protein contains 1861 amino acids with a predicted molecular weight of 206.9 kDa. Both its large size and the presence of a N-terminal region of approx. 800 residues with a characteristic putative myosin motor-like domain, allow us to include PbrChs5 into class V fungal chitin synthases. Sequence analysis of over 4 kb from the 5′ UTR region in CHS5, revealed the presence of a previously reported CHS4 gene in P. brasiliensis, arranged in a head-to-head configuration with CHS5. A motif search in this shared region showed the presence of stress response elements (STREs), three binding sites for the transcription activators Rlm1p (known to be stimulated by hypo-osmotic stress) and clusters of Adr1 (related to glucose repression). A quantitative RT-PCR analysis pointed to changes in transcription levels for both genes following oxidative stress, alteration of external osmolarity and under glucose-repressible conditions, suggesting a common regulatory mechanism of transcription.

Sterile cultured isolates of lichen-forming aposymbionts have not yet been used to investigate lichen–rock interactions under controlled conditions. In this study mycobionts and photobiont of the endolithic lichens Bagliettoa baldensis and Bagliettoa marmorea were isolated and inoculated with coupons of one limestone and four marbles commonly employed in the Cultural Heritage framework. After one year of incubation, microscopic observations of polished cross-sections were performed to verify if the typical colonization patterns observed in the field may be reproduced in vitro and to evaluate the receptivity of the five lithotypes to endolithic lichens. The mycobionts of the two species developed both on the surface of and within all the lithotypes, showing different penetration pathways which depend on mineralogical and structural features and highlight different receptivity. By contrast, algae inoculated with the coupons did not penetrate them. Observations suggest that the hyphal penetration along intrinsic discontinuities of rocks is a relatively fast phenomenon when these organisms are generally considered as slow-growing. Samples from limestone outcrops and abandoned marble quarries, colonized by the same species or other representatives of Verrucariaceae, showed penetration pathways intriguingly similar to those reproduced in vitro and highlighted that lichen-driven erosion processes only increase the availability of hyphal passageways after a long-term colonization. These results show that in vitro incubation of sterile cultured lichen-forming ascomycetes with rock coupons is a practicable experimental system to investigate the lichen–rock interactions under controlled conditions and, together with analysis in situ, may support decisions on conservative treatments of historical and cultural significant stone substrata.

Fungus-growing termites cultivate their mutualistic basidiomycete Termitomyces species on a substrate called a fungal comb. Here, the Suicide Polymerase Endonuclease Restriction (SuPER) method was adapted for the first time to a fungal study to determine the entire fungal community of fungal combs and to test whether fungi other than the symbiotic cultivar interact with termite hosts. Our molecular analyses show that although active combs are dominated by Termitomyces fungi isolated with direct Polymerase Endonuclease Restriction – Denaturing Gradient Gel Electrophoresis (PCR-DGGE), they can also harbor some filamentous fungi and yeasts only revealed by SuPER PCR-DGGE. This is the first molecular evidence of the presence of non-Termitomyces species in active combs. However, because there is no evidence for a species-specific relationship between these fungi and termites, they are mere transient guests with no specialization in the symbiosis. It is however surprising to notice that termite-associated Xylaria strains were not isolated from active combs even though they are frequently retrieved when nests are abandoned by termites. This finding highlights the implication of fungus-growing termites in the regulation of fungi occurring within the combs and also suggests that they might not have any particular evolutionary-based association with Xylaria species.