Horizontal transfer of genetic elements in the black Aspergilli

The thesis deals with the horizontal transfer of genetic elements in the black Aspergilli . The black Aspergilli form a complex group of asexual species. All share a characteristic black conidiospore color and the ability to efficiently degrade tannin. Selective isolation of all different black Aspergillus types is possible on media with 20% tannin. Tannins can form complexes with proteins, that are difficult to mineralize. Therefore, the strains may have a special niche in the control of the natural nitrogen cycle. Black Aspergilli occur worldwide and especially in warmer regions at high densities. The spores have an efficient aerial distribution, which produces a well-mixed sporebank in soil throughout the world.Under laboratory conditions isogenic lines are capable, after hyphal fusions, to form a heteroplasmic heterokaryon and (transient) diploids. This so-called parasexual cycle can result in recombination via reassortment of chromosomes, mitotic crossing-over and/or exchange of cytoplasmic genetic elements. Most of the natural isolates are heterokaryon incompatible with one another and unable to form a stable heterokaryon. About the exact mechanism of the heterokaryon incompatibility reactions in the black Aspergilli little is known. Confrontations between heterokaryon self-incompatible strains suggest that prefusion genes are involved. The fact that protoplast fusions are partly able to overcome incompatibility reactions suggests that also fusion and postfusion genes are involved.One of the cytoplasmic candidates for horizontal transfer is the mitochondrion. Different mitochondrial haplotypes can be distinguished, corresponding with different black Aspergillus types . No horizontal transfer or recombination of mitochondria was observed in our natural isolates, though in protoplast fusions mitochondria can recombine. In nature new mitochondrial types may result from mutations.Most of the transfer experiments in these thesis were done with cytoplamsic dsRNA mycoviruses. In nature 10% of the population is infected with a variety of different dsRNA fragments of different viral origins. These mycoviruses can cause serious reductions in their host's fitness on traits as spore production and growth rate. Population genetic models predict that deleterious elements should disappear from a population, unless they have an extra way of transfer than just vertical transmission to offspring. Interspecies transfer of mycoviruses with species like Fusarium poae was in our experiments less difficult to achieve (and thus perhaps more likely in nature) than intraspecies transfer between different black Aspergillus types.In a diploid both interchromosomal and intrachromosomal mitotic recombination could take place. However, molecular data suggests that there is little (para)sexual recombination in the black Aspergillus population, in contrast to other presumably asexual fungi tested so far. Recently transposable elements have been found in black Aspergillus strains. These do seem to have transposed between different, quite unrelated strains. Circular intermediates of these transposable elements may also transfer little parts of genomic DNA, which may lead to some recombination. The size of the genetic elements may influence the chance on horizontal transfer during cell contact: no detectable transfer of mitochondria, very little of mycoviruses and some transfer of transposable elements.</p

ToxGen: An improved reference database for the identification of type B-trichothecene genotypes in Fusarium

Type B trichothecenes, which pose a serious hazard to consumer health, occur worldwide in grains. These mycotoxins are produced mainly by three different trichothecene genotypes/chemotypes: 3ADON (3-acetyldeoxynivalenol), 15ADON (15-acetyldeoxynivalenol) and NIV (nivalenol), named after these three major mycotoxin compounds. Correct identification of these genotypes is elementary for all studies relating to population surveys, fungal ecology and mycotoxicology. Trichothecene producers exhibit enormous strain-dependent chemical diversity, which may result in variation in levels of the genotype´s determining toxin and in the production of low to high amounts of atypical compounds. New high-throughput DNA-sequencing technologies promise to boost the diagnostics of mycotoxin genotypes. However, this requires a reference database containing a satisfactory taxonomic sampling of sequences showing high correlation to actually produced chemotypes. We believe that one of the most pressing current challenges of such a database is the linking of molecular identification with chemical diversity of the strains, as well as other metadata. In this study, we use the Tri12 gene involved in mycotoxin biosynthesis for identification of Tri genotypes through sequence comparison. Tri12 sequences from a range of geographically diverse fungal strains comprising 22 Fusarium species were stored in the ToxGen database, which covers descriptive and up-to-date annotations such as indication on Tri genotype and chemotype of the strains, chemical diversity, information on trichothecene-inducing host, substrate or media, geographical locality, and most recent taxonomic affiliations. The present initiative bridges the gap between the demands of comprehensive studies on trichothecene producers and the existing nucleotide sequence databases, which lack toxicological and other auxiliary data. We invite researchers working in the fields of fungal taxonomy, epidemiology and mycotoxicology to join the freely available annotation effort.Fil: Kulik, Tomasz. Uniwersytet Warminsko-mazurski W Olsztynie;Fil: Abarenkov, Kessy. University Of Tartu.; EstoniaFil: Busko, Maciej. Poznań University of Life Sciences; PoloniaFil: Bilska, Katarzyna. University of Warmia and Mazury; PoloniaFil: van Diepeningen, Anne D.. University of Amsterdam; Países BajosFil: Ostrowska-Kolodziejczak, Anna. Poznań University of Life Science; PoloniaFil: Krawczyk, Katarzyna. University of Warmia and Mazur; PoloniaFil: Brankovics, Balázs. CBS-KNAW Fungal Biodiversity Centre; Países Bajos. University of Amsterdam; Países BajosFil: Stenglein, Sebastian Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Cientifico Tecnolológico Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología. Laboratorio de Biología Funcional y Biotecnología; ArgentinaFil: Sawicki, Jakub. University of Warmia and Mazury; PoloniaFil: Perkowski, Juliusz. Poznań University of Life Sciences; Poloni

Growth and hydrolase profiles can be used as characteristics to distinguish Aspergillus niger and other black aspergilli

Wild type Aspergillus niger isolates from different biotopes from all over the world were compared to each other and to the type strains of other black Aspergillus species with respect to growth and extracellular enzyme profiles. The origin of the A. niger isolate did not result in differences in growth profile with respect to monomeric or polymeric carbon sources. Differences were observed in the growth rate of the A. niger isolates, but these were observed on all carbon sources and not specific for a particular carbon source. In contrast, carbon source specific differences were observed between the different species. Aspergillus brasiliensis is the only species able to grow on D-galactose, and A. aculeatus had significantly better growth on Locus Bean gum than the other species. Only small differences were found in the extracellular enzyme profile of the A. niger isolates during growth on wheat bran, while large differences were observed in the profiles of the different black aspergilli. In addition, differences were observed in temperature profiles between the black Aspergillus species, but not between the A. niger isolates, demonstrating no isolate-specific adaptations to the environment

Calendar 2012

Background Fusarium species are among the most common fungi present in the environment and some species have emerged as major opportunistic fungal infection in human. However, in immunocompromised hosts they can be virulent pathogens and can cause death. The pathogenesis of this infection relies on three factors: colonization, tissue damage, and immunosuppression. A novel Fusarium species is reported for the first time from keratitis in an agriculture worker who acquired the infection from plant material of maize. Maize plants are the natural host of this fungus where it causes stalk rot and seeding malformation under temperate and humid climatic conditions. The clinical manifestation, microbiological morphology, physiological features and molecular data are described.MethodsDiagnosis was established by using polymerase chain reaction of fungal DNA followed by sequencing portions of translation elongation factor 1 alpha (TEF1 ¿) and beta-tubulin (BT2) genes. Susceptibility profiles of this fungus were evaluated using CLSI broth microdilution method.ResultsThe analyses of these two genes sequences support a novel opportunist with the designation Fusarium temperatum. Phylogenetic analyses showed that the reported clinical isolate was nested within the Fusarium fujikuroi species complex. Antifungal susceptibility testing demonstrated that the fungus had low MICs of micafungin (0.031 ¿g/ml), posaconazole (0.25 ¿g/ml) and amphotericin B (0.5 ¿g/ml).ConclusionThe present case extends the significance of the genus Fusarium as agents of keratitis and underscores the utility of molecular verification of these emerging fungi in the human host

Interspecies virus transfer via protoplast fusions between Fusarium poae and black Aspergillus strains

Similarities between the genome organisation of dsRNA mycoviruses and dsRNA patterns in different fungal species suggest a relatedness between these viruses, which could be the result of co-evolved infections or of interspecies transfer. Such interspecies transfer between species is suggested by our observation of transfer and maintenance of mycoviral dsRNAs between Fusarium and Aspergillus via protoplast fusion

Emerging pan-resistance in <i>Trichosporon </i>species:a case report

BACKGROUND: Trichosporon species are ubiquitously spread and known to be part of the normal human flora of the skin and gastrointestinal tract. Trichosporon spp. normally cause superficial infections. However, in the past decade Trichosporon spp. are emerging as opportunistic agents of invasive fungal infections, particularly in severely immunocompromised patients. Clinical isolates are usually sensitive to triazoles, but strains resistant to multiple triazoles have been reported. CASE PRESENTATION: We report a high-level pan-azole resistant Trichosporon dermatis isolate causing an invasive cholangitis in a patient after liver re-transplantation. This infection occurred despite of fluconazole and low dose amphotericin B prophylaxis, and treatment with combined liposomal amphotericin B and voriconazole failed. CONCLUSION: This case and recent reports in literature show that not only bacteria are evolving towards pan-resistance, but also pathogenic yeasts. Prudent use of antifungals is important to withstand emerging antifungal resistance

Efficient degradation of tannic acid by black Aspergillus species

A set of aspergillus strains from culture collections and wild-type black aspergilli isolated on non-selective media were used to validate the use of media with 20 % tannic acid for exclusive and complete selection of the black aspergilli. The 20% tannic acid medium proved useful for both quantitative and qualitative selection of all different black aspergilli, including all recognized species: A. carbonarius, A. japonicus, A. aculeatus, A foetidus, A. heteromorphus, A. niger, A. tubingensis and A. brasiliensis haplotypes. Even higher concentrations of tannic acid can be utilized by the black aspergilli suggesting a very efficient tannic acid-degrading system. Colour mutants show that the characteristic ability to grow on high tannic acid concentrations is not causally linked to the other typical feature of these aspergilli, i.e. the formation of brown-black pigments. Sequence analysis of the A. niger genome using the A. orvzae tannase gene yielded eleven tannase-like genes, far more than in related species. Therefore, a unique ecological niche in the degradation of tannic acid and connected nitrogen release seems to be reserved for these black-spored cosmopolitans

Diversity of Mobile Genetic Elements in the Mitogenomes of Closely Related Fusarium culmorum and F. graminearum sensu stricto Strains and Its Implication for Diagnostic Purposes

Much of the mitogenome variation observed in fungal lineages seems driven by mobile genetic elements (MGEs), which have invaded their genomes throughout evolution. The variation in the distribution and nucleotide diversity of these elements appears to be the main distinction between different fungal taxa, making them promising candidates for diagnostic purposes. Fungi of the genus Fusarium display a high variation in MGE content, from MGE-poor (Fusarium oxysporum and Fusarium fujikuroi species complex) to MGE-rich mitogenomes found in the important cereal pathogens F. culmorum and F. graminearum sensu stricto. In this study, we investigated the MGE variation in these latter two species by mitogenome analysis of geographically diverse strains. In addition, a smaller set of F. cerealis and F. pseudograminearum strains was included for comparison. Forty-seven introns harboring from 0 to 3 endonucleases (HEGs) were identified in the standard set of mitochondrial protein-coding genes. Most of them belonged to the group I intron family and harbored either LAGLIDADG or GIY-YIG HEGs. Among a total of 53 HEGs, 27 were shared by all fungal strains. Most of the optional HEGs were irregularly distributed among fungal strains/species indicating ancestral mosaicism in MGEs. However, among optional MGEs, one exhibited species-specific conservation in F. culmorum. While in F. graminearum s.s. MGE patterns in cox3 and in the intergenic spacer between cox2 and nad4L may facilitate the identification of this species. Thus, our results demonstrate distinctive traits of mitogenomes for diagnostic purposes of Fusaria