Introductory Mycology Lecture (PDF)

Introduction to mycology Georgios Tzelepis Senior lecturer Department of Forest Mycology and Plant Pathology SLU January 2025 Course outline (20th – 31th of January) Introduction to mycology Evolution and systemati...

Introduction to mycology Georgios Tzelepis Senior lecturer Department of Forest Mycology and Plant Pathology SLU January 2025 Course outline (20th – 31th of January) Introduction to mycology Evolution and systematics of fungi Genetics and molecular biology of fungi Ecology of fungi Pathogenic fungi part 1 and 2 Pathogenic fungi part 3 Antibiotics, mycotoxins Fungal plant pathogens and beneficial fungi 2 lab exercises (obligatory) 1 seminar presentation (obligatory) 1 key-note speaker seminar (obligatory) Written exams (obligatory) Course Book Medical Microbiology 9th edition by Murray, Rosenthal and Pfaller Section 6: Mycology Questions in the exams will be based on the lectures! Fungi Photo: Georgios Tzelepis Fungi are a group of eukaryotic microorganisms such as yeasts and molds including more 150.000 species It is estimated that 90% of fungal species are unknown (> 3 millions) Photo: Heriberto Velez Fungi ≈ 80% of fungi of medical importance (Aspergillus Candida Pneumocystis etc) Cryptococcus, Malassezia Fungi as pathogens Among the major fungal organisms posing threats to plants and animals are: Batrachochytrium dendrobatidis Magnaporthe oryzae Geomyces destructans Nosema species MC Fisher et al. 2012  Fungi as pathogens Fungal alerts increased between 1995 -2010 Plants Animals There is a continuing positive increase of fungal alerts especially in animal infecting species Fungi compromise the highest threat for species extinction Fungi Increased host loss in the second half of the 20th century MC Fisher et al. 2012  Fungi as pathogens Fungi-host dynamics leading to host extiction: high virulence and mortality rate long-lived environmental stages Georgios Tzelepis broad host range human activities accelerated evolution Fredrik Dölfors MC Fisher et al. 2012  Fungi as human pathogens Fungi are opportunistic human pathogens (There are no nonpathogenic fungi!) Severe infections in immunosuppressed patients They have one of the highest mortality rates (>80%) The population of immunosuppressed patients is increasing globally COVID-19 van de Veerdonket et al. (2017) Georgios Tzelepis Fungi as human pathogens Human pathogenic fungi are only a very small minority of an enormous number of fungal species in the nature For first time WHO lists fungal infection as a global health threat Fungi as human pathogens Fungi as human pathogens Cordyceps species  Fungi as human pathogens Aspergillus spp and Rhizopus spp, causing a life-threatening respiratory disease (mycosis) Aspergillus species have high mortality rate of 30%-95% Mucormycosis (black fungus) associated with COVID-19 in patients with uncontrolled diabetes, with a mortality rate higher than 50%. Vervweij P et al (2020). Georgios Tzelepis Fungi as human pathogens Only four major classes of antifungal drugs Resistance has already been observed Need of new antifungal drugs (urgent!) Georgios Tzelepis  Fungi as plant pathogens Fungi represent the biggest threat for the plants They cause an enormous spectrum of symptoms Powdery mildew Fungal diseases cost American farmers $3.2 billion annually in and cost $158 million annually on fungicide applications Necrotic spots Damping-off Tumours Stunting plants Rust symptoms Fungi as plant pathogens Numerous epidemics of ergotism in Europe between 16th and 18th century caused by the fungus Claviceps purpurea and contains toxic alkaloid similar to LSD.  Fungi as plant pathogens Fungi can result in significant losses in the quality and economic value of fruits and vegetables during transportation, storage, and marketing  Fungi-like organisms as plant pathogens Phytophthora infestans causes the late blight disease in potatoes It is one of the most devastating disease with annual losses > 3 billion/year worldwide P. infestans was responsible for the Great Famine in Ireland between 1845 - 1852 1 million people died and a million more emigrated from Ireland The population fell by 20% - 25% Fungi as friends Fungi are the most important decomposers in nature responsible to break down the dead organic matter and to return nutrients to the soil Fungi form symbiosis with plants (mycorrhiza). They play important roles in nutrient acquisition of plants Fungi as friends Humans have employed fungi for thousands of years. People followed preparative methods that produced their desired products and knew nothing about yeasts made dough rice and fermented cereals Fungi as Friends Fungi as food and medicine More than 1 million tons of Shiitake mushroom produced every year worldwide The white button mushroom is the most popular cultivated with more than 2 million tons They have been used in Asia in traditional medicine for thousand years Fungi as Friends Fungi as food Vegemite is a spread produced from yeast extract Qorn is a meat substitute produced by the fungus Fusarium venetatum Smut fungus is a delicated food in Mexico Fungi as Friends Baking and cheese production The yeast species Saccharomyces cerevisiae is used to ferment dough for more than thousand years Yeast and filamentous species (Kluyveromyces and Penicillium) are used for flavouring and ripening cheeses such as Brie, Camembert, Roquefort etc Fungi as Friends Alcohol production Lack of oxygen or high sugar concentration yeasts produce CO2 and alcohol The yeast species Saccharomyces cerevisiae is used for fermentation in beer and wine Aspergillus species are used for shake production Fungi as friends Drug and antibiotic production The antibiotic penicillin is a powefull antibiotic produced by the species Penicillium It is the first antibiotic discovered on 1928 and saved the life of millions of people Fungi as friends Biofuels Fungi show a tremendous potential for the production of biofuels from a variety of crop plants Yeasts are used for fermentation of sugarcane or corn as a source of bioethanol Basidiomycetes are aslo used for the production of second generation biofuels Fungi as friends Bioremediation Some basidiomycetes have been selected for bioremendation of soil contaminated with organic pollutants. White rot fungi are used for degradation of pesticides and oil polluted the soil Fungi as friends Biopesticides Fungi can be used to combat insects such as the species: Beauveria bassiana Metarhizium sp They also can be used against weeds (bio-herbicides) Alternaria and Colletotrichum Fungi can also used against other fungi (mycofungicides) such as species: Trichoderma Clonostachys Ampelomyces Basics in fungal biology Fungal cell biology As eukaryotes fungi contain nucleus, plasma membrane, mitochondria and complicated endomembrane system Based on the morphology fungi can be grouped into yeasts molds (filamentous fungi) Yeasts are usually unicellular and produce yeasts round pasty colonies on agar Molds are mutlicellular and form threadlike structures called hyphae Hyphae form a matlike structures called mycelium (thallus) molds Fungal cell biology Many fungal species of medical importance are dimorphic 25oC 37oC yeasts molds dimorphic (many medically important species) Fungal cell biology Fungal cytoplasm The fungal cell contains: The endoplasmic reticulum Golgi apparatus Vacuoles Vesicles Nucleus Cytoskeleton Woronin bodies: protect the hyphae from injuries, plugging the septal pores Fungal cell biology Fungal cell wall The cell wall is dynamic structure assembled at the surface of plasma membrane resisting to the turgor pressure The cell wall is composed of: glucans chitin cell wall proteins Chitin is a polymer with an important role in cell wall osmotic stability and it is absent from animal and plant cells Fungal cell biology Fungal plasma membrane The sterol molecule, ergosterol, is a distinguishing component of fungal plasma membranes It performs the same function as cholesterol in animal cells modulating fluidity and permeability ergosterol, is a good target for the antifungal drugs (Amphotericin B) Fungal growth and cell division daughter cells Bud formation in yeasts is regulated throughout the cell cycle producing one daughter at each mitotic division Mother cells The daughter cells can elongate to form sausage-like calls called pseudohyphae Fungal growth and cell division Spitzenkörper Spitzenkörper: a dense mass of vesicles controls cell wall synthesis at the hyphal tip Fungal life cycles and reproduction Haploid lifecycle: In the majority of fungi, all structures are haploid except the zygote Diploid lifecycle: the thallus has two alleles of each gene. Saccharomyces cerevisiae can exist as haploid, diploid or polyploid. Dikaryotic (heterokaryon) lifecycle: these cells have two haploid nuclei with different genetic background that do not fuse immediately (mostly common in Basidiomycota).  Fungal reproduction Asexual reproduction Fungi mostly reproduce asexually The form of fungus producing asexual spores is termed anamorph conidia sporangia chlamydospores  Fungal reproduction Sexual reproduction Some fungi also reproduces sexually The form of fungus producing sexual spores is termed teleomorph (confusing!) They produce: ascospores (Ascomycetes) basidiospores (Basiomycetes) ascospores basidiospores zygospores (Zygomycetes) Fungi usually have two mating types (genders) Either in the same body (homothallic) or In different bodies (heterothallic) zygospores Fungal reproduction Sexual reproduction An ascocarp or ascoma is the fruiting body of an ascomycete where asci with ascospores are growing apothecium cleistothecium naked asci perithecium Fungal reproduction Sexual reproduction A basidiocarp, also called basidioma, is a fruiting body, in which sexually produced spores are formed on the surface of club-shaped structures Fungal reproduction Parasexuality Recombination of genes that does not involve meiosis It can happen rarely when two haploid nuclei are fused Mitotic crossing over in these diploid nuclei can occur and generates diversity Errors in mitosis are quite common and can result to aneuploidy Fungal genome recombination Transposable elements (TE): DNA fragments move from one location to another and changes gene architecture and function Horizontal gene transfer (HGT): transfer of genes not only across fungal species but also gene acquired from bacteria and plants. Epigenetics: DNA methylation occurs in many fungi, and is a genome defense against TEs and other ’’alien’’ DNA Ø Repeat induced point mutations (RIP): is a unique process in fungi to protect their genome against TEs Diagnostics in medical mycology Early diagnosis of fungal infection is critical to effective treatment Traditional approaches to diagnosis include: direct microscopic examination of clinical samples histopathology culture serology Emerging technologies include molecular diagnostics and antigen detection in clinical samples. Innovative new technologies that use molecular and immunoassay platforms  Diagnostics in medical mycology Diagnosis of invasive fungal disease (IFD) is challenging because current diagnostic methods lack sensitivity and specificity, or take too long to yield a result to be clinically useful. Such limitations have consequences; delayed diagnosis leads to delayed treatment Diagnostics in medical mycology Molecular Diagnostic Methods Sequencing of fungal ribosomal targets is a well-known diagnostic method The regions, called the internal transcribed spacer (ITS) sequences, consist of two regions (ITS1 and ITS2) that are not part of the fungal ribosome and are spliced out after transcription Their presence confers the sequence variability that makes rDNA sequencing the most powerful nucleic acid–based diagnostic method available Diagnostics in medical mycology Questions?