Mycology

1. Mycology Study of Fungi

2. Characteristics • Diverse group of chemoheterotrophs • > 90,000 known species • Saprophytes • Digest dead organic matter • Parasites • Obtain nutrients from tissues of organisms • Molds & mushrooms are multicellular • Yeasts are unicellular

3. Significance • Beneficial • Decompose dead organisms • Recycle nutrients • Mycorrhizae • Association with roots of vascular plants-truffles & oak • Assist in absorption of water & minerals • Control of pests -Gypsy moth • Food & antibiotics

4. Parasitic Fungi • Fungal diseases of plants, animals, humans, & bacteria • Irish & potatoes • Dutch elm disease • Death of chestnut trees • Crop damage-wilts, mildews • Spoilage of food- bread, oranges, jams • Athlete’s foot, aspergillosis

5. Nutrition • All are chemoheterotrophs • Absorption of nutrients: powerful exoenzymes • Grow at lower pH-5 than bacteria • Grow in high salt and sugar • Metabolize complex CH2O like lignin in wood-wood rot

6. Structure of Fungi • Vegetative structures involved in catabolism and growth • Thallus- in molds and fleshy fungi • Tubular filaments of cells-hyphae • Septate hyphae - cross walls that divide them into unicellullar units • Pores to allow cytoplasm & nuclei to pass • Coenocytic hyphae- no septa, continuous cells with many nuclei

7. Growth • Elongate at tips of hyphae • Mycelium- filamentous mass of hyphae visible to eye • Aerial hypha or fruiting body- portion concerned with reproduction • Some mycelium underground • Asexual & sexual spores

8. Yeasts • Unicellular fungi • Budding yeasts-uneven cell division • Protuberance forms -bud • Nucleus divides & one goes into bud • Cell wall material laid down

9. Pseudohypha • Elongated chain of cells • Candida albicans -buds fail to detach • Allows yeast to invade deeper tissues • Fission yeast • Divide evenly like bacteria • Visible growth on medium-colony

10. Dimorphic Fungi • Two forms of growth • Grow either as a mold or as a yeast • Dimorphism in pathogenic fungi is temperature dependent • at 37 C yeast like growth • at 25 C it is mold like • Nonpathogenic: CO2 conc • Mucor: on surface yeast, in agar mold

11. Reproduction • Filamentous fungi • Asexually by fragmentation of hyphae • Asexual and sexual reproduction by spores • Yeasts • Asexually by budding or fission • Sexual reproduction by spores

12. Asexual Spores • Produced by aerial hyphae: adapted for dispersal • Progeny genetically identical to parent • Several types • Conidiospores- not enclosed in a sac • produced in a chain at end of a conidiophore • Several types • Sporangiospores • Within a sac, sporangium • End of sporangiophore

13. Sexual Spores • Three phases of development • Plasmogamy-haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-) • Karyogamy- the 2 nuclei fuse to form a diploid nucleus • Meiosis-diploid nucleus gives rise to haploid nuclei • Sexual spores, some + , some -,some recombinants • Sexual spores used to classify fungi into divisions

14. Classification: Phylum • Zygomycota -saprophytic molds, coenocytic hyphae • Rhizopus - black bread mold • asexual spores are sporangiospores • sexual spores are zygospores -large spore enclosed in a thick wall - fusion of nuclei of 2 cells

15. Ascomycota • Sac fungi includes molds with septate hyphae and some yeasts • Talaromyces • asexual spores are conidiospores • Sexual spores-ascospores • 8 produced in sac –ascus • Ascus occurs in fruiting body-ascocarp

16. Basidiomycota • Club fungi, mushrooms, toadstools • Septate hyphae • Sexual spores- basidiospores produced externally on base pedestal-basidium • 4 per basidium • Some produce asexual conidiospores or fragmentation

17. Sexual Reproduction • Telomorphs-produce both sexual and asexual spores • Anamorphs- lost ability to reproduce sexually-Penicillium • belonged to Deuteromycota • now classified as anamorphs of other phyla: rRNA & Woese • most are ascomycetes

18. Fungal Diseases • Mycosis- fungal infection • < 100 cause human disease • Not highly contagious • Humans acquire from nature • Groups based on degree on tissue involvement and mode of entry • Cutaneous mycoses-dermatophytes • Epidermis, hair & nails • Contagious-direct or indirect contact • Secrete keratinase that degrades keratin

19. Cutaneous Mycoses • Tinea( worm) capitis –blisters with scaly ring • Ringworm of the scalp • Spreads circularly forming bald spots • Spread by contact with fomites , cats and dogs • Tinea cruris- ringworm of groin • Tinea pedis - athlete's foot • Live for weeks on shower floor or mat • 1992 outbreak among wrestlers • Diagnosis-scrapings; TX–antifungal creams

20. Systemic Mycoses • Dimorphic fungi • Yeast form is invasive • Can spread throughout body • Usually caused by fungi in soil • Inhalation of spores • Begins in lungs and spread to rest of body • Not contagious person to person

21. Histoplasmosis • Histoplasma capsulatum-dimorphic fungi • Filamentous in soil & medium • Yeast like in tissues • Ascomycetes - conidia • Exposure by inhalation of conidia • Found along Ohio River Valley • Moist soil, rich in N: droppings of birds and bats • 5% develop clinical disease • Resembles TB • Skin testing-80% in area infected

22. Diagnosis/Treatment • Grown in medium that selects for fungal growth • Grow at 25 C and 37 C • KOH preparations of skin biopsies • Dissolves keratin in skin scrapings or biopsies • Leaves only fungal cells • Therapy- amphotericin B or ketoconazole • Toxic to humans

23. Coccidiomycosis ( Valley Fever) • Coccidioides immitis-dimorphic fungi • Asexual spores (conidia) in dry alkaline soil of American SW and S America • Wind carries spores to transmit infection • Driving thru endemic area can cause disease -100,000 infections each year • Spore lodges in lung

24. Disease • Influenza like disease • High fever, cough, body aches, chest pain • Most are asymptomatic • Few progress to disseminated infection • Skin test to detect prior infection • Amphotericin B

25. Opportunistic Pathogens • Lack proteins that aid in colonization or invasion • Do not cause disease in healthy persons • Infect susceptible individuals • Aspergillosis-occurs in people with lung diseases or cancer • Inhalation of conidia of Aspergillus turn into mycelium in lungs • Organism is widespread in soil, compost piles, wood, carpets, any dust

26. Disease • Hypersensitivity –can be chronic & lead to lung damage • Noninvasive-masses of hyphae in lungs • Invasive pulmonary –pneumonia & necrosis of lung –reportable disease • Construction projects in hospitals • Protect immunosuppressed patients • Erect barriers, negative pressure

27. Candidiasis • Candida albicans part of normal flora • Anamorph • Suppressed by bacteria in mucous membranes • If pH changes or on antibiotics, allows yeast to grow and cause infection • Oral thrush or vaginitis-topical creams • AIDS pts often spreads and becomes systemic • May result in death- treat with antifungal

28. Virulence Factors • Exoenzymes attack cells & progressively digest & invade nearby cells • Capsule: some yeasts • Mycotoxins produced by mushrooms • Hallucinogenic • Damage liver • Carcinogens: aflatoxins in grain and peanuts

29. Lichens • Classified as fungi, most are ascomycetes • Combination of green alga or cyanobacteria and fungus • Mutualism- each partner benefits from relationship • Fungus obtains nutrients, water and protects partner from desiccation • Partner provides products from photosynthesis-oxygen and sugars

30. Lichens • Lichens secrete acids that break down rock • First life to colonize exposed rock • Lichens used as dyes-litmus • Food source for animals • Sensitive to pollution-SO2 • 3 morphological types