Mycology Study of Fungi

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

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

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

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

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

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

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

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

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

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

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 Sporangiospores Within a sac, sporangium End of sporangiophore

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

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

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

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

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

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

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

Systemic Mycoses Dimorphic fungi Can spread throughout body 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

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

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

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

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

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

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

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

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

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

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