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Mycology. Study of Fungi. 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. Significance. Beneficial

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mycology

Mycology

Study of Fungi

characteristics
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
significance
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
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
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
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
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
Yeasts
  • Unicellular fungi
  • Budding yeasts-uneven cell division
  • Protuberance forms -bud
  • Nucleus divides & one goes into bud
  • Cell wall material laid down
p seudohypha
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
dimorphic fungi
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
Reproduction
  • Filamentous fungi
    • Asexually by fragmentation of hyphae
    • Asexual and sexual reproduction by spores
  • Yeasts
    • Asexually by budding or fission
    • Sexual reproduction by spores
asexual 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
      • Several types
    • Sporangiospores
      • Within a sac, sporangium
      • End of sporangiophore
sexual spores
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
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
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
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
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
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
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
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
histoplasmosis
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
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
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
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
opportunistic pathogens
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
disease26
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
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
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
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
lichens30
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