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
– 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
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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
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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
– 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
– 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
• Several types
– 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
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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
– Yeast form is invasive
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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
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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
– High fever, cough, body aches, chest pain
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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
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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