IV. Fungi KNOW RED STUFF

A. Overview

1. General Characteristics

- multicellular eukaryotes

- heterotrophic

- absorptive nutrition:

excrete enzymes into environment and absorb the product of that digestion. They digest dead matter (decomposers) or live matter (pathogens), or may be symbiotes.

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2. Classification

- Chytridiomycota

- Zygomycota

- Ascomycota

- Basidiomycota

Single celled members of these groups are all called “yeasts”. They are distinguished from protists based on a chitinous cell wall and absorptive (rather than phagocytic) nutrition.

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3. General Biology

- The organism is composed of threadlike “hyphae”

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3. General Biology- The organism is composed of threadlike “hyphae”- The hypha can be coenocytic (without divisions) or septate (with incomplete cell walls between)

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3. General Biology- The organism is composed of threadlike “hyphae”- The hypha can be coenocytic (without divisions) or septate (with incomplete cell walls between)- These have a huge surface area/volume ratio for absorption.- The largest organisms known… 37 acres.

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4. Ecological Roles

- decomposers: Fungi decompose lignin and cellulose, which most free-living bacteria can’t digest.

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4. Ecological Roles

- decomposers: Fungi decompose lignin and cellulose, which most free-living bacteria can’t digest.

* antibiotics

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4. Ecological Roles

- decomposers: Fungi decompose liginin and cellulose, which most free-living bacteria can’t digest.

* antibiotics

- mycorrhizae: fungal symbiotes of certain plants. The fungus increases the absorbance area of roots dramatically, and passes water and nutrients to the plant. The plant feeds the fungus with glucose.

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4. Ecological Roles

- decomposers: Fungi decompose liginin and cellulose, which most free-living bacteria can’t digest.

* antibiotics

- mycorrhizae: fungal symbiotes of certain plants. The fungus increases the absorbance area of roots dramatically, and passes water and nutrients to the plant. The plant feeds the fungus with glucose.

- lichens – symbiote with alga

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4. Ecological Roles

- decomposers: Fungi decompose liginin and cellulose, which most free-living bacteria can’t digest.

* antibiotics

- mycorrhizae: fungal symbiotes of certain plants. The fungus increases the absorbance area of roots dramatically, and passes water and nutrients to the plant. The plant feeds the fungus with glucose.

- lichens – symbiote with alga

- pathogens – Athlete’s foot, ringworm, yeast infections

- parasites – entomophagous fungi

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B. Zygomycetes

- coenocytic hypha

- asexual reproduction haploid hypha produces sporangia and releases spores.

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B. Zygomycetes

- sexual reproduction – hypha touch, and produce gametangia. Gametes produced inside – fusion into dikaryotic cells (2 nuclei). Each dikaryon then becomes diploid (fusion of nuclei and undergoes meiosis. Spores are released.

- many are imporant mycorrhyzal symbionts.

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C. Ascomycetes

- septate hypha

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C. Ascomycetes

- septate hypha

- characterized by production of spore-bearing “asci”

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C. Ascomycetes

- septate hypha

- characterized by production of spore-bearing “asci”

- baker’s yeast

(levening and fermentation)

- molds – pathogens of plants such as Aspergillus, Penicillium, Neurospora, Chestnut Blight, Dutch Elm disease, etc.

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C. Ascomycetes

- life cycle

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D. Basidiomycetes

- bear puffballs or mushrooms as fruiting bodies

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D. Basidiomycetes

- bear puffballs or mushrooms as fruiting bodies

- haploid hyphae fuse in dikaryotic hyphae.

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D. Basidiomycetes

- bear puffballs or mushrooms as fruiting bodies

- haploid hyphae fuse in dikaryotic hyphae.

- these dikaryotic hyphae form the fruiting structure.

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D. Basidiomycetes

- bear puffballs or mushrooms as fruiting bodies

- haploid hyphae fuse in dikaryotic hyphae.

- these dikaryotic hyphae form the fruiting structure.

- at the tip of each hyphae, the basidium forms, in which meiosis occurs to produce new haploid spores.

- life cycle

Characteristics of Fungal Hyphae:Septate versus Coenocytic

Mycelium: Large, Visible Mass of Hyphae

IMPORTANT DIVISIONS OF FUNGI

1. Deuteromycota Not known to produce sexual spores.

Reproduce asexually.

Catch-all category for unclassified fungi:

– Pneumocystis carinii: Causes pneumonia in AIDS

patients. Leading cause of death in AIDS patients.

Originally classified as a protozoan.

– Candida albicans: Causes yeast infections of vagina in

women. Opportunistic infections of mucous

membranes in AIDS patients.

Opportunistic Infection by Candida albicans in an AIDS Patient

Source: Atlas of Clinical Oral Pathology, 1999

Life Cycle of Eupenicillium (Ascomycete)Reproduces Asexually and Sexually

Severe nail infection with Trichophyton rubrum ina 37-year-old male AIDS patient.Source: Intern. J. Dermatol. 31(1992): 453.

Disseminated Histoplasma capsulatum, skin infection.Source: Microbiology Perspectives, 1999.

FUNGAL DISEASES

Mycosis: Any fungal disease. Tend to be chronic because fungi grow slowly.

Mycoses are classified into the following categories:

I. Systemic mycoses: Fungal infections deep within the body. Can affect a

number if tissues and organs.

Usually caused by fungi that live in the soil and are inhaled. Not contagious.

Examples:

– Histoplasmosis (Histoplasma capsulatum): Initial infection in lungs. Later

spreads through blood to most organs.

– Coccidiomycosis (Coccidioides immites): Resembles tuberculosis.

Systemic Mycosis: Histoplasmosis

Disseminated Histoplasma capsulatum, lung infection.Source: Microbiology Perspectives, 1999.

FUNGAL DISEASES (Continued)

II. Cutaneous mycoses: Fungal infections of the skin, hair, and nails.

Secrete keratinase, an enzyme that degrades keratin.

Infection is transmitted by direct contact or contact with infected

hair (hair salon) or cells (nail files, shower floors).

Examples:

– Ringworm (Tinea capitis and T. corporis)

– Athlete’s foot (Tinea pedis)

– Jock itch (Tinea cruris)

Cutaneous Mycosis

Ringworm skin infection: Tinea corporisSource: Microbiology Perspectives, 1999

Cutaneous Mycosis

Candida albicans infection of the nails.Source: Microbiology Perspectives, 1999.

FUNGAL DISEASES (Continued)

III. Subcutaneous mycoses: Fungal infections beneath the skin.

Caused by saprophytic fungi that live in soil or on vegetation.

Infection occurs by implantation of spores or mycelial fragments

into a skin wound.

Can spread to lymph vessels.

IV. Superficial mycoses: Infections of hair shafts and superficial

epidermal cells. Prevalent in tropical climates.

FUNGAL DISEASES (Continued)

Opportunistic mycoses: Caused by organisms that are generally

harmless unless individual has weakened defenses:

– AIDS and cancer patients

– Individuals treated with broad spectrum antibiotics

– Very old or very young individuals (newborns).

Examples:

– Aspergillosis: Inhalation of Aspergillus spores.

– Yeast Infections or Candidiasis: Caused mainly by Candida

albicans. Part of normal mouth, esophagus, and vaginal flora.

ECONOMIC IMPORTANCE OF FUNGI 25-50% of harvested fruits and vegetables are damaged by fungi.

Fungal infections of plants are commonly called rots, rusts, blights,

wilts, and smuts.

– Phytophthora infestans: Caused great potato famine in mid-

1800s. Over 1 million people died from starvation in Ireland.

Many immigrated to the U.S.

Beneficial fungi:

– Candida oleophila: Prevents fungal growth on harvested fruits.

– Saccharomyces cerevisiae: Used to make bread and wine.

– Genetically engineered yeast strains are used to make proteins

(Hepatitis B vaccine).

– Taxomyces: Produces anticancer drug taxol.

– Trichoderma: Produces cellulase. Used to make fruit juice.