Lecture 19: Fungi Flashcards by Cagn Walker

Fungal usages for humans

•Food
-Bread, some cheeses, alcoholic beverages
•Important drugs
-Antibiotics—Penicillin, cephalosporin
-Cyclosporin—an anti-rejection drug

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Dangers of fungi

-Some are parasitic in animals
-Some cause important diseases in plants

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Fungi beneficial roles

•Decompose dead organisms-recycle nutrients
•90% of plants form mycorrhizae
-Fungal associations with roots helps absorb water and minerals

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Fungi 5 phyla

•Chytrids
•Zygomycetes
•Glomeromycetes
•Ascomycetes
•Basidiomycetes

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Penicillin discovery

Sir Alexander Fleming in 1929

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Fungi types

•Yeast
-Small round single cells
•Molds
-long branched filaments called hyphae
•Some fungi are dimorphic
-can grow as both yeast-like cells and mold-like cells

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Yeasts

•unicellular fungi
•Many are Ascomycetes
•Most reproduce by budding
•include the common model yeast: Saccharomyces cerevisiae (aka Brewer’s yeast or baker’s yeast

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Lee Hartwell

Won Nobel Prize in 2001 for studies using budding yeast (Saccharomyces cerevisiae

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Paul Nurse

Nobel prize in 2001
-Cell cycle studies in S. Pombe (co-awarded with Lee Hartwell)

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Fungal division types

•Division by budding and fission
•Dendritic colony morphology
•Repeated, simultaneous multi-budding
•Meristematic division, filamentation, and cellularization

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Fungi quality

•Fungi are often heterotrophs
-Feed on preformed organic material
•Fungi digest THEN ingest
•Fungi produce hydrolysis enzymes that are secreted and break-up organic material
•Digested food absorbed
•Many fungi are saprobes
-Get nutrients from dead organisms

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Saprobes

Use non-living material
Important scavengers

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Parasites

Use organic material from living hosts, harming them in some way

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Mutualists/Symbionts

Fungi that live in association with the host without harming it (and often helping it).

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Molds

•Molds are filamentous fungi
•Cells may contain more than one nucleus, sometimes 100:
-A single filament is known as a hypha: a nucleated tube containing cytoplasm
•Some grow below the surface
-Largest organism on Earth may be Armillaria -Spreads over 1000s of acres and several feet deep.

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Common molds

-Rhizopus
-Aspergillus

Spores

Aerial hypha form conidia: asexual spores

Mushrooms

•Basidiomycetes
-Filamentous fungi that form fruiting bodies
•Sexual spores

Sexual spores

(Basidiospores) on the underside on the cap of the mushroom. Spores dispersed by wind.

Mycorrhizae

•’Fungal-root’
•Rootz of most terrestrial plants are mycorrhizal
•Mycorrhizal fungi get their carbon from root secretions and inorganic minerals from the soil
•Mycorrhizal plants get more nutrients from the soil due to greater surface area from fungal filamentous cells

Mycorrhizae phyla

•Zyomycetes
•Glomeromycetes
•Ascomycetes
•Basidiomycetes

Mycorrhizal interaction

-Ectomycorrhiza and endomycorrhiza
•Fungus provides inorganic materials for plant (N and Pi)
•Plant provides organic materials (C based) for fungus
Mutualistic interaction

Truffles

Truffles are ectomycorrhizal fungi and are therefore usually found in close association with the roots of trees

Plant fungal pathogens

•Dutch elm disease
•Corn smut
•Rice blast

Magnaporthe oryzae

Causes rice blast, the most serious disease of cultivated rice

Chytrids

Infect frogs, causes loss in amphibian biodiversity Accelerated spread due to climate change

P. destructans

An ascomycetous fungus associated with bat “White-Nose syndrome” (WNS) -An emerging disease of hibernating bats

Human pathogenic fungi

•Most serious ‘mycoses’ are not contagious -do not spread by person to person contact -Result from exposure to environmental sources •Dermatophytes are contagious -Live in dead layers in the skin -ex. Ringworm •Only 4 know fungi are true human pathogens (most are opportunistic) •Dimorphic depending on temperature

Candidiasis

•Candida is part of normal microbial flora on skin and mucous membranes -Normal part of GI tract in most people -A pathobiont—lives in association with outer organisms but don’t derive their nutrition from them •Causes both mucosal infections (oral thrush, yeast infections) and bloodstream infections (typically in immuno-compromised individuals, target macrophages)

Biofilms and candida infections

•Yeast cells attach to the surface •Grow up several layers of cells • Switch to form hyphae and extracellular matrix formed •Dispersal to new sites

Why are biofilms drug resistant?

•Physical barriers to the drug •Non-dividing cells/persister cells that are more resistant to the drug • Cells in biofilms can activate responses that decrease drug efficiency (E.g., unregulate effluent drug transporters)

Candida albicans produces a toxin

Ece1 is a secreted peptide (“candidalysin”) that generates pores in host cells Candidalysin allows candida to colonize the gut

Did fungi end the reign of the dinosaurs?

Mammals are more resistant to fungal infections due to higher body temperature, this out-survived the dinosaurs when fungi began to flourish