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Fungi
Looking Ahead
On completing this chapter, you should be able to:
o Appreciate some of the novel features of fungi that encourage scientists to place them in their
own kingdom;
o Understand the sexual and asexual reproductive cycles of fungi and compare these cycles to
those of other microbes;
o Explain how fungi benefit society in the production of various foods, the synthesis of key
industrial products, and the cycling of elements in the environment;
o Describe several important fungal diseases that affect plants and humans;
o Understand the nature of yeasts and the biochemistry of their metabolism as it relates to the
bread and fermentation industries;
o Name and describe four groups of fungi and identify key members of each group;
o Recognize the important roles assumed by fungi in lichens and in mycorrhizae.
Survival during a Bleak Era
o Fungi may have filled niche during dinosaur extinction
o Plants did not survive the extinction, either
o Fungi survived by feeding off decaying animal and plant matter
The Need for Fungi
o Ecologically important decomposers.
o The saprophytes live on dead organic matter
o Break down complex organic molecules into simple molecules that can be used by other
organisms.
Classification, Structure, and Growth of Fungi
Terms
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Yeasts
Molds
Hypha: strand of cells
Mycelium: A mass of hypha
Mycology: Study of fungi
Mycosis: Disease caused by fungi
Classification, Structure, and Growth of Fungi
Structure of fungi
o Eukaryotic
o Nuclei and other organelles
o Many fungi form spores
o No chlorophyll
o Reproduce sexually and asexually
o Cell walls contain chitin
o Septa (incomplete walls between cells)
Classification, Structure, and Growth of Fungi
Nutrition in fungi
o Almost all heterotrophic
o Digestive enzymes secreted outside cell
o Simple breakdown products absorbed by cell
o Cellulase
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Glucose stored as glycogen
Most fungi exist as saprobes
Some fungi exist as parasites
Classification, Structure, and Growth of Fungi
Nutrition in fungi
o Usually exist in acidic conditions
o Therefore fungi can grow in familiar acidic foods
o Sour cream
o Yogurt
o Citrus fruit
o Most vegetables
o Bread
o Cheese
o Favorable contamination
o Cheese (e.g., blue cheese and Penicillium requeforti)
Reproduction in fungi
Asexual reproduction
o Arthospores
o The hypha fragments and each fragment becomes a new hypha and eventuallly a new mycelium
o Chlamydospores
o Mitosis occurs resulting in two identical daughter cells. These develop into spores.
o Spores are in a sac structure called a sporangium or on the tip of a specialized Hypha called a
condiophore in which case the spores are called conidia.
o Asexual reproduction gives a large number of spores
Reproduction continued.
Sexual Reproduction
o Cell fusion and and spore formation (fig 8.5 of text)
o Cells of fungi are normally haploid (1 set of chromosomes)
o Haploid parent cells cells fuse
o Diploid progeny, called zygote
o Meiosis of zygote creates haploid spores.
o In the process genes from each parent chromosome are mixed
o Spores are environmentally resistant, like bacterial spores
o Spores germinate to form new haploid organism
o Results in fewer spores, but more genetic diversity
Classification, Structure, and Growth of Fungi: Sexual Reproduction in Fungi
Reproduction in fungi
o Asexual reproduction
o Spores
o Formed on sporangium or conidiophore
o Conidium
o Environmentally stable, like bacterial spores
o Produces extremely large number of spores
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Divisions of Fungi
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All spores are genetically identical to parent cell
Zygomycota:
zygote fungi. Make diploid spores
Asomycota:
Develop a spore sac.
Basidiomycota:
Mushrooms are the spore producing bodies of the larger fungus.
Deuteromycota :
Method of sexual reproduction has not been identified
Divisions of Fungi
Zygomycota
o Called zygomycetes
o Zygospores
o Thick-walled, environmentally resistant spores
o Develop from fusion of two sexually opposite cells
o Rhizopus stolonifer: common black bread mold
o Fermentation of rice into sake by one Rhizopus species
o Cortisone production by different Rhizopus species
Divisions of Fungi
Asomycota
o 30,000 species of ascomycetes (a.k.a., sac fungi)
o Asci
o Most are filamentous
o Some are yeasts
o Septa allow mixing of adjacent cells’ cytoplasms
o Ascocarps
o Ascospores
Divisions of Fungi
Asomycota
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Various Penicillium species
Antibiotics
Penicillin, Ampicillin, Amoxicillin, Methicillin
Blue cheese
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Various Aspergillus species
Contaminate house dust
Cause allergies, respiratory illness
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Aflatoxins
Production of food products
Citric acid, Soy sauce, Vinegar, Beano
Divisions of Fungi
Asomycota
o Claviceps purpurae
o Infects rye
o Ingestion results in ergot disease in humans
o Potential headache cure, in low doses
o Potential bioterrorism weapon
o May have contributed to the French revolution
Basidiomycota (spore form in gills at the base)
o Includes mushrooms
o Called basidiomycetes
o Basidiocarp (the fruiting body we know of as a mushroom)
o Dikaryotic stage (long stage where cells have two haploid nucleI)
o Nuclei merge to become diploid. They then undergo meiosis to form haploid Basidiospores.
o Divisions of Fungi: Life Cycle of Basidiomycota
Basidiomycota
o About 25,000 named species
o Puffballs
o Shelf fungi
o Earthstars
o Stinkhorns
o Jelly fungi
o Gill fungi (including poisonous ones)
o Rust disease
o Smut disease
o Also included many edible mushrooms including the Shitake
Deuteromycota
o About 25,000 species
o No currently identified form of sexual reproduction
o Also known as deuteromycetes or Fungi Imperfecti
o Conidia
o Many human pathogens
o Dermatophytes of athlete’s foot
o Pseudomassaria
 Chemical that mimics effects of insulin
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Beneficial and Harmful Fungi
Yeasts
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Saccharomyces
Asomycota
Single cells
Saccharomyces cerevisiae
Baking
Accumulation of CO2 during Krebs cycle makes dough rise
Enzymes break down gluten, giving spongy texture
Saccharomyces ellipsoideus
Brewing
Fermentation results in production of CO2 and ethanol
Different starting materials give rise to wines and beers
Beneficial and Harmful Fungi
Yeasts
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Tools for biotechnology
Vaccine for hep B is produced by modified yeasts
Tools for human genome project
Aided in discovering the sequence of DNA
Lichens
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Association between fungus and photosynthetic partner
Approximately 15,000 lichen species
Almost all have astomycete as the fungus
Most frequent photosynthetic partners
Trebouxia (green algae)
Trentephila (green algae)
Nostoc (cyanobacterium)
Lichens
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Grow in a diversity of environments
Arid deserts
Arctic zones
Bare soil
Tree trunks
Rocky areas
Photosynthetic partner provides sugar and carbohydrates
Fungal partner supplies protection and basic biochemical building blocks
Can survive in as little as 2% water
Very slow growth (less than 10 mm per year)
Used to estimate age of artifacts.
Mycorrhizae
o Mutualistic fungi that live amongst roots of vascular plants
o Over 5,000 species
o Plant provides photosynthetic products
o Fungi provide more nutrients than plant can absorb through roots alone
o Garden plants typically associate with zygomycetes
o May have aided plants moving from the oceans onto land.
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Fungi and human disease
Candida albicans
o Normal vaginal flora
o Held in check by other acid-producing flora
o Overuse of antibiotics, which may kill normal flora, leads to yeast infection (candidiasis)
o Can be treated
o Antifungal creams
o Eating yogurt
o Normal oral flora
o If immune depleted (e.g., AIDS), can infect mouth
o Disease is called thrush
o Treatment with oral antifungals
Cryptococcus neoformans
o Infects lungs and meninges
o In soil and pigeon droppings
Tinea diseases
o Skin infections
o Athlete’s foot
o Barber’s itch
o Jock itch
o Ringworm
Coccidioides immitis
o Respiratory disease
o American Southwest
o May proceed to meningitis
o Sometimes called Valley Fever (San Joaquin)
o Potential bioterrorism weapon
Histoplasma capsulatum
o Found in bird droppings
o Respiratory illness
Blastomyces dermititidis
o Found in bird droppings
o Respiratory illness
Final thoughts
o Please read your text:
o Review the video’s on the Fungi as well as other links posted to the right in the softchalk
lesson.
o Learn the key terms located on page 168 of your text.
o For additional quizzes and exercises you should go to the textbook site.