Lecture 22 focuses on Fungi 1, following Lecture 21 on Angiosperms. The subsequent lecture, 23, will be Fungi 2.
Lab 6 involves studying lichens, life cycles, major fungal groups, their form, and heterotrophy.
Learning Goals
Explain key innovations of fungi.
Describe key features of major groups of fungi.
Compare and contrast main features of growth and cellular structures seen in fungi.
Understand and be able to give examples of ways in which humans make use of fungi.
Explain key aspects of life cycles of fungal groups, especially dikarya and their unique patterns.
Explain the general concepts for each of the “top 9 things to know about fungi.”
Introduction to Fungi
Fungi are incredibly diverse.
Fungi have significant importance in various aspects.
Fungi by the Numbers
Approximately 150,000 described species.
Estimated to be more than 5 million species.
8,000 species are plant pathogens.
300 species are human pathogens.
> 20 Billion in agricultural damage in US per year.
> 10 Billion in human health impacts in US / year.
The largest fungus covers > 4 square miles.
Fungal Features
Mostly chemo-heterotrophic.
Mostly non-motile.
Exist in unicellular, colonial, and multicellular forms.
Incredibly widespread and ecologically important.
Many are symbiotic.
Most reproduce via spores.
Possess diverse and novel life cycles.
Fungal Pathogen Spread With Climate Change
Changing climate is expected to shift suitable areas for Aspergillus flavus.
Suitable area shifts north as climate warms.
Some areas no longer suitable.
TNTESKAF Part 1
1. Fungi are Opisthokonts
Fungi are in the same eukaryotic group as animals (Opisthokonts).
Fungi and Animals share some features not seen in many other eukaryotes.
Some consequences of this:
Fungi are good model organisms for studying some aspects of animal biology
Some drugs that target fungi have unwanted side effects on animals
Fungal infections have massive impacts on humans, animals, plants, and other organisms.
Many antifungal drugs target ergosterol, found in fungal membranes.
Unfortunately many are toxic to humans and thus only used as last resort
Toxicity in animals is due to these drugs affecting cholesterol which is chemically very similar to ergosterol
Similarity is due to common ancestry of sterol use in fungi and animals
Sterol use in membranes evolved in a common ancestor of fungi and animals
Fungi are good “model organisms” for studies of eukaryotes generally but also for animals
2. Fungi are divided into six major groups
Microsporidia
Unicellular
Intracellular parasites of animals
Some cause human diseases (e.g., microsporidiosis)
Chytrids
Swimming spores and gametes aid in dispersal
Many are pathogens
Implicated in global amphibian declines
Zygomycota
Rhizopus oligosporus used to make tempeh
Rhizopus stolonifer: black bread mold. May be most common fungus in the world
Rhizopus stolonifer: causes grape rot
Zygomycosis: Serious human disease
Novel life cycles
Many food “contaminants”
Many are pathogens
Glomeromycota (Arbuscular mycorrhizae)
All glomeromycota are multicellular mutualistic symbionts of plants forming mycorrhizae (that look like small trees or arbuscles) with plants at the roots
Dikarya
Dikaryotic stage of life cycle
Plasmogamy precedes karyogamy
Basidiomycota (club fungi)
Many unicellular
Many multicellular including some “mushrooms”
Ascomycota (sac fungi)
Many unicellular
Many multicellular including some “mushrooms”
3. Chitin in cell walls is a key fungal feature
Traits that evolved could be good targets for antifungal drugs that would be less likely to be toxic to humans & other animals
Chitin: long polymer of N- acetylglucosamine (an amino- sugar similar to glucose)
Found in the cell walls of fungi
Functions in fungal cell walls in similar ways to peptidoglycan of bacteria - protects cells, provides rigid structure
Also found in other taxa (e.g. insects) but the way it is used in the cell wall is unique to fungi
Good target for antifungal drugs
Fungi and their products are common in our diet
Mushrooms
Molds in cheese
Chitin digested in humans w/ aid of immune system
The use of chitin in cell walls is a synapomorphy of fungi
Chitin is used to provide rigid structural support much like peptidoglycan is used in bacteria
Chitin is a good target for anti-fungal drugs because it is in all fungi and is functionally critical
Even when found in other taxa (e.g., arthropods) it is used in different ways
Digestion of chitin is important for consumption of fungi by various organisms (e.g., humans)
4. Multicellular fungi are organized using hyphae
Many fungi are single celled some or all of the time
Many fungi are multicellular
Hyphae are chains of cells, many cells long and one cell thick.
Cell walls (when present) have chitin.
Forage via growth of hyphae
Single cell width of hyphae means most cells in contact with environment
This allows high surface area to volume ratio which aids in absorption but makes susceptible to desiccation.
Collections of hyphae = mycelia
Mycelia of single fungi can get very very very big
Hyphae-like structures seen in many other taxa
5. Fungi digest externally
Absorptive heterotrophy
Three main components to “trophy”
Energy source
Light: Photo
Chemical: Chemo
Electron source (reducing equivalent)
Inorganic: Litho
Organic: Organo
Carbon source
Carbon from inorganics: Auto
Carbon from organics: Hetero
Absorptive heterotrophy:
Enzymes secreted
These break down large compounds (e.g., carbohydrates, proteins, fats, etc)
Breakdown products imported into cells
Targets:
Living organisms (e.g., in fungal pathogens and mutualists)
Dead and decaying organic matter (in saprobic fungi)
Compounds provided by other organisms (e.g., sugars from mutualistic partners, humans for fermentation, industrial purposes).
Globally, decomposition of organic matter and recycling of many nutrients driven largely by fungi
Fungi will grow on items, secrete enzymes, and degrade and alter sugars, proteins, etc - producing useful products (e.g., alcohol, CO2) and altering flavors in diverse ways.
Many consequences of living by absorptive heterotrophy
Production of chemicals to inhibit other organisms to prevent “stealing” of breakdown products
Most fungi are non motile so to get access to new food need to:
Explore/forage via growth of hyphae
Disperse spores to new locations
Attract / trap organisms to consume
Symbioses with other organisms
Use animals to disperse
High surface area helps get access to external sources of nutrients
High surface area leads to being prone to desiccation
Fungi possess array of compounds to inhibit growth of organisms
Many of these used b/c “absorptive heterotrophy” leads to competition to take up degraded compounds
Many antibiotics isolated from fungi
Including some that are the “last line” against resistant microbes
Many toxic chemicals from mushrooms, some of which have other uses