Mycology Introduction Notes

Lecture 29: Mycology Introduction

Biology of Infection and Immunity
Dr. Stephanie Zukowski
March 31st, 2025

Learning Outcomes

By the end of this lecture, students will:

  • Demonstrate an understanding of mycology as a field of study.

  • Describe general classifications and characteristics of filamentous fungi.

  • Describe general classifications and characteristics of yeast.

  • Differentiate general life cycles of filamentous fungi and yeast.

  • Explore the impact and potential benefits of fungi on humans and the environment.

Fungi Are Closer to Humans than Plants

Fungi share more biological similarities with humans than plants, highlighting their significance in life sciences.

Cell Structure

  • Plant Cells:

    • Cell wall made of cellulose.

    • Generally possess one nucleus per cell.

    • Autotrophic (make their own food).

    • Membranes contain phytosterols.

    • Store food as starch in granules.

      • branched or unbranched

  • Fungal Cells:

    • Cell wall made of chitin.

    • May be uninucleated or multinucleated.

    • Heterotrophic (obtain food from other sources).

    • Membranes contain ergosterol.

    • Store food as glycogen in granules.

Classification of Fungi

  • Spore Formation

  • Fungal Genomics

  • Modes of Nutrition:

    • Saprophytic: Obtain nutrition from dead organic substances.

    • Parasitic: Obtain nutrition from living hosts (plants/animals).

    • Symbiotic: Engage in interdependent relationships for mutual benefit.

      • Examples:

        • Lichens ( algae and a fungus )

        • Mycorrhiza

      • Genera: Puccinia, Aspergillus, Penicillium.

Fungal Morphology

Filamentous Fungi

  • Macrofungi ( fruiting body )

  • Microfungi ( mold )

Yeast

  • microfungi molds

Fungal Reproduction

  1. Asexual

    • Most common, referred to as anamorphs.

    • Involves spores produced through mitosis.

  2. Sexual

    • Referred to as teleomorphs.

    • Involves fusion of two nuclei followed by meiosis.

  3. Parasexual

    • Involves genetic recombination without specific structures.

Filamentous Fungi Life Cycle

  1. The Mushroom (Fruitbody)
    This is the part you see above the ground – like the cap and stem of a mushroom. It’s kind of like the flower of a plant.

  2. Spores Fall Out
    The mushroom releases tiny seeds called spores into the air. These are super small – you can't see them without a microscope!

  3. Spores Land on the Ground
    If the spores land in a good spot with moisture (water) and food (like dead leaves or wood), they start to grow.

  4. Hyphae Start Growing
    The spores grow into thin, thread-like structures underground called hyphae. Think of hyphae like roots that spread out and help the mushroom eat.

  5. Hyphae from Different Spores Meet
    Sometimes hyphae from different spores bump into each other and join together – kind of like mushroom teamwork!

  6. More Hyphae Grow and Feed
    These connected hyphae keep spreading out under the ground and suck up nutrients from the soil to help the mushroom grow.

  7. A New Mushroom Pops Up
    When the hyphae have enough energy and the conditions are right, a baby mushroom starts to grow above the ground.

  8. The Cycle Starts Over
    That mushroom grows up, releases more spores, and the process begins again!

Vegetative Growth

  • Fungi grow as filaments (hyphae) extending at their tips, exhibiting apical growth.

  • Fungal hyphae branch repeatedly behind their tips, giving rise to a network termed a mycelium

  • Hyphae can be:

    • Septate: Divided by septa.

    • Coenocytic: Lacking septa, multinucleated cells.

Aspergillus nidulans life cycle

1. Asexual Cycle (Cloning - no mating involved)

  • Conidium (a tiny spore) is made by a structure called a conidiophore.

  • These spores spread and land somewhere with food and moisture.

  • They grow into new fungal cells (hyphae) that are genetically identical to the parent—like a copy-paste.

  • This is the quickest and most common way this fungus spreads.


2. Sexual Cycle (Involves mating)

  • Two hyphae from different mating types (like male and female types) come together.

  • Their nuclei (DNA centers) combine and form a special round structure called a cleistothecium.

  • Inside it, cells called asci form and produce ascospores.

  • These ascospores are released and grow into new fungi with mixed DNA from both parents.

  • This helps increase genetic diversity, like how siblings can look different.


3. Parasexual Cycle (A mix, without a full sexual process)

  • Two different hyphae fuse together (hyphal fusion).

  • This forms a heterokaryon, which means the cells contain different types of nuclei.

  • The nuclei then fuse to form a diploid (2 sets of chromosomes) cell.

  • Over time, the fungus randomly loses chromosomes, leading to new genetic combinations—but without going through full sexual reproduction.

  • It's like a weird in-between method that still gives variation.


Yeast

  • Approximately 1% of fungi are single-celled yeasts (e.g., Saccharomyces cerevisiae).

  • Some yeasts can switch between yeast and hyphal forms based on environmental conditions (pseudohyphae).

  • Reproductive modes include fission and budding.

Yeast Life Cycle Examples

Saccharomyces Cerevisiae ( Bakers yeast ) :


  • Asexual Reproduction (Cloning through Budding):

    • Yeast cells (either a or α types) make baby yeast cells by budding — a small part of the cell grows out and becomes a new one.

    • No partner is needed. It’s a fast way to multiply!


  • Sexual Reproduction (Happens when there’s not enough food):

    • a and α cells turn into “schmoo cells” — these are special shapes they take when they're ready to mate.

    • The two schmoo cells fuse together to form a zygote.

    • This zygote can bud like normal, but if nutrients are very limited, it undergoes meiosis (a special kind of cell division) and forms an ascus containing 4 spores (called ascospores).

    • These spores can each grow into a new yeast cell when the environment improves.


    Schizo-Saccharomyces Pombe: Studied for cell division and genetics.


  • Mitotic Cell Cycles (Normal Growth):

    • In good conditions, it stays in the haploid (single set of genes) or diploid (two sets of genes) state and keeps dividing normally.


  • Sexual Reproduction (Triggered by starvation):

    • When food is low, haploid cells of opposite mating types (like “plus” and “minus”) come together and fuse.

    • This forms a zygote.

    • The zygote undergoes meiosis to form an ascus with 4 ascospores inside.

    • These spores can stay dormant until conditions improve, then each becomes a new haploid cell.

Importance of Sporulation

  • How to survive on planet earth …:

    • Reproduction

    • dissemination. ( can carry far in the wind )

    • Allows movement to new food sources. ( if something happens to enviorment can move )

    • Helps survive adverse conditions.

    • Introduces genetic diversity.

    • Source of inocula for infection

Benefits of Fungi

  • Nutrient Cycling

  • Carbon Cycling and Climate Regulation

  • Nutrition and Food Security

  • Human Health

  • Environmental Protection

  • Sustainable Materials

Fungi in Food

  • Used for Food and Medicine:

    • Mushrooms for food, medicinal use, rituals or as a means to start a fire

    • Almost 100 species have cultivation systems, mostly saprophytes.

Yeasts in Food Production

  1. Baking

    • Saccharomyces cerevisiae produces CO2 during fermentation by feeding on sugars present in bread dough.

    • Other ingredients affect fermentation speed

      • sugar and eggs speed it up

      • fats and salt slow it down

    • Ethanol is evaporated when the bread bakes

  2. Alcoholic Beverages

    • several different yeast are used for brewing beer

    • ferment sugars present in malted barley to produce alcohol

    • Saccharomyces cerevisiae is used to make ale-type beers and is know as top fermenter

    • Bottom-fermenting yeasts, such as Saccharomyces pastorianus, are more commonly used to make lagers

    • The alcohol in wine is formed by the fermentation of the sugars in grape juice often by Saccharomyces cerevisiae

  3. Cheese Production

    • Filamentous fungi important in the manufacture and ripening of :

      • Blue-veined cheeses (e.g., Roquefort, Gorgonzola, Stilton, etc.)

      • Soft-ripened cheeses (e.g., Brie, Camembert, Humboldt Fog, etc.)

  4. Mycoprotein


    • In the 1960s, scientists predicted a future shortage of protein-rich foods.

    • Efforts began to develop protein sources from microbial biomass.

    • This led to the creation of Quorn mycoprotein, a new food product.

    • Quorn is made from the filamentous fungus Fusarium venenatum.

    • It is produced commercially using chemostat cultures of fungal mycelium.

    • Quorn offers a sustainable, protein-rich alternative to traditional meat sources.

Safety Considerations

  • About 3% of known mushroom species are toxic to humans.