(Section D: Other Infectious Agents) Lecture 29 Flashcards
Are fungi more related to plants or humans?
Humans
Plant cell vs. Fungal cell
* Cell wall
- Plants: Cellulose
- Fungi: Chitin
Plant cell vs. Fungal cell
* Nucleus
- Plants: Generally possess 1 nucleus per cell
- Fungi: May be uninucleated or multinucleated
Plant cell vs. Fungal cell
* Autotroph/Heterotroph
- Plants: Autotrophs
- Fungi: Heterotrophs
Plant cell vs. Fungal cell
* Membrane composition
- Plants: Contains phytosterols
- Fungi: Contains ergosterol
Plant cell vs. Fungal cell
* Food storage
- Plants: Store food as starch in granules
- Fungi: Store food as glycogen in granules
Cellulose vs. Chitin
Cellulose
* β(1-4) linked D-glucose
Chitin
* β(1-4) linked N-acetylglucosamine
How are fungi classified?
- Spore formation
- Fungal genomics
- Modes of nutrition
Fungal modes of nutrition
- Saprophytic
- Parasitic
- Symbiotic
Saprophytic fungi
- Obtain nutrition by feeding on dead organic substances
Parasitic fungi
- Obtain nutrition by living on other living organisms and absorbing their nutrients
- Plants, animals can be hosts
Symbiotic fungi
- Have interdependent relationship with other species in which both are mutually benefited
What are forms of symbiotic fungi?
- Lichens: Fungi and Algae
- Mycorrhiza: Fungi and Plants
Fungal morphology
- Filamentous (macrofungi and microfungi)
- Yeast (microfungi, “molds”)
Forms of Fungal Reproduction
- Asexual
- Sexual
- Parasexual
Fungal Asexual Reproduction
- Most common
- Known as anamorphs
- Asexual propagules are known as spores, produced following mitosis
Fungal Sexual Reproduction
- Known as teleomorphs
- Sexual propagules formed by fusion of two nuclei that then generally undergo meiosis
Fungal Parasexual Reproduction
Genetic recombination without the requirement of specific sexual structures
Filamentous fungi lifecycle
- Fruitbody releases spores
- Spores germinate, form hyphae in soil
- Mating can occur between hyphae from different spores
- Pinning (young fruitbody)
Vegetative growth of fungi
Fungi typically grow as filaments, termed hyphae
Hyphae
* Classifications
- Septate: In segments, cytoplasm not continuous
- Coenocytic: No divisions, cytoplasm continuous (allows organelles to move through)
How do hyphae grow?
Aprical growth
* Entend only at their extreme tips
* Does branching at the tips
Mycelium
Fungal hyphae branch repeatedly behind their tips, forming a network
Aspergillus nidulans
* Lifecycle
- Sexual cycle
- Asexual cycle
- Parasexual cycle
Aspergillus nidulans
* Sexual cycle
- Hyphae interact (with itself or with others)
- 2 nuclei of different mating types fuse together (diploid)
- Meiosis occurs (forms 4 spores)
- Mitosis occurs (forms 8 spores, known as ascospores)
Aspergillus nidulans (sexual cycle)
* Structure of ascospore
- Ascospores are housed in the ascus
- Surrounded by Cleistothecium
- Hulle cells on the surface of cleistothecium
Aspergillus nidulans (sexual cycle)
* Does Aspergillus nidulans have sex?
No, they have mating types
Aspergillus nidulans (asexual cycle)
- Hyphae forms a type of structure
- Mitosis forms haploid spores
- Spores can grow anywhere
Aspergillus nidulans (asexual cycle)
* What is the structure formed by hyphae known as?
Conidiophore
Aspergillus nidulans (asexual cycle)
* What are the haploid spores formed by conidiophores known as?
Conidium
Aspergillus nidulans (parasexual cycle)
- 2 mating types fuse together (diploid)
- Undergo chromosome loss until it becomes haploid again
When do fungi undergo sexual reproduction?
At a certain threshold when nutrients become somewhat limited and it needs to be more diverse to survive
Yeasts
* Proportion of population
* Morphology
- ~1% of described fungi
- Single celled
Types of yeast
- Fission yeast: Binary fission
- Budding yeast: Parent cell where daughter cells bud off
Some yeasts are dimorphic, how do they appear?
Can switch between yeast phase and a hyphal phase
* Forms pseudohyphae
* Repeated budding forms hyphae like structures
Saccharomyces cerevisiae life cycle
- Asexual reproduction
- Sexual reproduction
(budding yeast)
Saccharomyces cerevisiae (asexual reproduction)
- Two different mating types
- Can interchange between mating types
- Budding off to form new cells
Saccharomyces cerevisiae (asexual reproduction)
* What mating types are there?
a and α
Saccharomyces cerevisiae (sexual reproduction)
- a and α mating type cells form projections towards each other
- Nuclear fusion (diploid, creates a zygote)
- Meiosis (creates 4 daughter cells, 2 a and 2 α)
Saccharomyces cerevisiae (sexual reproduction)
* What are the cells with projections known as?
* What is the process of forming projections known as?
- Schmoo cells
- “Schmooing”
Saccharomyces cerevisiae (sexual reproduction)
* Do zygotes always undergo meiosis?
They can undergo mitosis and produce more zygotes before undergoing meiosis (in this case, by budding)
Saccharomyces cerevisiae (sexual reproduction)
* When daughter cells are formed, what is the structure?
- Surrounded by ascus
- Forms ascospores
Schizosaccharomyce Pombe
* Lifecycle types
* Difference from S. cerevisiae
- Asexual + Sexual
- Undergoes binary fission instead of budding
Why do fungus undergo sporulation?
(6)
- Dissemination
- Reproduction
- Allows fungus to move to new food source
- Allows fungus to survive periods of adversity
- Introduce new genetic combinations into a population
- Source of inocula for infection
What benefits do fungi give us?
(6)
- Nutrient cycling
- Carbon cycling and climate regulation
- Nutrition and food security
- Human health
- Environmental protection
- Sustainable materials
What is yeast used for in food production?
- Baking
- Making lacoholic beverages
What is the the most common yeast used in breadmaking?
Saccharomyces cerevisiae
What do yeast do in baking and making alcoholic beverages?
Ethanol fermentation
In breadmaking, what affects the speed of fermentation?
- Increase speed: Sugar and eggs
- Decrease speed: Fats and salt
What happens to the ethanol produced during fermentation in breadmaking?
Gets evaporated when bread is baked
What types of beers are made by different types of yeast?
- Ale-type beers: Top-fermenting yeast (Saccharomyces cerevisiae etc.)
- Lagers: Bottom-fermenting yeast (Saccharomyces pastorianus etc.)
How is sparkling wine made?
Further adding yeast to the wine when it is bottled
* CO2 formed in this second fermentation is trapped as bubbles
What types of cheese require filamentous fungi to make and ripen?
- Blue-veined cheese (Roquefort, Gorgonzola, Stilton etc.)
- Soft-ripened cheese (Brie, Camembert, Humboldt Fog etc.)
How was Quorn developed?
Believed there would be a shortage of protein-rich foods in 1960s
* Produced commercially from chemostat cultures of mycelium from filamentous fungus
What fungus is used to produce mycoprotein (Quorn)?
Fusarium venenatum
