Lecture 17: Fungi I Flashcards
The drug penicillin comes from which microorganism?
The mold Penicillium
How many fungal species have been described to date?
100,000
How many new fungal species are discovered every year?
1,700
What percentage of fungal species have been identified?
<7%
Name the 6 major characteristics of fungi.
- Eukaryotic
- Chitin cell walls
- Reproduction by spore formation
- Unicellular (round yeast cells) and multicellular structures (hyphae)
- Heterotrophic
- Mostly nonmotile
What is the most common form of spore dissemination?
WInd
What is the thallus?
The fungal body - a large single cell
What are hyphae?
They are filamentous tubular structures with internal septa (sometimes) and multiple nuclei
What are the two types of hyphae (in terms of structure)?
Septate hyphae: have cross-walls, which allow the cytoplasm to flow through
Coenocytic hyphae: do not contain septa
What is mycelium?
It is a group/mass of hyphae, often used interchangeably with hyphae.
What are the two types of hyphae (in terms of function)?
Vegetative hyphae: obtain nutrients
Aerial hyphae: involved in reproduction
Hyphae that extend above the surface produce […] called […]
Spores called conidia
Describe two characteristics of conidia spores.
They are pigmented and resistant to drying.
Describe the reproductive cycle of conidia.
Reproduction is asexual. The conidia (spores) fly off and germinate. They eventually land elsewhere and grow a new hyphae, which then grow new conidia.
What are the three types of fungal morphology?
Yeast, mold, or dimorphic
Describe yeast morphology.
It is non-filamentous, unicellular fungi that are typically oval or spherical
What are the two types of yeast? Explain the difference between them.
Fission yeast: divide evenly to produce two new cells
Budding yeasts: divide unevenly, yielding a bud smaller than the parental cell
What are pseudohypha? When do they occur?
Some yeasts produce buds that fail to detach themselves. This occurs when there’s a limitation in conditions, such as nitrogen starvation.
Name two factors that can affect the formation of pseudohyphae in yeast.
CO2 concentration and nutrient (nitrogen) limitation
Describe the morphology of mold.
Multicellular fungi that grow in hyphae, either septate or aseptate.
What are dimorphic fungi? What can determine their form?
Fungi that can grow either as a mold or as a yeast depending on the temperature conditions. At 37 degrees, it is yeastlike, and at 25 degrees it is moldlike. It can also depend on CO2 concentration.
Describe how dimorphic fungi reproduce.
When in moldlike form, they reproduce with hyphae. When in yeastlike form, they reproduce by budding.
Name 4 important functions of fungi.
Biodegradation, industrial production of enzymes/chemicals/antibiotics, food industry (mushrooms/yeast/cheeses)
Name 4 negative impacts of fungi.
Infection, intoxication, allergy, and degradation
What phylogenetic tree is fungi the most closely related to?
Animals
How do fungi compare with animals in terms of:
a) Motility
b) Consumption of nutrients
c) Membrane content
d) Reproduction
e) Nucleus
a) Fungi are largely non-motile
b) Fungi digest then absorb (exophagous) rather than absorb then digest
c) Membranes contain ergosterol instead of cholesterol
d) Reproduce asexually instead of sexually
e) Nucleus is small with minimal DNA
How do fungi compare with plants in terms of:
a) Cell wall
b) Energy generation
c) Vascular structures
d) Storage carbohydrates
e) Genetics
a) Made of chitin instead of lignin/cellulose
b) No photosynthesis or chloroplasts - don’t make their nutrients
c) No vascular structures
d) Make glycogen as a storage carbohydrate
e) Closer genetically to animals
The classification of fungi is based on […]
Their sexual cycle
The vast majority of fungi belong to which taxonomic groups?
Ascomycota and basidiomycota
What are ascomycota?
A large and diverse group of fungi that includes yeasts and mold
What are basidiomycota?
They include fungi that form mushrooms
The asexual form of fungi is called […], while the sexual form is called […]
Anamorph, teleomorph
What are the two types of teleomorphs? Explain the difference between them.
Homothallic: mating can occur between the hyphae of the same mating type or same thallus
Heterothallic: mating occurs between two different thalli or mating types.
Describe the major characteristics of anamorph spores and give an example.
They are formed by the hyphae of one organism and are identical to the parent. For example, conidia are asexual spores.
How are anamorph spores produced (in general)?
They are produced from a single fungus through mitosis and cell division.
Name the 5 possible forms of asexual spores.
- Not enclosed in a sac
- Fragementation of the septate hyphae
- Buds off the parent cell
- Spore within a hyphal segment
- Enclosed in a sac
How are sexual spores formed (in general)?
From the fusion of two mating strains.
Name the 3 phases of reproduction in sexual spores and explain them.
Plasmogamy: haploid donor cell nucleus penetrates the cytoplasm of the recipient cell.
Karyogamy: the nuclei fuse together and form diploid zygote
Meiosis: the diploid nucleus separates and produces haploid nuclei with a mix of genes from the parent hyphae
Name 2 advantages of sexual reproduction.
- Produces recombinant progeny more fit to the environment
- Purges the genome of deleterious mutations
Name 3 disadvantages of sexual reproduction
- Requires time and energy to find a partner
- Only 50% of parental genes are transmitted to offspring
- Valuable genetic combinations may be broken apart.
What type of fungus is cordyceps? Where is it found?
It is a mold that lives on the jungle floor.
How does cordyceps disseminate?
Its spores infect ants on the ground.
What is the impact of cordyceps on ants?
It infects their brain and changes their behaviour, causing them to leave the colony and climb to the top of the forest canopy. They drive their mandibles into the plant stalk and die.
