Ascomycetes Flashcards
What is the difference between ascus and basidium meiospores?
Basidium = spores are borne exogenously
Ascus = spores are borne endogenously
What is a sporangium?
A specialized cell within which spores develop
What types of spores do mitosporangia produce?
Spores developed through mitosis
What type of spores do meiosporangia produce?
Spores developed through meiosis
How are clamps formed in basidiomycetes?
Two nuclei that both need mitotic division
The division leaves a clamp behind
How are croziers formed in Ascomycota?
They are formed immediately before sexual reproduction - don’t last long
How do spores develop in the ascus?
Meiosis yields 4 haploid nuclei in the developing ascus
Post-meiotic mitosis happens directly in the ascus
Goes from 4 to 8 spores
How have asci evolved to eject their spores?
Their walls
Their openings
Terminal Thickenings
What is a prototunicate ascus wall?
Single wall, dissolves when mature
What is a unitunicate ascus wall?
Single wall that can have openings in various locations
What is a bitunicate ascus wall?
2 walls - jack-in-the-box mechanism that facilitates the ejection of the entire spore pack
What is a lid on the ascus referred to as?
An operculum
How are spores actively discharged from asci?
A young ascus is filled with glycogen
As ascospores mature, glycogen is converted in low molecular weight osmolyte
The osmolyte takes up water as the ascospores mature, causing the asci to swell and develop turgor pressure
When a critical point is reached, the ascus bursts
What is a key step in many ascomycete species?
The production of conidia
What are conidia?
Non-motile fungal mitospores that are not formed inside a sporangium
How are conidia produced?
They are borne on conidiophores in/on special receptacles called conidiomata
What is enclosed conidioma referred to as?
Pycnidia
What is cushioned conidioma referred to as?
Sporodochia
What are conidiophores in a broom referred to as?
Synnemata
What are conidia used for?
Asexual reproduction
The self-propagating asexual phase is known as the anamorph
What are the names of fungi that have enclosed and non-enclosed conidiomata?
Enclosed = coelomycetes
Non-enclosed = hyphomycetes
What is the teleomorph form also referred to as?
The meiotic form
What is the anamorphic form also referred to as?
The mitotic form
What did Schwendener do?
He demonstrated that there was no difference between green blobs and free-living algae
Proposed that lichens are made up of two organisms = symbiosis
What does algae do for fungi?
Produce sugars for the fungi to consume
What does fungi do for algae?
Protection from herbivory, fungi produce secondary metabolites that are deterrents to herbivores
What are some common chemical tests to visualize lichen secondary metabolites?
Household bleach (C)
Potassium hydroxide (K)
In general, how are lichen named?
They are given the fungal name
What group are both major symbionts of lichen in?
Polyphyletic groups
What are crustose lichens?
Lichens that are so closely attached to the substrate that they cannot be removed without also damaging the substrate
What are foliose lichens?
Lichens that are flat with an upper surface that is colored differently than the lower surface. Sometimes it has a lower surface with outgrowths called rhizines
What are the forms of fruticose lichens?
Hair-like
Shrub-like
Club-like
If we section through the thallus of a lichen, what do we see?
The upper cortex
The photobiont
The medulla
The lower cortex
How do lichens form?
The fungus forms a thallus with algal cells and loose internal hyphae (medulla)
What type of algae can lichen fungi associate with?
Green algae
Cyanobacteria
Sometimes lichen associated with both and is called tripartite
What describes the horizontal transmission of symbionts?
If the fungus produces spores, then these need to find a suitable photobiont
The fungus and the algae need to meet somehow
What describes the vertical transmission of symbionts?
They can disperse asexually in combined fungal-algal packets
What are some surface modifications that serve for the propagation of lichens?
Isidia
Soredia
What are isidia and where are they found?
It is a vegetation means of propagation
Normally found on the outer cortex of the lichen
Fungal and algal cells are combined in a column-like structure that can break off and establish elsewhere
What are soredia and where are they found?
powdery propagules composed of fungal hyphae wrapped around cyanobacteria or green algae
Can be scattered diffusely across the surface of the lichen’s thallus, or produced in localized structures called soralia
What are the uniting features of non-lichen ascomycetes?
Typically less expansive mycelia than Basidiomycetes
Many are ephemeral (appear and disappear again) and seasonal (unlike most lichens)
Many are pathogens
What phylogenetic group are all ascocarps in?
Polyphyletic
What is apotheciate (cup) fungi?
A cup-shaped ascocarp that is polyphyletic
What is an example of an inside-out Asco?
Devil’s cigar
The ascus and ascospore are pointed inside
Many cup fungi can also have what?
Anamorphs
Which type of fungi have evolved to capture and consume nematodes?
Cup fungi
What do fertile pyrenomycetes possess?
A perithecium
What are the two types of ontogeny that perithecia encompass?
Perithecium
Pseudothecium
What describes perithecium?
The fruiting body forms together with sexual hyphae
What describes pseudothecium?
Fruiting body forms first, followed by the formation of ascus-bearing hyphae
What do some species produce perithecia in?
A stroma where you will see clusters of perithecia
What is found in the ergot life cycle?
The sclerotium and the actual fruiting body is also a peritheciate stroma
What is the sclerotium?
A mass of hyphae with protective rind and containing food reserves
What does the consumption of ergot cause?
Ergotism which causes hallucinations, itching and burning skin, gangrene, and sometimes death
What is ergot the building block of?
LSD
What is a cleistothecium?
An ascocarp that is round and closed and often differentiated into cleistothecia and chasmothecia (in which asci are formed at one level and the globular structure breaks open through a predetermined line of weakness
If the globular case is formed from a net of hyphae, what is it called?
A gymnothecium
How are asci scattered in cleistothecia?
Asci are scattered through the closed case, not embedded in a gel
Which significant fungi do cleistothecium-forming Eurotiomycetes form?
Aspergillus = used in the production of soy sauce
Penicillium = used in the production of cheese and penicillin
How fast does Aspergillus develop?
Mycelia develop conidiophores within 16 hours of germinating, first conidia are dispenses 8 hours later = 24 hour life cycle
What is A. oryzae involved in?
Starch degradation for making sake
Proteolytic and amylolytic activity for two-stage fermentation of soy sauces
What is A. niger involved in?
The production of most of the worlds citric acid
95% efficiency for conversion of sugar to citric acid
When is an ascocarp referred to as a gymnothecia?
When the ascocarp forms an unsealed hyphal wad, the hyphae give rise to asci
What ascomycete is mycorrhizal?
Truffles
What is the exception to the anamorphic/asexual life cycle in yeasts?
Bakers yeast
It does have a sexual stage without a hyphal teleomorph
Which classes are sexual yeasts found in?
Saccharomycetes and Schizosaccharomycetes
What does S. cerevisiae do?
Fermentation of glucose and other sugars via pyruvic acid into ethanol and CO2
What do candida yeasts produce?
Pseudohyphae - yeasts in a chain
What are the characteristics of candida yeasts?
Can grow as true yeasts, true septate hyphae or as pseudohyphae
Pseudohyphae are intermediate between hyphae and yeasts
Candida is one of the few true fungi in which the vegetative state is diploid
What does candida cause?
Candidiasis infections
Where are Metschnikowia yeasts found?
In floral nectar
What happens to Metschnikowia yeasts at high cell densities?
The yeasts will eventually degrade nectar up to the extreme of depleting virtually all of its sugar
They also warm up the flower interior of some winter-flowering plants
What are the characteristics of fission yeasts?
Chitin is present only in traces in the cell wall
It can uniquely split into two equal-sized cells by septation
Distantly related to other years and evolutionarily isolated
It is the fermenting agent of African millet beer and arak
What triggers the hyphal-yeast switch?
Temperature: many pathogens are hyphal at 25 degrees but switch to yeast growth around 37 degrees - causes disease
Changes in the chemical environment, especially nutrient starvation
What triggers the hyphal-yeast switch in Candida?
Switching the environment to neutral or alkaline pH
Carbon starvation
Nitrogen starvation
Cell density via quorum sensing molecules
Low oxygen and elevated CO2
presence of N-acetylglucosamine
What are saprotrophs?
Utilize already dead matter
What do biotrophs consume?
Living organisms
What do hemibiotrophs consume?
Tap into living organisms, continue in dead organisms
What are necrotrophs?
Pathogens which feed by killing hosts
How do anamorphs persist in Ascomycota?
By forming conidia
How do teleomorphs persist in Ascomycota?
By forming asci
What is a holomorph?
A fungus that is characterized by both sexual and asexual reproductive states
How do anamorphs persist in Basidiomycota?
By budding
How do teleomorphs persist in Basidiomycota?
By forming basidia
Is dimorphism related to sex?
NO!
Any anamorph or teleomorph can be either sex type, changing the state does not change the sex
