Mycology I Flashcards
What is studied in ‘mycology’?
The term “mycology” is derived from Greek word “mykes” meaning mushroom. Therefore, mycology is the study of fungi.
What are the beneficial effects of fungi?
- Decomposition - nutrient and carbon recycling.
- Biosynthetic factories. The fermentation property is used for the industrial production of alcohols, fats, citric, oxalic and gluconic acids.
- Important sources of antibiotics, such as Penicillin.
- Model organisms for biochemical and genetic studies.
- Saccharomyces cerviciae is extensively used in recombinant DNA technology, which includes the Hepatitis B Vaccine.
- Some fungi are edible (mushrooms).
- Yeasts provide nutritional supplements such as vitamins and cofactors.
- Penicillium is used to flavour
cheeses: Roquefort and Camembert. - Fungi (Leptolegnia caudate and Aphanomyces laevis) are used to trap mosquito larvae in paddy fields and thus help in malaria control.
What are the harmful effects of fungi?
- Destruction of food, lumber, paper, and cloth.
- Animal and human diseases, including allergies.
- Toxins produced by poisonous mushrooms and within food (Mycetism and Mycotoxicosis).
- Plant diseases.
- Spoilage of agriculture produce such as vegetables and cereals in the godown.
- Damage the products such as magnetic tapes and disks, glass lenses, marble statues, bones and wax.
What are the general properties of fungi?
- eukaryotic + exhibit mitosis.
- ergosterols in membranes + 80S ribosomes.
- rigid cell wall –> non-motile, (cell wall = chitin).
- chemoheterotrophs and lack chlorophyll–> not autotrophic.
- osmotrophic; (obtain nutrients by absorption).
- saprophytes (live off of decaying matter) or as
parasites (live off of living matter). - require water and oxygen (no obligate anaerobes).
- reproduce asexually and/or sexually by producing spores.
- grow reproductively –> budding or non-reproductively –> hyphal tip elongation.
- food storage = form of lipids and glycogen.
What feature seperates fungi from animal cells?
rigid cell wall –> non-motile
cell wall is made from CHITIN!
What is the nutrition type of fungi?
HETEROTROPHIC
- chlorophyll deficient plant
- cannot manufacture carbohydrates (using carbon dioxide, water and sunlight).
- simple structural organization –> always depends on dead or living organic matter for their energy requirements
How are fungi classified on the basis of mode of nutrition?
1) Saprophytes - nutrition from dead organic matter.
2) Parasites - food from other living plants or animals.
3) Symbionts - grow on or with another living organism, but both are mutually benefited.
4) Predacious Fungi - animal capturing fungi (predators).
Explain fungus growth.
1) fungal spores germinate and form
hyphae.
2) the spore absorbs water through its wall, the cytoplasm activates, nuclear division occurs, and more cytoplasm is
synthesized.
3) The wall initially grows as a spherical structure.
4) Once polarity is established, a hyphal apex forms, and from the wall of the spore
a germ tube bulges out, enveloped by a wall of its own that is formed as the germ
tube grows.
5) The growing tip eventually gives rise to a branch. This is the beginning of the
branched mycelium.
How many regions may the hypha be divided into? What are they?
- the apical zone about 5–10 micrometers n length,
- the subapical region, extending about 40 micrometres back of the apical zone, (rich in cytoplasmic components but devoid of vacuoles)
- the zone of vacuolation, presence of many vacuoles and the accumulation of lipids.
What is a hypha?
the structure formed from germinating spores
What is present in the subapical region of hyphae?
CYTOPLASMIC COMPONENTS eg. nuclei, Golgi apparatus, ribosomes, mitochondria, the endoplasmic reticulum, and vesicles.
NO VACUOLES!
How do fungi secure food?
digestion of food: action of enzymes (biological catalysts)
absorbtion of food: directly through the hyphal walls.
Food must be in solution in order to enter the hyphae, and the entire mycelial surface of a fungus is capable of absorbing materials dissolved in water.
Explain the classification of fungi.
Fungi is one of the 5 kingdoms.
What are the 5 kingdoms?
Monera, Protista, Fungi, Plantae and Animalia
How are fungi classified based on sexual reproduction?
- Zygomycetes: reproduce through zygospores.
- Ascomycetes: produce endogenous spores called “ascospores” in cells called asci.
-
Basidiomycetes: produce exogenous spores called “basidiospores” in cells called
basidia. -
Deuteromycetes (Fungi imperfecti): do not produce any sexual spores (ascospores or basidiospores).
- heterogeneous group of fungi where no sexual reproduction has yet been demonstrated.
How are fungi classified based on morphology?
- Moulds (Molds): Filamentous fungi Eg: Aspergillus spp., Trichophyton rubrum.
- Yeasts: Single celled cells that buds Eg: Cryptococcus neoformans, Saccharomyces cerviciae
- Yeast like: Similar to yeasts but produce pseudohyphae Eg: Candida albicans
-
Dimorphic: Fungi existing in two different morphological forms at two different environmental conditions.
(yeasts in tissue (in vitro at 37 C) and moulds (in natural habitat and in vitro at room temperature). Eg: Histoplasma capsulatum
Explain the life of dimorphic fungi.
YEAST in tissue (in vitro at 37 C)
MOULDS in natural habitat (in vitro at 21 C)
State the morphology of fungi. In what 2 fundamental forms do fungi exist in?
exist in two fundamental forms:
1) the filamentous (hyphal) form
2) single celled budding forms (yeast).
For the classification’s sake they are studied as molds, yeasts, yeast like and dimorphic fungi.
All fungi have typical eukaryotic morphology.
- rigid cell wall composed of chitin, (may be layered with mannans, cellulose, glucans and other polysaccharides in association with polypeptides)
- can possess polysaccharide capsules that help them to evade phagocytosis.
State examples of fungi that possess polysaccharide capsules.
Cryptococcus and yeast form of Histoplasma capsulatum
What is the thallus of mold made of? What is its structure?
made of hyphae: cylindrical tube like structures that elongates by growth at tips.
What is the mass of hyphae known as?
mycelium
What is responsible for the filamentous nature of mold?
hypha
How can hyphae be different?
branched/unbranched
seotate/aseptate
What are the cross walls of hyphae called, that divie them into numerous cells?
septa
What do septa of hyphae possess? What does this allow for? What does this cause fungi to be?
septa have small pores through which cytoplasm is continuous throughout the hyphae.
all hyphal fungi tend to be COENOCYTIC (multinucleate).
Are most molds septate or aseptate? Exeption?
all molds are SEPTATE exception: zygomycetes (Rhizopus, Mucor)
What is considered more primitive? septate or aseptate? Why?
Non-septate hyphae because if a hyphal strand is damaged the entire strand dies.
What happens when a septate hyphal strand is damaged?
The pores betwee adjacent compartments can be plugged, thus preventing death of the whole hyphal strand.
What are the three kinds of mycelium?
1.Vegetative mycelium: penetrates the surface of the medium and absorbs nutrients.
2. Aerial mycelium: grow above the agar
surface.
3. Fertile mycelium: aerial hyphae that bear reproductive structures such as conidia or sporangia.
How does vegetative mycelium look?
root-like structure of a fungus consisting of a mass of branching, thread-like hyphae.
What does mycelium impart to the colony?
colour, texture and topography
What is the structural unit of mold?
hypha
What do fungi possess which have colonies that are coloured grey, black or olive? What are they called?
melanin pigments –> called phacoid or dematiaceous
What are hyphae called that dont possess any pigments in their cell wall?
Hyaline
What can hyphae have that aids in their identification?
specialized structures:
a) Spiral hyphae: spirally coiled hyphae commonly seen in Trichophyton mentagrophytes.
b) Pectinate body: short, unilateral projections from the hyphae that resemble a broken comb.
Commonly seen in Microsporum audouinii.
c) Favic chandelier. group of hyphal tips collectively resembling a chandelier or the
antlers of the deer (antler hyphae).
They occur in Trichophyton schoenleinii and Trichophyton violaceum.
d) Nodular organ: enlargement in the mycelium that consists of closely twisted hyphae.
Often seen in Trichophyton mentagrophytes and Microsporum canis.
e) Racquet hyphae: regular enlargement of one end of each segment with the opposing end
remaining thin.
Seen in Epidermophyton floccosum, Trichophyton mentagrophytes.
f) Rhizoides: root like structures seen in portions of vegetative hyphae in some members of zygomycetes.
g) structures in the hyphae arising out of modification of single cells and transforming
into thick-walled resting cells.
Chlamydospore (or chlamydoconidia), which are produced by Trichophyton schoenleinii and
Trichophyton verrucosum are thick-walled cells that are larger than other cells and arranged singly or in groups.
What type of cell is yeast?
unicellular spherical to ellipsoid cells
How does yeast reproduce? What does it result in?
budding, which result in blastospore (blastoconidia) formation.
What happens if yeast cell buds fail to detach during budding?
They elongate thus forming a chain of elongated hyphae like filament called pseudohyphae.
What type of yeast has pseudohyphae?
Candia albicans
What is the difference between pseudohyphae and the germ tube?
There is a constriction in pseudohyphae at the
point of budding, while the germ tube has no constriction.
How can polysaccharide capsules present in yeast be demonstrated?
by negative staining methods:
- India ink
- Nigrosin
What do true yeasts not produce?
pseudohyphae
Can yeasts be pigmented?
yes,
eg. Rhodotorula spp. –> pink colonies –> carotenoid pigments.
How do fungi reproduce?
By asexual, sexual and parasexual means.
What is the most common mode of reproduction in fungi?
Asexual reproduction
(fungi participating in sexual mode only under certain circumstances.)
What is the form of fungus undergoing asexual reproduction known as?
Anamorph/imperfect stage
What is the form of fungus undergoing sexual reproduction known as?
teleomorph (perfect stage)
What is the form of fungus undergoing both asexual and sexual reproduction known as?
holomorph
State the process of asexual reproduction in yeast.
Asexual propagules are termed either spores or conidia depending on their mode of
production.
Asexual spores are produced following mitosis where as sexual spores are produced
following meiosis.
The asexual spores of zygomycetes, which are known as sporangiospores form within sac like
structure known as sporangia.
The sporangiospores result from the mitotic cleavage of cytoplasm in the sporangium.
The sporangia are borne on special hyphae called sporangiophore.
This endogenous process of spore formation within a sac is known as sporogenesis.
What is teh name of asexual propulates of yeast?
spores or conidia
(depends on mode of production)
How are asexual spores produced?
mitosis
How are sexual spores produced?
meiosis
What are asexual spores of zygomycetes called? Where do they form?
sporangiospores –> sac structure called sporangia
What do sporangiospores result from?
the mitotic cleavage of cytoplasm in the sporangium
What special hyphae are sporangia borne on?
sporangiophore
What is sporogenesis?
the endogenous process of spore formation within a sac
How do conidia arise?
by budding off conidiogenous hyphae or by
differentiation of preformed hyphae
What do conidia develop from?
mitosis of a parent nucleus and are formed
in any manner except involving cytoplasmic cleavage
What is conidiogenesis?
The making of conidia by budding off conidiogenous hyphae or by differentiation of preformed hyphae. developing from mitosis of a parent nucleus.
Where does conidiogenesis occur?
in yeasts and moulds
What special structures are conidia borne on?
conidiophores
What are the two types of conidia production?
blastic
thallic
Explain the blastic production of conidia.
- conidium enlarges
- septum forms
conidium originates from part of parent
Explain the thallic production of conidia.
conidium is differentiated by a septum before its
differentiation!
–> conidium results from the conversion of entire parent cell into the conidium.
What is a conidiogenous cell? Other name?
The cell that gives rise to a conidium.
conidiogenous cell = phialides
What are conidiophores? What do they bear?
- specialized hyphae
- bear conidia or conidiogenous cells.
Explain sexual reproduction of fungi.
Sexual propagules are produced by the fusion of two nuclei that then generally undergo meiosis.
1) plasmogamy (cytoplasmic fusion
of two cells).
2) karyogamy (fusion of two compatible nuclei), –> diploid/zygote nucleus.
3) genetic recombination and meiosis.
The resulting four haploid spores are said to be sexual spores, e.g. zygospores, ascospores, basidiospores
What is the name of sexual spores?
zygospores/ascospores/basidiospores
Explain parasexual reproduction of fungi.
Involves genetic recombination without the requirement of specific sexual structures.
Where does parasexual reproduction occur?
basidiomycetes,
ascomycetes,
deuteromycetes.
What is teh biological importance of spores?
1) Allows for dissemination
2) Allows for reproduction
3) Allows the fungus to move to new food source.
4) Allows fungus to survive periods of adversity.
5) Means of introducing new genetic combinations into a population.
