Chytridiomyctoa Flashcards
Chytrids diversity
Over 900 species in 5 orders
Chytrids habitat
Mostly grown aerobically in soil, mud or water, some species inhabit estuaries and others the sea.
Life styles of Chytrids
Mostly saprotrophs: breakdown of materials that decompose plants and animals
Parasites of terrestrial fungi, filamentous algae and diatoms or vascular plants
Pathogens of freshwater invertebrates like larval mosquitos
Obligate anaerobes: grow in rumen of herbivorous mammals and breakdown cellulose
How do Chytrids reproduce
Reproduce by zoospores with a single posterior flagellum except order Neocallimastigales which are multiflagellate
Chitin
Within cell walls of most chytrids species and Eumycota
Consists of chitin microfibrils
Phylum chutridiomycota can have what in their cell walls
Chitin and cellulose
Thallus morphology of Chytrids
Form of thallus is varied:
Holocarpic: within parasitic species-whole thallus is contained within the host cell, no differentiation into vegetative and reproductive parts. At maturity, the entire structure except cell wall which surrounds it, is converted into reproductive units (zoospores, gametes or resting sporangia)
Eucarpic: Thallus differentiated into reproductive (sporangia and resting sporangia) and vegetative organs (rhizoids, rhizomycelium)
Mono centric forms include:
Endo biotic: entire thallus inside host cell
Epibioitc: rhizoids inside host cell and sporangium external
Eucarpic thalli have one or several sporangia: ______ vs ______
Mono centric
Poly centric
Inoperculate Chytrids
Operculate chytrids
Sporangium forms a discharge tube which penetrates host cells
Tip of discharge tube breaks open at a like of weakness and is seen as a special cap or operculum after discharge
Two features of taxonomic importance for chytrids
Flagellar apparatus
Micro body lipid globule complex
Whiplash flagellum on chytrids is made up of what parts
Axoneme: made up of nine doublet pairs of microtubules surrounding two central microtubules
Kinetosome: at the base generates flagellum
Remainder of second kinetosome in some suggests that ancestors of chytridiomycota may have had biflagellate zoospores
Movement variation of chytrids
Period of zoospore movement varies:
-swim for minutes to hours -> Amoeboid crawling
-prior to germination: zoospore rests and encysts->flagellum contracts or casts off
-zoospores encysts on the host surface (Holocarpic groups): cytoplasmic contents of zoospore injected into host
When are fossils of chytrids found and what did they look like
Devonian age: 400mya
-clusters of Holocarpic endobiotic thalli resembling the modern chytrids found inside algae cells-> chytrids were aquatic parasites
-fungi probably emerged from water, as did plants and vertebrates
Largest order of chytrids
And it’s lifestyle
Order Chytridiales (50%)
Parasitic on fungi, algae, protozoa
How can you bait chytrids
Baited in crude culture by floating baits (cellophane, hair, shrimp exoskeleton, booed grass leaves and pollen) on surface of water overlying samples of soil, mud or pieces of aquatic plant material
Asexual reproduction of Chytridiales
-Haploid, uniflagellate zoospores swim to substrate
-zoospores attach producing rhizoids: delicate hypha-like filaments with protoplasm but without nuclei
-zoospore develops into sporangium
-multinucleate protoplasmic sporangium cleaves at operculum to release zoospores
-zoospores swim away completing asexual cycle
Haploid zoospores of Chytridiales can also develop into ______
Sexual thalli
-rhizoids if compatible thalli come into contact
-protoplasm of each thallus streams towards point of fusion (plasmogamy)
-resting body is formed from protoplasts of each thallus, leaving them empty
-Karyogamy converts resting body into zygote
Zygote-> sporangium-> haploid zoospores released into water
Synchytrium sp. causes what diseases and are what type of parasites
Potato wart
Black scab disease
Endobiotic, Holocarpic parasites of algae, mosses, ferns and flowering plants
Typically cause galls (hypertrophied growth) on the diseases parts
Synchytrium resting winter sporangia and summer sporangia
In the spring, resting winter sporangia in decaying warts and soul germinate to realize haploid zoospores
Zoospores migrate in soil water (50mm or less) to infect epidermal cells of sprouting potatoes
Zoospores are short lived and then encyst infected host tissue in 1-2 hours
Host cells engage: Sori form inside host cells (warty galls)
Each sorus contains summer sporangia-> germinate to produce new haploid zoospores which reinfect susceptible tissue
When do testing spores of Synchytrium form
Under conditions of stress (water shortage)
-zoospores fuse->diploid, biflagellate zygotes-> infect the host tissue to form resting sporangia
Resting sporangium of Synchytrium remain viable how long?
How are the spores spread
40-50 years in soil
Resting sporangia spread in infected seed tubers, infected soil and equipment
Order Neocallimastigales inhabit where?
Ruminant animals: aquire nutrients from plant-based food by fermentation in a rumen (specialized stomach) prior to digestion, principally through microbial actions
-rumen fungi inhabit the gastrointestinal tract of ruminants.
-microbes include bacteria, protozoa and 8% fungi by weight
These fungi are adapted for anaerobic conditions
Gut or rumen fungi produce what?
Broad range of hydrolase enzymes and include the most active hemi cellulases that break down cellulose
Allows ruminant animals to break down cellulose
Among these carbohydrate types, which is easiest to digest in which is the least?
Sugars, starches and pectin
Hemicellulose and cellulose
Lignins
Sugars first 95-100% digestibility
Cellulose second
Lignin only 0-20% digestibility
What order of fungi has caused a decline in frog populations
Rhizophydiales
Batrochocytrium dendribatidis has cussed global amphibian decline
How does order Rhizophydiales work to decline amphibian populations
-fungus invades top layers of skin cells and causes thickening of the keratinized layer
-disrupt breathing, balance of sodium and chloride ions in blood leading to heart beat irregularities and stopping
-zoospores swim out through a discharge tube (inoperculate chytrid) and the empty sporangia remain
Amphibian chytrid life cycle
Spores swim towards frogs
Spores burrow into skin and develop into thallus
Mature fungus develops into sporangium
Spores released after 4-5 days
Infected frog died in 120 days
_______ is the first chytrid fungus known to parasitize vertebrate animals
Batrachochytrium dendrobatidis (Bd)
Why did Bd spread so quickly around the world
Human pregnancy tests developed using female frogs in 1930’s. Resulted in massive export of the frogs to labs around the world, to produce home pregnancy tests. Bd may have orijgnallt spread from lab to wild frogs through water the frogs were housed in.
X. laevis (frogs used in pregnancy tests) have been exposed over a long enough euros to Bd that they have developed…..
Defensives against Bd chytridiomycosis
Chloramphenicol
Antibiotic useful for the treatment of a number of bacterial infections used as eye ointment to treat conjunctivitis, may be a lifesaver for the amphibians
Infested frogs bathed in the solution recovered and became resistant to the killer disease: Chytridiomycosis
Most true chytrids produce _____ mycelium
Water molds (Allomyces) makes ______ mycelium
Limited
Extensive
Like the chytrids, water molds are the only members of the fungi in which _______ has been retained
Motility
Summer sporangia characteristics
No thick cell wall
Not a resting spore-just produce more zoospores
Chytrids help with cellulose and hemicellulose breakdown from what pH range
7-5
A thick outer wall indicates what?
Resting spore!!! For winter survival
