Phylum Chytridiomycota & Chytridiomycosis

Question 1

T or F; there is some fossil record of Chytridiomycota

Answer 1

true in the Rhynie Chert in Scotland

Question 2

What are some general features of this phylum?

Answer 2

there are 4 orders

can have motile, asexual zoospores with a single whiplash flagellum

cell walls contain chitin

Question 3

What lifestyles can these fungi have?

Answer 3

saprophytes
parasites
pathogens (few)

utilize many substrates (ex. chitin, keratin, cellulose) and hosts (ex. plants, animals, protists, other fungi)

Question 4

What environments do they live in?

Answer 4

freshwater and semi-aquatic (damp soils)

Question 5

Which life phase (haploid or diploid) is most common?

Answer 5

haploid asexual

sexual stage for most species is not well described or unknown

Question 6

Which is the largest class in the phylum?

Answer 6

Chytridiomycetes

Question 7

What does ‘Chytridion’ mean in Greek? why are they called this?

Answer 7

‘little pot’ because of the shape of their zoosporangium looks like a little cup or pot

Question 8

How can these organisms find new substrates for their growth after reproduction?

Answer 8

they disperse short distances and use chemo- or maybe phototaxis to find new substrates

then rhizoids can attach the germinated zoospore to the substrate

Question 9

What allows Chytridiomycetes to use their substrates?

Answer 9

rhizoids attach a germinated zoospore to a substrate and allow the growing fungus to secrete enzymes for breaking down the substrate into useable nutrients

Question 10

what are the 4 structural features a chytridiomycete may have?

Answer 10

holocarpic - produce one zoosporangium that produces multiple zoospores

eucarpic - produces other structures like rhizoids to attach to a substrate

monocentric - forms one zoosporangium

polycentric - forms more than one zoosporangium on a rhizo-mycelium

Question 11

Where can the thallus be located?

Answer 11

either

epibiotic - on the surface (of the substrate/host I think)

endobiotic - inside the substrate/host

Question 12

What are some examples of Chytridiomycota? what are their structural features?

Answer 12

Spizellomyces palustris - monocentric and eucarpic

Polychytrium aggregatum - polycentric and eucarpic

Question 13

What is the main purpose of rhizoids aka rhizo-mycelium?

Answer 13

they attach the zoosporangium to a substrate and allow it to digest and uptake nutrients

Question 14

What is Chytridiomycosis? What species of Chytridiomycota is involved?

Answer 14

it’s a skin infection of amphibians caused by Batrachochytrium dendrobatidis (Bd)

Bd infects mouths and webbed digits of amphibians until skin keratinizes even more and peels off = causes imbalanced osmoregulation, respiration, and thermoregulation which can lead to death

Question 15

How many species of amphibians are affected by Chytridiomycosis? Where was it first observed? How might it be spreading?

Answer 15

~350 amphibian species globally

observed first in Australia and Panama

has caused serious declines and even extinctions

some frog species are tolerant and may act as vectors

Question 16

How is Bd classified in terms of infectious diseases?

Answer 16

emerging (aka an invasive pathogen) likely because so many species are susceptible, it’s having large effects

Question 17

What are the 2 explanations (hypotheses) for emerging infectious diseases?

Answer 17

1 - NOVEL: pathogen is newly introduced to an area

2 - ENDEMIC: pathogen was always present but conditions have changed to increase its infection rates

Question 18

Which hypotheses likely best explains the sudden and current spread of Bd?

Answer 18

likely the novel pathogen hypothesis

where the hosts are susceptible and the pathogen didn’t exist before

a vector may be involved

why not the endemic hypothesis?
- the pathogen shows very little genetic diversity = hasn’t evolved with these host species over time
- it isn’t just affecting one place, it’s spreading to new locations = multiple introductions

Question 19

Where is Bd thought to have originated from?

Answer 19

amphibian trade from Africa, likely from the African clawed frog as a possible vector

or from the American bullfrog from eastern NA but large part of world amphibian trade and bullfrog farms

Question 20

Which BC amphibian species has highest prevalence of Bd?

Answer 20

Wood frogs, Rana sylvatica

Question 21

Describe the state/history of Bd in BC

Answer 21

found across the entire province

the lineage here is hypervirulent (BdGPL)

probably introduced from the bullfrog trade and now is endemic to BC and Yukon

likely human and bullfrog vectors and waterfowl transmissions

Question 22

How can Bd be mitigated?

Answer 22

increased biosecurity measures and regulations to reduce spread through global trade

screening of trade and commercial frog farms

monitoring wild populations