Phylum Oomycota Flashcards
What superphylum do Oomycota belong to?
Stramenopiles (heterokonta)
What is the common term for the organisms in the Oomycota phyla?
water moulds
What is the major characteristic of Oomycetes?
they have 2 flagella
What are the other phyla in the Heterokonta superphylum?
Hyphochytriomycota (a very small group of single flagellum organisms)
What type of environments are Ooymcetes found in?
they are water moulds so aquatic - both fresh water, marine and damp soil
What type of life cycles do they exhibit?
saprophytes
parasite
pathogens (many economically important ones)
T or F: Oomycetes have known symbionts
false
What is the major characteristic that distinguishes Oomycetes from true fungi?
they have motile zoospores with 2 flagella
What types of flagella do their zoospores have?
one tinsel and one whiplash
Where on the zoospore cell do the flagella arise?
from the side of the cell (as opposed to the front or back)
Describe tinsel flagellum
Oomycetes have motile zoospores with 2 flagella - one is tinsel:
tinsel flagellum point forwards and have lateral branches (mastigonemes) that PULL the zoospore through water
describe whiplash flagellum
Oomycetes have motile zoospores with 2 flagella - one is whiplash:
whiplash flagellum point backward and have no ornamentation but they PUSH the cell through water
Describe the filamentous growth of Oomycetes
they have highly branched, non-septate vegetative (coenocytic) DIPLOID hyphae that colonize OM or a host
they form mycelia with cellulose and glucans in the cell walls
Describe Oomycete asexual reproduction
asexual reproduction occurs via sporangia, resting spores and/or zoosporangia that produce zoospores with 2 flagella
Describe Oomycete sexual reproduction
Sexual reproduction can occur via the fusion of NON-MOTILE female gametes (oogonia) and male antheridia (much smaller gametes) either on the same mycelium or a different mycelium depending on species to form a zygote
zygote = thick-walled oospore that can persist until conditions are ideal
What are oogonia?
the very large, non-motile female gametes of Oomycetes
What are antheridia?
the smaller male gametes of Oomycetes
What does homothallic mean?
sexual reproduction occurs on the same mycelium - ie., a single mycelium produces both male antheridia and female oogonia
What does heterothallic mean?
compatible gametes for sexual reproduction (male antheridia and female oogonia) are produced on different mycelium
What are the structures involved in asexual reproduction for Oomycetes?
either:
sporangia
resting spores
zoosporangia that produce zoospores
what is an oospore?
the thick-walled persistent (can overwinter or wait until ideal conditions) product (zygote) of sexual reproduction in Oomycetes
What are two major orders of Oomycetes?
Saprolegniales (water molds)
Peronosporales (downy mildew)
Describe saprolegniosis of fish and an example of species that causes it
caused by species of the Saprolegniales (water mold) order, example: Saprolegnia parasitica
an opportunistic parasite or pathogen of freshwater fish such as salmon or trout and amphibians
infects host around mouth, gills and fins or eggs
usually infects unhealthy hosts or hosts with other stressors like aquaculture or hatcheries; life stage and living conditions also affect susceptibility
What conditions are prone to saprolegniales break outs? how is this related to the method of dispersal for Saprolegnia parasitica?
fisheries/hatcheries or aquaculture where fish are under other stressors and more vulnerable to infection
Saprolegnia parasitica disperses by its motile zoospores that swim in water = easily infects multiple individuals and spreads
