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Lecture 20�

- Almost Fungi: Oomycota�

- Eumycetozoans (slime molds)�

“Almost Fungi”: Oomycota

- about 700 species in 95 genera and several families and Orders

- morphologically similar to Fungi but always had a controversial classification status: ===> traditionally studied by mycologists

--- Pringsheim 1858 ---> algae --- later included in Fungi --- Kreisel 1969 ---> suggest exclusion from Fungi

Recent molecular phylogenies show no close relationships with Fungi --- uncertain affinities within the kingdom Chromista, class Heteronkonta ----- possibly close to heterokont algae with chlorophyll a and c, suggesting possible secondary loss of photosynthetic pigments.

Why not Fungi? - diploid hyphae - cellulose (mostly beta-glucans, like in Fungi), but not chitin in the cell wall - asexual reproduction by mean of biflagellate zoospores - various biochemical characteristics

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Oomycota

Many Saprolegnia and Achlya species form compatible antheridia and oogonia on the same mycelium, which means that they are homothallic. Since the assimilative thallus is diploid, meiosis must take place inside the gametangia.

From Kendrick

“Almost Fungi”: Oomycota

Two flagella: one tinsel, one whiplash (SEM above) arising from the side of the cell.  - The tinsel bears mastigonemes (“hairs”). - The zoospores swim with their tinsel flagellum pointing forward, while the whiplash flagellum is directed backward. 

From Kendrick

Asexual spores are biflagellate

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Oomycota

Saprolegnia life cycle

From Kendrick

Oomycota

From Kendrick

Pythium - in soil: damping off of seedlings - persist saprobically in most soils - spread by zoospores during wet conditions.

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Oomycota Phytophthora

http://ocid.nacse.org/classroom/fungi/bot461/images/Oomycota/Phytophthora/PinfestanssporangiumLM.jpg

http://www.ag.uiuc.edu/cespubs/pest/articles/images/photocd/phytophtora_rot_of_seedling.jpg

Oomycota

From Kendrick

Phytophthora infestens

potato blight

1845-1847, causing widespread famine in Ireland and UK… this episode led to the founding of the discipline now known as Plant Pathology.

The ravages of potato blight contributed to > 1 million of deaths, and drove millions more to emigrate from Ireland. Ten years after the first epidemic, the population of Ireland had crashed from 8 million to 4 million.

Many families were forced to leave their homes forever.

Many sailed for North America.

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Eumycetozoans: plasmodial and cellular slime molds

Plasmodial ---> Myxomycetes

Cellular, aggregation ----> Dictyostelids

Cellular, no aggregation -----> Protostelids

- amoeba-like trophic stage; - aerial spore-bearing reproductive structures (‘sporocarp’). - widespread and often abundant in nature - predators of other microorganisms (bacteria, yeasts, cyanobacteria and green algae).

Life cycle of plasmodial slime molds (myxomycetes)

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http://www.life.umd.edu/classroom/biol106h/L15/Biol106_L15.html

Life cycle of cellular slime molds

(dictyostelids)

History

Because they form fruiting body-like structure, slime molds have been traditionally studied by mycologists; whether or not they were closely related to the fungi has been controversial.

--- Fries (1821) classified some myxomycetes (e.g., Lycogala) in the gasteromycetes.

--- Heinrich Anton de Bary, 1859: Die Mycetezoen (Germany), considered the Mycetezoa to be more closely related to protozoans than the fungi.

This is one of the least studied group of organisms

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http://slimemold.uark.edu/aboutframe.htm

Phylogeny

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Phylogeny

A molecular phylogeny for the eumycetozoan has still to be developed: -- molecular work has been difficult; -- multiples introns in the ribosomal DNAs; possible paralogues copies or “contaminants” ? (they feed on other protists). -- paralogues found in EF1-alpha genes; -- facultative RNA editing of mitochondrial genes;

==>

However, preliminary data seems to largely agree with traditional taxonomy

Suitable Substrates for Protostelids and Myxomycetes

Bark of living trees Plant litter on the ground Hanging plant litter

Standing dead wood or stumps

Downed and decayed wood or bark

Standing dead herbaceous plant parts such as old inflorescences

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Other Aerial Microhabitats

Large inflorescences of tropical plants Epiphytic moss and algal communities on tree bark

Methods for Isolating Protostelids

Substrates are broken into small pieces and soaked in sterile water.

Then they are arranged on agar containing very low nutrient levels.

Next the plates are scanned to find and identify protostelids.

Schizoplasmodiopsis micropunctata.

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Methods for Isolating Myxomycetes

Moist chambers are prepared with filter paper in a pertri dish.

Substrates are arranged in the chamber and wetted.

Plates are scanned with a stereoscope.

Arcyria denudata.

Substrates for Dictyostelid isolation

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Methods for Isolating Dictyostelids

Part of the sample is weighed. Then the weighed sample is placed in sterile water and diluted and a portion is placed on a plate of Hay Infusion agar.

Plates are scanned with a stereoscope and species are noted.

Some dictyostelids are subcultured for closer inspection and identification.

Some Myxomycetes

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Plasmodium

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http://www.sciencedaily.com/releases/ 2010/01/100121141051.htm

Fruiting Body

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Stipe

Spore Mass

Peridium Capillitium

Capillitium

Spore

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Stemonitales

Liceales

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Trichiales

Physarales

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Some Dictyostelids

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Some Protostelids

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