Lecture 23 Cellular Slime Molds

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Slime Molds Part I: 

Slime Molds Part I General Mycology Pl P 421/521

Kingdom Protoctista: 

Kingdom Protoctista Phyla of slime molds: Plasmodiophoromycota—endoparasitic slime molds Dictyosteliomycota—cellular slime molds Acrasiomycota—cellular slime molds Myxomycota—plasmodial slime molds

Slime molds: 

Slime molds An organism that produces a trophic stage that lacks a cell wall; phagotrophic Trophic stages: amoebae plasmodia

Amoeba or plasmodium?: 

Amoeba or plasmodium? Amoebae are uninucleate Plasmodia are multinucleate Both lack cell walls, engulf food, and can multiply http://www.planet-pets.com/plntamba.htm

Phylum Plasmodiophoromycota: 

Phylum Plasmodiophoromycota Endoparasitic slime molds Trophic stage formed inside host cells Obligate endoparasites of aquatic and terrestrial plants, algae and fungi 46 species in 16 genera Genera based on arrangement of cysts inside host cells Cause abnormal enlargement of host cells (hypertrophy) or abnormal multiplication of cells (hyperplasia); may also cause stunting

Infection Process: 

Infection Process

Plasmodiophora life cycle: 

Plasmodiophora life cycle Plasmodium develops in host cell with cruciform nuclear divisions Intracellular plasmodium develops into either multilobed sporangium (mitotic process) or cystosorus (meiosis) Zoospores or cysts released from host cell

Cruciform nuclear division: 

Cruciform nuclear division



Plasmodiophora brassicae: 

Plasmodiophora brassicae Described by M. Woronin (1877) Causes club root of crucifers Up to 10% of crucifer acreage worldwide is infested

Spongospora subterranea: 

Spongospora subterranea

Haptoglossa, an enigma: 

Haptoglossa, an enigma From http://www.uoguelph.ca/~gbarron/





Cellular Slime Molds: 

Cellular Slime Molds Two phyla Dictyosteliomycota (dicytostelids) Primarily in soil Acrasiomycota (acrasids) On dead plant parts, tree bark, dung and soil Trophic stage comprises uninucleate cells (myxamoebae) that aggregate


Dictyostelids Three genera, 50 species First discovered in 1869 by Oskar Brefeld Dictyostelium discoideum isolated by Kenneth Raper (1935) important model organism for study of cytokinesis, signalling, chemotaxis, phagocytosis, motility, cell sorting, cell-type determination See DictyBase http://dictybase.org/dicty.html



Dictyostelium life cycle: 

Dictyostelium life cycle Free-living, uninucleate haploid myxamoebae with filose pseudopodia emerge from spores www.image1.com/images/ timelapse-movie.gif

Dictyostelium life cycle: 

Dictyostelium life cycle Myxamoebae aggregate in response to chemical signal (acrasin; cAMP); aggregating amoebae adhere end-to-end www-biology.ucsd.edu/labs/ loomis/agg-stream2.jpeg

Dictyostelium life cycle: 

Dictyostelium life cycle Pseudoplasmodium (non-feeding stage), also called grex or slug, formed of 10- to 50,000 individual amoebae encased in cellulose sheath Migrate in response to temperature, light, relative humidity www.germany-info.org/relaunch/ education/new/edu_genome.html

Life cycle continued: 

Life cycle continued Culmination results in formation of sorocarp http://niko.unl.edu/bs101/pix/dd1.gif

Life cycle continued: 

Life cycle continued Spores disseminated by water, animals Sexual reproduction by macrocysts Zygote attracts and engulfs surrounding amoebae, forming a giant cell with a surrounding sheath


Cells in anterior direct the pseudoplasmodium, but are destined to become stalk cells Cells in posterior will become spores Direction of movement of pseudoplasmodium Cellulose sheath secreted by amoebae Spores

Dictyostelid life cycle: 

Dictyostelid life cycle http://www.zi.biologie.uni-muenchen.de/zoologie/dicty/dicty.html

Genera of Dictyostelids: 

Genera of Dictyostelids Dictyostelium Cells trapped in stalk; one cluster of spores per sporocarp Polysphondylium Cells trapped in stalk, spores forming in whorls along sporocarp Acytostelium No cells trapped in stalk during sporocarp formation


Dictyostelium Polysphondylium


P. Schaap et al., Science 314, 661 -663 (2006) Fig. 1. A universal phylogeny of the Dictyostelia based on SSU rDNA sequences Published by AAAS


Acrasids Three families, five genera, 15 species Polyphyletic Both flagellate and non-flagellate families One family has tubular mitochondrial cristae, the others have plate-like cristae

Acrasid life cycle: 

Acrasid life cycle Germination to release lobose amoeba cytokinesis aggregation Sporocarp formation spores


Acrasids Primarily associated with plant material Lobose pseudopodia on myxamoebae Biflagellate cells in some taxa Aggregation of myxamoebae does not involve cAMP No migration of pseudoplasmodium All cells of sorocarp able to germinate No known sexual reproduction

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