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
Sporosori: Sporosori
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/
Slide13: http://www.uoguelph.ca/~gbarron/
Slide14: 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: 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
Slide17: http://web1.manhattan.edu/fcardill/plants/protoc/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
Slide23: 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
Slide26: Dictyostelium Polysphondylium
Slide27: 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: 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: 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