Slime Molds Part I

1. Slime MoldsPart I General Mycology Pl P 421/521

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

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

4. 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

5. 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

6. Infection Process

7. 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

8. Cruciform nuclear division

9. Sporosori

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

11. Spongospora subterranea

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

13. http://www.uoguelph.ca/~gbarron/

14. http://www.uoguelph.ca/~gbarron/

15. 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

16. 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

17. http://web1.manhattan.edu/fcardill/plants/protoc/dicty.html

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

19. 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

20. 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

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

22. 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

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

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

25. 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

26. Dictyostelium Polysphondylium

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

28. 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

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

30. 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