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21 Slime Molds
Kingdom Protoctista Phyla of slime molds: Slime Molds 4032604 Lecture 21 Slime molds Plasmodiophoromycota—endoparasitic slime molds Dictyosteliomycota—cellular slime molds Acrasiomycota—cellular slime molds Myxomycota—plasmodial slime molds Amoeba or plasmodium? An organism that produces a trophic (feeding) stage that lacks a cell wall; food is engulfed (phagotrophism) Several different types of wall-less feeding stages are formed by slime molds Amoebae are uninucleate Plasmodia are multinucleate Both lack cell walls, engulf food, and can multiply amoebae plasmodia http://www.planet-pets.com/plntamba.htm 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 Plasmodiophora brassicae Described by M. Woronin (1877) Causes club root of crucifers Up to 10% of crucifer acreage is infested worldwide 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 1 Infection Process Biflagellate zoospores encyst and forms a short germ tube that attaches to host cell wall by appressorium; Cyst differentiates into rohr and stachel; Parasite cytoplasm rapidly injected into host cell; Plasmodium develops in host cell with cruciform nuclear divisions; Intracellular plasmodium develops into either lobed sporangium (mitotic process) or cystosorus (meiosis) Zoospores or cysts released from host cell Infection Process Plasmodiophora life cycle Cruciform nuclear division Spongospora subterranea 2 Zoospores http://www.pa.ipw.agrl.ethz.ch/spongospora/intro.htm Sporosori 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, celltype determination See DictyBase http://dictybase.org/dicty.html Dictyostelium life cycle Free-living, uninucleate haploid myxamoebae with filose pseudopodia emerge from spores www.image1.com/images/ timelapse-movie.gif 3 Dictyostelium life cycle Myxamoebae aggregate in response to chemical signal (acrasin; cAMP); aggregating amoebae adhere endto-end www-biology.ucsd.edu/labs/ loomis/agg-stream2.jpeg Life cycle continued Culmination results in formation of sorocarp Dictyostelium life cycle Pseudoplasmodium (non-feeding stage), also called grex or slug, formed of 10to 50,000 individual amoebae encased in cellulose sheath Pseudoplasmodium migrates in response to temperature, light, relative humidity www.germany-info.org/relaunch/ education/new/edu_genome.html 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 http://niko.unl.edu/bs101/pix/dd1.gif Spores Cells in anterior direct the pseudoplasmodium, but are destined to become stalk cells Cellulose sheath secreted by amoebae Cells in posterior will become spores Direction of movement of pseudoplasmodium http://web1.manhattan.edu/fcardill/plants/protoc/dicty.html 4 Dictyostelid life cycle 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 http://www.zi.biologie.uni-muenchen.de/zoologie/dicty/dicty.html Dictyostelium 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 Polysphondylium Acrasid life cycle Acrasids spores Germination to release lobose amoeba cytokinesis Sporocarp formation 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 aggregation 5 Mycetozoa Slime Molds: Plasmodial Slime Molds A grouping used for cellular and plasmodial slime molds plus protostelids The ninth edition of the Dictionary of Fungi recognizes the cellular slime molds and protostelids in phylum Myxomycota The names Myxomycota and Mycetozoa imply a fungal-like affinity for these protozoans—but where do they belong? Phylum Myxomycota Myxomycetes include 5 orders, 13 families, 62 genera and 800 species Characterized by formation of a plasmodium Multinucleate trophic stage comprised of protoplasm surrounded by thin plasma membrane Engulfs bacteria, fungal spores, small pieces of organic matter Phylogenetic analyses of EF-1 amino acid sequences from Baldauf and Doolittle, 1997. PNAS 94 (22): 12007-12012 Stages in Life Cycle Spores (2nÆn) 4-20 microns, globose, pigmented and ornamented; formed in sporocarp; meiosis occurs in spore resulting in 4 nuclei and 3 degenerate Stages in Life Cycle Swarm cells (n) Uninucleate cells with 1-4 anteriorly inserted whiplash flagella and amoeboid posterior; capable of feeding (absorbing and engulfing), and can function as gametes but cannot undergo http://www.botany.hawaii.edu/faculty/wong/Bot201/Myxomycota/S warm_Cells2.jpg cell division 6 Stages in Life Cycle Stages in Life Cycle Zygote (2n) Myxamoebae (n) Formed by fusion of two myxamoebae or swarm cells; begins engulfing food and enlarges through repeated, synchronous nuclear division Uninucleate amoeboid cell emerging from spore; capable of feeding, cell division, and can function as gametes; form microcysts under adverse conditions Plasmodium (2n) Multinucleate, wall-less protoplasm, often exhibiting reversible streaming to translocate food particles that are engulfed at leading edge Photo by Stephen Sharnoff www.uoguelph.ca/~gbarron/ MISCE2002/myxamo2.jpg Physarum life cycle Stages in Life Cycle meiosis Sclerotium (2n) Resistant stage formed by plasmodium under adverse conditions karyogamy microcyst Sporophore (2n) Synchronous mitotic divisions Entire plasmodium is converted into one or many sporophores, depending on taxa macrocyst Types of plasmodia Phaneroplasmodium Conspicuous, often colored, with protoplasm forming veins with reversible streaming Aphanoplasmodium With a network of fine, transparent threads and homogenous protoplasm Protoplasmodium Microscopic, with homogenous protoplasm, giving rise to one sporophore Sporophores Consist of mass of spores formed inside peridium, spores intermingled with one of the following: Capillitium • threadlike, often ornamented Elaters • Threadlike, ornamented, not connected at ends Pseudocapillitium • Threads, bristles, membrane or platelike network Lime may be present on peridium, stalk, columella or capillitium, or nodes of pseudocapillitum 7 Sporocarp—stalked or sessile Capillitium (top left; photo by David Geiser) Pseudocapillium (top right; photo from Fifth Kingdom) Elaters (bottom left) May have columella Æ www.botany.hawaii.edu/.../Bot201/ Myxomycota/elaters.jpg Aethalium Large, cushionshaped sporophore, one per plasmodium Pseudoaethalium Cluster of sporophores grouped tightly together Photo by David Geiser Plasmodiocarp Sporophore developing along veins of a phaneroplasmodium; takes on reticulate shape of veins Photo by Stephen Sharnoff 8 Liceales-- Pale or brown spores, capillitium and lime absent, pseudocapillitium may be present Trichiales--Pale spores (yellow, orange or red) and abundant, conspicuous capillitium Dictydium Lycogala Photo by Stephen Sharnoff Physarales--Purplish-brown spores, usually with abundant and conspicuous lime on or in sporophore Badhamia Leocarpus Trichia Arcyria Stemonitales--Violet-brown spores, lime absent Lamproderma Diachea Fuligo Ceratiomyxales--Exosporous sporophores; probably belongs in protostelids (one genus, Ceratiomyxa) Photo by Stephen Sharnoff Photo by David Geiser Photo by Stephen Sharnoff Stemonitis 9 Protostelids Simplest known slime molds First discovered in 1970 Easily mistaken for sporulating structures of mucoraceous fungi or deuteromycetes Found in dead, attached plant parts, herbivore dung or soil and feed on bacteria, yeast and fungal spores 14 genera and 32 species Life cycle of simple protostelid http://comp.uark.edu/~fspiegel/protist.html#sporocarp%20morphology Protostelid Life Cycle Amoeboid tropic cells with filose pseudopodia round up to become one or more prespore cells that rise at the tip of a stalk during culmination and encysts to form one to four spores at apex of delicate stalk in simple life cycle Plasmodium and flagellated cells may be present in complex life cycles Sexual reproduction not known Life cycle of complex protostelid http://comp.uark.edu/~fspiegel/protist.html#sporocarp%20morphology 10
