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Slime mold

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== Ecology ==
== Ecology ==
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[[Image:TubiferaFerruginosa.jpg|thumb|150px|left|This slime mold, ''Tubifera ferruginosa'', eats decaying matter on a rotting log and has moved to the top of the log to reproduce]]
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[[Image:TubiferaFerruginosa.jpg|thumb|200px|left|This slime mold, ''Tubifera ferruginosa'', eats decaying matter on a rotting log and has moved to the top of the log to reproduce]]
Slime molds live in dark, moist habitats where there is abundance of food. They eat bacteria, protozoans, yeasts, fungi, decaying organic materials, and other microorganisms [http://serendip.brynmawr.edu/biology/b103/f01/web1/blucher.html#3] [http://universe-review.ca/R10-18-slimemoulds.htm]. They are most often found in forests and lawns, under rotting logs and leaves [http://www.coopext.colostate.edu/TRA/PLANTS/index.html#http://www.colostate.edu/Dept/CoopExt/TRA/PLANTS/slime.html]. Cellular slime molds also live in moist soil or manure [http://www.cs.cuc.edu/~tfutcher/Slimemolds.html]. Both cellular and plasmodial slime molds move across their habitats using amoeboid movement, ingesting food by the process of [[phagocytosis]], a form of [[endocytosis]] [http://www.infoplease.com/ce6/sci/A0845543.html]. Slime molds may also use [[chemotaxis]], following the chemical gradient given off by their food sources, to find food [http://universe-review.ca/R10-18-slimemoulds.htm]. Chemotaxis is also used by cellular slime molds when they aggregate, following the chemical gradient of cAMP [http://zool33.uni-graz.at/schmickl/Self-organization/Group_behavior/Slime_mold_behavior/slime_mold_behavior.html].
Slime molds live in dark, moist habitats where there is abundance of food. They eat bacteria, protozoans, yeasts, fungi, decaying organic materials, and other microorganisms [http://serendip.brynmawr.edu/biology/b103/f01/web1/blucher.html#3] [http://universe-review.ca/R10-18-slimemoulds.htm]. They are most often found in forests and lawns, under rotting logs and leaves [http://www.coopext.colostate.edu/TRA/PLANTS/index.html#http://www.colostate.edu/Dept/CoopExt/TRA/PLANTS/slime.html]. Cellular slime molds also live in moist soil or manure [http://www.cs.cuc.edu/~tfutcher/Slimemolds.html]. Both cellular and plasmodial slime molds move across their habitats using amoeboid movement, ingesting food by the process of [[phagocytosis]], a form of [[endocytosis]] [http://www.infoplease.com/ce6/sci/A0845543.html]. Slime molds may also use [[chemotaxis]], following the chemical gradient given off by their food sources, to find food [http://universe-review.ca/R10-18-slimemoulds.htm]. Chemotaxis is also used by cellular slime molds when they aggregate, following the chemical gradient of cAMP [http://zool33.uni-graz.at/schmickl/Self-organization/Group_behavior/Slime_mold_behavior/slime_mold_behavior.html].

Revision as of 04:36, 4 March 2009

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Slime mold
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Scientific Classification
Classes
  • Myxomycota:

Myxomycetes

Protosteliomycetes

  • Acrasiomycota

Acrasiomycetes

Mycetozoa Haeckel.JPG
Haeckel's Kunstformen der Natur

Contents

Introduction

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Anatomy

This slime mold plasmodium is growing on a leaf.

Slime molds have characteristics belonging to both animals and fungi: their reproductive phase resembles that of fungi, but they move and ingest food like an animal. They were once classified as fungi, but now are commonly held to be members of Kingdom Protista, although some place them in their own separate kingdom [1].

Slime molds range in size from a few centimeters to a foot or more in diameter [2]. They come in a variety of colors, ranging from dark browns, blacks, and purples, to bright yellow, orange, or red, while others may be gray or white [3]. A few tropical species are even bioluminescent (glow in the dark) [4].

Slime molds can be divided into two groups: plasmodial or true slime molds (Myxomycetes) and cellular slime molds (Acrasiomycetes). Both groups have a motile phase when growth and ingestion of food occurs and an immotile reproductive phase, and they differ mainly in their motile phase. Plasmodial slime molds begin as gamete cells that are either flagellated or amoeboid that fuse together and form a zygote [5]. The zygote's nucleus divides, but no cell walls form, resulting in a single-celled, multinucleate plasmodium that grow as the organism feeds and the nuclei continue to divide [6]. The plasmodium moves in amoeboid fashion using cytoplasmic streaming in order to find favorable conditions and food, and may move several feet in a single day [7]. The plasmodium continues to feed as long as conditions are good, but when food runs short or its habitat becomes too dry, the plasmodium changes into a fruiting body, the next phase in its life cycle. It hardens and produces stalked sporangia that contain spores, often after moving to a drier or better-lit location [8]. The spores are released and will develop into gametes to begin the life cycle again [9].

When slime molds experience very harsh conditions such as extremely cold or dry weather, they may harden into a sclerotium that can live for several years and then return to a plasmodium when conditions are favorable [10].

Cellular slime molds differ from plasmodial slime molds in that they are single-celled amoebas with only one nucleus in their motile phase. They move about like the plasmodial slime molds, ingesting food until the supply runs out. When there is no more food, all the slime mold amoebas in an area congregate and form a pseudoplasmodium, which is their fruiting body. The pseudoplasmodium becomes a stalked sporangium that releases spores which will germinate and restart the life cycle [11].

Reproduction

a plasmodium forming sporangia
Individual cellular slime mold amoebas aggregating to form a multicellular "slug" for reproduction

Plasmodial slime molds reproduce sexually by releasing spores. Reproduction occurs during the immotile phase. In plasmodial slime molds, the plasmodium moves to a dry, well-lit area and hardens. It then produces frutifications in one of four forms. The most common form is the sporangium, which is usually stalked and ends in a capsule containing the spores [12]. Other forms are the aethelium, a flat mass of fused sporangia; the pseudoaethalium, where the sporangia are very close together; and the plasmodicarp, which appear branched or veined [13]. The base of the fruiting body is the hypothallus [14]. In sporangia, the spores are in a capsule at the end of a stalk, but other fruiting bodies do not have stalks. The portion of the stalk that extends into the peridium (the capsule containing the spores) is the columella [15]. Inside the peridium, spores are connected to the capillitium, a tiny, thread-like network the runs throughout the peridium [16]. The spores are released from the peridium and scattered by the wind or other factors. When one reaches a damp, cool environment, the spore absorbs water, the cellulose wall breaks open, and a single, naked cell emerges [17]. This cell, a gamete, may have a flagellum depending on the level of moisture (cells released into aquatic environments will be flagellated, while those in drier habitats will not have a flagellum) [18]. The gametes feed for a short time, then merge to form a zygote. Flagellated gametes join with other flagellated gametes, and amoeboid gametes fuse with other amoeboid gametes [19]. The zygote continues to feed and its nucleus divides as it grows into a plasmodium.

Cellular slime molds live as individual cells that join together to form the reproductive structure. They can reproduce sexually or asexually [20]. In asexual reproduction, the individual cells release cAMP, a signaling molecule, when they are starving [21]. As other slime mold cells cross the cAMP tracks made by the starving amoebas, they also begin to produce cAMP and move to the highest concentration of cAMP, where all the other amoebas have gone [22]. Once they have aggregated together, the amoebas fuse together into a "slug" called the pseudoplasmodium that moves around for a short time, eating and looking for a place to form the fruiting body [23]. Like the plasmodial slime mold, the pseudoplasmodium looks for a light, dry are to form the frutification, which is called a sorocarp and consists of a sorophore (the stalk) and a sorus (the cluster of spores) [24]. As many as 125,000 amoeboid cells may join together, each becoming a different part of the fruiting body [25]. Anterior cells become the base and stalk, while posterior cells become the spores, which will germinate and become the next generation of amoebas [26].

Cellular slime molds may also reproduce sexually. Two amoebas will fuse together and begin engulfing other amoebas, forming a macrocyst that divides through meiosis and mitosis to produce more amoebas [27].

Ecology

This slime mold, Tubifera ferruginosa, eats decaying matter on a rotting log and has moved to the top of the log to reproduce

Slime molds live in dark, moist habitats where there is abundance of food. They eat bacteria, protozoans, yeasts, fungi, decaying organic materials, and other microorganisms [28] [29]. They are most often found in forests and lawns, under rotting logs and leaves [30]. Cellular slime molds also live in moist soil or manure [31]. Both cellular and plasmodial slime molds move across their habitats using amoeboid movement, ingesting food by the process of phagocytosis, a form of endocytosis [32]. Slime molds may also use chemotaxis, following the chemical gradient given off by their food sources, to find food [33]. Chemotaxis is also used by cellular slime molds when they aggregate, following the chemical gradient of cAMP [34].

Slime molds are frequently found in moist areas of gardens, such as on bark or mulch. They may occasionally grow over garden plants as well [35]. Although they do not directly harm living, healthy plants, slime molds do use them for structural support, and a large plasmodium may block sunlight from a plant and prevent photosynthesis from occurring [36]. A few slime molds do cause disease in plants, such as cabbage clubroot disease, which is caused by Plasmodiophora brassicae, a plasmodial slime mold [37]. Gardeners can get rid of slime molds by raking or mowing, or by spraying forcefully with a garden hose (however, this may also cause the plasmodium to grow since they thrive in damp environments) [38]. If they are not damaging plants, slime molds may be allowed to disappear naturally (they will die off when the weather becomes drier) [39].

Slime molds are found in late summer and early fall [40] [41]. The reproductive phase is the one most often observed because the slime molds move to a better lit and thus more visible location to form their fruitifications. There are roughly 500 species of plasmodial slime molds and only about 50 species of cellular slime molds [42]. Most species of slime mold can be found all over the world, especially in forests and gardens [43].

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