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What’s Bugging You—Slime Molds
By Kevin T. Smith, Ph.D. Plant Physiologist, USDA Forest Service
Summer rains in the northeastern US bring out fist-sized masses of grainy yel- low goo, frequently on wood chip mulch or decaying wood (Fig. 1). *e first con- cerned “what is that” phone call usu- ally is followed the next day by a more alarmed “ what is that ”, when the blob has moved a foot or two across the mulch. All too often, alarm moves to disgust when I put the common name of “dog vomit fungus” ( Fuligo septica is the scien- tific name) on the mass. *is is actually a great opportunity to learn about and enjoy a richly varied and beautiful part of our natural biodiversity.
Fuligo is a Myxomycete, literally “slime mold.” *e Fuligo stage we usually see is the plasmodium, essentially a single huge cell containing many nuclei. Slime molds are not fungi but they share their habi- tat with fungi and mycologists tradition- ally study them. Arborists are likely to mal disease. Unlike mycelial fungi which and all other life by the ability to move encounter slime molds and a little under- often extend their hyphae deeply into across surfaces, producing a relatively standing can enhance our relationship leaf litter or decomposing wood, slime large plasmodium with many nuclei with the landscape. Slime molds are not molds live on surfaces especially shaded, and no cell walls, and the digestion of harmful, they do not cause plant or ani- well-watered mulch and lawns. As a mat- food within their own bodies.
Figure 2: Life cycle ter of cosmetics, a blast from a garden hose or a sweep of a rake can break up A few decades ago, myxomycetes were the visible portion of a slime mold. How- classified in a separate kingdom, the Pro- ever, they are much more interesting tista, along with the protozoa. Biologists to observe than to remove! now recognize that protists or proto- zoa are not natural groups of organisms Slime molds show great and most specialists tend to avoid those variation in structure and catch-all terms for unrelated organisms. appearance and experts are still determining their rela- Although details vary among the approxi- tionships to each other and to mately 700 known species of slime molds, other organisms. *e plasmodial they tend to follow a common life cycle slime molds are distinct from fungi (Fig. 2). As with fungi, myxomyce-
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What’s Bugging You—Slime Molds continued
tes produce microscopic spores. Unlike fungi, the myxomycete spore germinates to release one of two kinds of cells. *e ASCA first is an amoeboid-type cell known as a myxamoeba. In a favorable environment, a myxamoeba can reproduce by cell divi- Consulting 2014 sion to form new and independent myx- amoebae (the plural for myxamoeba). Academy Under adverse conditions, a myxamoeba may rapidly form a thin-walled microcyst February 25–28, 2014 as a dormancy strategy and then revive Hyatt Regency Newport Beach Newport Beach, CA as conditions occur. When free water is available, a germinating spore produces the second type known as a swarm cell, Take Your Career usually with one long whiplash and one very short flagellum. *e myxamoeba and swarm cell, although di fferent struc- turally, are interconvertible, depending to the Next Level on environmental conditions.
When concentrations of myxamoebae or swarm cells reach some threshold Since its inception in 1995, more than 750 aspiring concentration, two cells fuse to form a consultants and Consulting Arborists have attended zygote. However, the slime mold cells ASCA’s Consulting Academy to learn and further are self-sterile and need to be from dif- hone the skills necessary to develop and maintain ferent genetic individuals for fusion. *e thriving consulting practices. movement of myxamoebae and swarm As the most comprehensive training experience cells facilitates the meeting of comple- for arborists who consult, the Consulting Academy mentary cells. *e zygote divides many includes interactive workshops and lectures on all times to form the large, multinucleate aspects of consulting arboriculture. Adding to the * experience is the benefit of networking with fellow plasmodium. is plasmodium is what Consulting Arborists as you share this intensive we first see as Fuligo moves across the three-day conference. lawn or wood chip mulch. As with myx- amoebae and microcysts, adverse envi- 3 Big Reasons to Attend ronmental pressure can induce small • You’ll be one step closer to becoming a Registered portions of plasmodium to form thick- Consulting Arborist® (RCA)—the industry’s most walled sclerotia. prestigious professional designation. • You’ll develop and hone the skills you need to stand Free-living myxamoebae and swarm cells apart from your competition—report writing, the role as well as the plasmodium gain their consultants can play in contentious situations, forensic nutrition by phagocytosis, the surround- investigations, guidelines for a professional consulting ing and engulfing of bacteria, small pro- practice and more. tozoa, or fragments of organic matter. • You’ll gain the necessary skills to transition to a *e spiral motion of the whiplash flagel- consulting career. lum of swarm cells may even force bac- teria and other food particles towards an Save the Date! ingestion site on the swarm cell surface. www.asca-consultants.org *is is critically di fferent from fungi which digest their food sources outside and bring the dissolved nutrients inside the fungal cells. Slime molds can also
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What’s Bugging You—Slime Molds continued
Figure 3: HemitrichiaPhysarum ported by very thin, dark stalks. I have seen these develop on wooden frame con- struction exposed to prolonged damp- ness. I find the fragile bristles of Cera- tiomyxa most often on dead logs in dark, shaded woodland plantings (Fig 6).
*e plasmodium and the fruit bodies of slime molds can be quite dramatic in appearance, yet most of the biological activity of slime molds in unseen. *e life cycle is well-established, but we don’t know the duration or proportion of bio- mass at each stage. We know that slime take up soluble nutrients from their envi- look like clumps of brown whiskers, 1-2 molds graze on living soil microorgan- ronment. Undigested material is forcibly cm tall (Fig. 5). Immature fruit bodies isms, but their contribution to the soil ejected from the myxamoeba. are brick-red to carmine cylinders sup- food web and plant nutrition is largely unknown. When I first noticed slime *e ability to move allows the plasmo- molds, they seemed rare and exotic. Now Figure 4: HemitrichiaPhysarum dium to find food and a suitable envi- I see them quite often and perhaps you ronment for growth and development. will too! As a group, the slime molds make Following the attainment of some thresh- a rich contribution to our landscape. old size and with some environmental cues, the plasmodium moves from a wet to a drier environment to form a sporan- Figure 5: Stemonitis gium or fruiting body. Shifts in metabo- lism convert the multinucleate mass of the plasmodium into uninucleate spores and a variety of of spore-containing spo- rangia, the size and shape of which are the usual basis for field identification and classification.
Another slime mold with a conspicuous plasmodium is Physarum polycephalum . *e Physarum plasmodium often occurs on the gills or pores of mushrooms (Fig. 3). Some experts suggest that spores and associated bacteria may provide a good Figure 6: Ceratiomyxa food source for the slime mold.
For most slime molds, the plasmodial stage is not readily noticed in nature, but the developing and mature fruitbodies can be quite dramatic. *e bright orange Hemitrichia visibly stands out from the supporting wood surface (Fig. 4). Developing fruitbodies are very soft and smear easily. As Hemitrichia fruit bod- ies mature, they become firm and mus- tard yellow in color. Mature Stemonitis
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