Peridium of the acellular slime moldFuligo septica: Structure and composition

EXPERIMENTAL

MYCOLOGY

6, 195-199(1982)

BRIEF NOTE Peridium CHARLES

of the Acellular P. CHAPMAN,

Department of Microbiology,

Slime Mold Fuiigo and Composition

septica:

Struct

RODNEY

K. NELSON,

Louisiana

State University, Baton Rouge, Louisiam

Accepted for publication

AND

MICHAEL

ORLQWS~ 70803

December 9, 1981

CHAPMAN, C.P., NELSON, R.K., AND ORLOWSKI, M. 1982. Peridium of the acellular slime mold Fuligo septica: Structure and composition, Experimental Mycology 6, 195-199. The peridium, an outer sheath surrounding the sporangium of acellular slime molds, was characterized for the first time in the species F&go septica. It is an intricately channeled bilaminar structure with a relatively thin outer face composed mainly of protein and carbohydrate and a thicker inner layer composed essentially of calcium carbonate and calcium oxalate. These calcium salts are present as porous sheets of closely packed spherical particles. INDEX DESCRIPTORS: slime molds; myxomycetes; mycetozoans; Fuligo septica; peridium.

The acellular slime molds are a large, diverse group of eukaryotic microorganisms classified as the myxomycetes (Martin and Alexopolous, 1969) or the mycetozoans (Olive, 1975). They have a complex life cycle with the production of several specialized cell types. These organisms grow vegetatively as an aseptate, multinucleate mass of protoplasm called a plasmodium. The plasmodium moves by amoeboid locomotion and subsists by phagocytizing other microbes. When conditions become unsuitable for further growth the plasmodium fructifies. The fruiting body may be quite elaborate (as in Physarum, Didymium, or Stemonitis, for example), possessing a base, a stalk, and an ornate sporangium containing a columella, capillitia, and many spores. Alternatively, it may be a very simple structure as in the genus F&go. In this simple but very large form it is called an aethalium. A thin, fragile outer layer called the peridium covers the sporangium or aethalium. Because of difficulty in collecting purified peridium in sufficient amounts from most species of * To whom reprint requests should be addressed.

myxomycetes very little is known about the composition of this structure. The aethalia of F&go septica permited collect enough pure peridium from this species to carry out an analysis of its trastructure and chemical compos~t~o~~ results of which are presented here. Aethalia were collected from and identified as previously describe lson and Orlowski, 1981). Figure la presents a cross section of a typical aethaiium of F. septica. The peridium is the thin light layer (arrow) at the surface of this strut neath the peridium is a thick layer of bl densely packed spores. Separ spores from the substratum is a colored layer, different in textu position from the peridium, hypothahus. The i r and outer faces o the peridium look stinctively differing under the light m ope. The outer face appears to be covered with a deeply p mented (yellow, brown, or gray) matrix a is much more cohesive than which is a light ivory color and re crumbles at the tout outer faces are penetr network of tunnels. 195 0147-5975182/020195-05$02.8018 Copyright AU righls

@ 1982 by Academic R-ess, Inc. of reproduction in any form reserved.

196

CHAPMAN,

NELSON,

AND

ORLOWSKI

1. (a) Light micrograph of a Fuligo septica aethalium in cross section. The specimen was FIG. observed through a Wild M7S stereomicroscope (bar = 1 mm). The top layer is the peridium (arrow), immediately under that is a dark layer of spores, and on the bottom of the fructification is the hypothallus. (b) Scanning electron micrograph of the outer face of the peridium (bar = 100 pm). (c) Higher magnification of structure in b (bar = 10 Km). (d) Scanning electron micrograph of the inner face of the peridium (bar = 250 pm). (e) Higher magnification of structure in d (bar = 5 pm). (f) Higher magnification of structure in e (bar = 1 pm). All peridial specimens were observed using a JEOL JEM-100CX electron microscope equipped with a high-resolution scanning device.

The fragile peridial crust was collected by gently brushing it from the surface of the aethahum with a camel’s hair brush or lifting it off with a pair of forceps. Care was taken to avoid picking up spores from the layer underneath the peridium. Figure lb presents a scanning electron micrograph of the outer face of the peridium. The labyrinth of tunnels in the structure is readily apparent. Figure lc shows the outer face at a higher magnification. The tunnel walls are relatively smooth

but with a fibrous grain to them. Figure Id presents a scanning electron micrograph of the inner face of the peridium. A network of tunnels is also observed here. These tunnel walls are angular rather than smooth and are thinner than the ones found on the surface. A higher magnification of the inner face shows a remarkable structure composed of billions of spherical particles in laminar sheets (Fig. le). The sheets appear to be approximately six to seven particles in thickness (Fig. 2) and are interspersed with

PERIDIUM

OF

F&go

septica

FIG. 2. End-on view of a Iaminar sheet of calcium carbonate-calcium peridium of Fuligo septica. Bar = 1 pm.

small pores. Further magnification of this material shows that the spherical particles are usually connected to their adjacent neighbors by narrow bridges (Fig. 14. Qualitative analyses for anions were performed as described by Belcher and Weisz (1956, 1958). Oxalate was additionally identified by the Pizzalato reaction with silver nitrate (Silver and Price, 1969). Carbonate was additionally identified by X-ray diffraction analysis of powdered peridium. Qualitative analysis of cations was performed by energy-dispersive X-ray spectroscopy of powdered peridium using an ISI-60A scanning electron microscope equipped with an EDAX Model 9100 System 60 spectrometer and by atomic absorption spectroscopy with a Perkin-Elmer Model 303 atomic absorption spectrophotometer. Carbonate was quantitated by titration with hydrochloric acid (Skoog and West, 1963). Oxalate was quantitated by titration with potassium permanganate (Skoog and

oxalate particles in the

West, 1963). Phosphate was measure ascorbate -molybdate reagent method of Chen et al. (1956). Tot quantitated by the assay (Herbert et ak., Total neutral sugar was measu the anthrone reagent (Herber 1971). Total amino sugar was d by the Elson- Morgan procedure et al., 1971). Calcium was quantita the atomic absorption spectrop All analytical experiments were on three to six different peridial The quantitative data presented resent the complete analysis of a specimen performed in replicat aged. Data from other specimen I: 10% of these values. The gross chemical composition peridium is presented in Table 1. was the only cation shown to exist nificant amounts, constituting >99% metallic elements present and 37% total dry weight of the

1971).

s

of t in sigof all caf the

198

CHAPMAN,

NELSON,

TABLE 1 Chemical Composition of Peridium from F&go septica Component

Percentage of dry weight

Carbonate Oxalate Phosphate Calcium Protein Total carbohydrate Amino sugars Neutral sugars Total components identified

40.0 15.6 0.1 37.0 6.8 3.8 2.9 0.9 103.3

AND

ORLOWSKI

When additional studies are done, it will prove interesting to see how the peridial compositions of other myxomycetes compare with that of F. septica. Based on the qualitative descriptions of “lime” distribution in the peridia of other slime molds (Martin and Alexopolous, 1969), F. septica may turn out to be an atypical case with regard to the amount and location of the calcium salts. The function of the thick layer of calcium salts is only speculative at this time. The spores within the aethalium are quite anhydrous (10% water by weight) and germinate only when exposed to water at low cell densities (Nelson and Orlowski, 1981). The calcium salts may regulate germination by affecting the pH or water activity of the immediate surroundings or by acting as an autoinhibitor until sufficiently diluted by ambient water. Alternatively, the calcium salts may have no specific function at all, but may simply be excreted during fructification as the spores discharge water.

nate, oxalate, and phosphate were the only anions detected, with the latter making only a trace contribution. The calcium carbonate was present in some specimens as crystalline calcite, displaying major X-ray diffraction peaks at lattice spacings of d = 3.03 A [l/I1 = 1001, 2.49 A [14], 2.28 A [18], 2.09 A [18], 1.91 A [17], and 1.87 A [17]. In other samples the calcium carbonate lacked a crystalline structure. The calcium oxalate also proved to be amorphous. These calcium salts constituted the bulk of the ACKNOWLEDGMENTS peridium. A significant amount of protein and carbohydrate were also present (Table We thank Drs. Thomas Shelton, David Wertz, and 1). The carbohydrate contained both neu- Luis Vidaurreta and Messrs. Roger Miller and Robert Harvey for their contributions to this work. This retral and amino sugars. search was supported in part by NIH Biomedical ReTreatment of the peridium with dilute search Grant 2SO7 RR07039-10 awarded to Louisiana acid (1 N HCl) dissolved away the inner State University and allocated to M. Orlowski by the layer but left intact the outer layer of this LSU Council on Research. structure. This remaining layer was composed entirely of protein and carbohydrate. REFERENCES Some specimens were observed to possess a peridium with distinct inner and outer BELCHER, R., AND WEISZ, H. 1956. Studies in qualitative inorganic analysis. II. A semi-systematic layers, physically separated and not scheme for the detection of anions. Mikrochim. Acta adhering to one another. In these speci1956: 1847- 185.5. mens the inner layer contained practically BELCHER, R., AND WEISZ, H. 1958. Studies in qualitano protein or carbohydrate, whereas the tive inorganic analysis. VIII. Notes on the semiouter layer was greatly enriched in these systematic scheme for the detection of anions. Mikrochim. Acta 1958: 571-576. substances. It is therefore probable that the H. peridium is composed of a relatively thin CHEN, P. S., JR., TORIBARA, T. Y., AND WARNER, 1956. Microdetermination of phosphorus. Anal. outer face of protein and carbohydrate covChem. 28: 1756-1758. ering a thicker inner layer of calcium car- HERBERT, D., PHIPPS, P. J., AND STRANGE, R. E. bonate and calcium oxalate. 1971. Chemical analysis of Microbial cells. In Merh-

PERIDIUM

OF

ads in Microbiology (J. R. Norris and D. W. Ribbons, Eds.), Vol. 5B, pp. 209-344, Academic Press, London/New York. MARTIN, G. W., AND ALEXOP~LOUS, C. J. 1969. The Myxomycetes. Univ. of Iowa Press, Iowa City. NELSON, R. K., AND ORLOWSKI, M. 1981. Spore germination and swarm cell morphogenesis in the acellular slime mold Fuligo septica. Arch. Microbial. 130: 189-194.

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OLIVE, L. S. 1975. The Mycetozoans. Academic Press, New York. SILVER, V. L., AND PRICE, 3. L. 1969. remonstration of calcium oxalate crystals in plant tissues by the Pizzolato (AgN03-H,O,)method. Stein Teciznol. 4% 257-259. SKOOG, D. A., AND WEST, D. hf. 1963. Fundameattals of Analytical Chemistry. Bolt, Rinehart & Winston, New York.