Bull. Natn. Sci . Mus. , Tokyo, Ser. B, 24(3 ), pp. 81 - 84, September 22 , 1998

Dictyostelids in Japan XI. Dictyostelium giganteum SinghHiromitsu Hagiwara
Department of Botany, National Science Museum,4- 1- 1 Amakubo, Tsukuba, lbaraki , 305- 0005 Japan

Abstract Dictyostelium giganteum was obtained from forest soil samples collectedin Bonin Islands and Honshu. This may be the first report of this species in Japan .
Key words:
macrocyst.

cellular slime mold, dictyostelid, Dictyostelium giganteum , Japan,

In the course of my studies on Japanese dictyostelids, Dictyostelium giganteum
Singh was obtained from Bonin Islands and Honshu. This species had not been reported from Japan except for Hokkaido; it was described by Kanda and Yonezuka( 1979) as new to Japan based on the isolate H2 from lakeside soil , Kushiro-city.
Judging from the description made by them, however, I doubt that their isolate was D.
giganteum (Hagiwara, 1989). H2 had been already lost (Kanda, personal communication). Therefore, I will describe D. giganteum based on my isolates. Procedures ofisolation, cultivation and observation are the same as those reported previously(Hagiwara, 1989). Twenty spores per isolate are used for calculating the mean spore
diameter. Range of mean spore diameters of the isolates examined is indicated by
MD in the following description.
(Figs. I, 2)
Dictyostelium giganteum Singh, J. Gen. Microbial. I: 17 ( 194 7).
=Dictyostelium magnum Hagiwara, Bull. Natn. Sci. Mus., Tokyo, Ser. B. 9: 155(1983).
When cultured at 20°C on non-nutrient agar with Escherichia coli, sorocarps
solitary (Fig. 2B), rarely branched; sorophores 2.1- 7.9mm in length, with simple,typically capitate but sometimes obtuse tips (Figs. I A, 2D- 2F), sometimes with supporting cells (pointed by arrows in Figs. I B & 2G), with supporters if prostrate (Fig.
2H), I 0--40 f..Lm in diam. at a level I 00 f..Lm above the bottom, 2- 6 f..Lm in diam. at alevel 50 f..Lm below the top; basal disks not well-deve loped (Fig. I B), 20- 77.5 f..Lm indiam.; sori white, (30- ) 60--450 f..Lm in diam. ; spores hyaline, oblong to ellipsoid, usually 1.7- 2. 1 times longer than broad, smooth, mostly 6.3- 8.0 X3.3--4.1 (MD 6.97.2 X3.6-3 .9)f..Lm, without polar granules (Fig. 2C); pseudoplasmodia with radiatestreams (Fig. 2A), - 16.5 mm in diam. , usually not migrating without sorophore formation, usually producing single sorogens.
Isolates examined: Oga3 , from forest soil , Ani-jima, Bonin Islands, Tokyo Pref. ,82

Hiromitsu Hagiwara

A

Fig. I. Dictyostelium giganteum. A. Sorophore tips. B. Sorophore bases. Note support ing cells
indicated by arrows. C. Sorophore base of a prostrate sorocarp. Scale= I 0.um.

10 March 1985 ; CSBl and CSB7, from forest soil, Boso-fudokinooka, Sakae-cho,lnba-gun, Chiba Pref. , 2 July 1996.
World distribution: Asia; India, Japan, Nepal , Oman, Pakistan, Taiwan. N.
America; Alaska to California. S. America; Uruguay. Europe; England, France,Germany, the Netherlands, Switzerland.
Dictyostelium giganteum is characterized by the very large white sorocarps, thesimple and capitate sorophores tips, and the short and thick spores without polargranules.
According to the terminology in Hagiwara ( 1989), Dictyostelium giganteum is a"gigantic" species, namely, its non-prostrate large sorophores usually exceeds 6 mmin length. Five gigantic species of Dictyostelium have been reported from Japan; D.
firmibasis Hagiwara, D. pseudo-brefeldianum Hagiwara, D. purpureum Olive, D. robustum Hagiwara and D. septentrionalis Cavender. Of them, D. firmibasis is the mostsimilar to D. giganteum in appearance of sorocarps under a di ssecting microscope,but it differs from D. giganteum in the slender spores, which are usually 2.0- 2.7
times longer than broad (Hagiwara, 1989). D. pseudo-brefeldianum is different fromD. giganteum macroscopically in the thin sorocarps and microscopically in theDictyostelids in Japan XJ. Dictyostelium giganteum Singh83

Fig. 2. Dictyoste/ium giganteum. A. Pseudoplasmodium. X24. B. Growth habit of a sorocarps.
Note that one sorocarp was produced from one pseudoplasmodium. X 24. C. Spores. X 1200.
D- F. Sorophore tips which are simple and typically capitate. X480. G. Supporting cells(arrow) surrounding a sorophore base. X480. H. Supporter. X480. I. Macrocysts made by thepair of a Japanese isolate CSB7 and the tester strain WS-589. X240.

clavate tips of sorophores. D. purpureum distinctly differs from D. giganteum in thepurple sorocarps. D. robustum are easily distinguishable from D. giganteum by thelarger sorocarps with very thick sorophores. D. septentrionalis may be not misidentified with D. giganteum by the thicker sorophores with well-developed basal disks,Hiromitsu Hagiwara

84

Table I. Macrocyst formation among pairs of Japanese isolates, tester strains and the type strainof Dictyostelium giganteum.
WS-588CSB ICSB7WS-589"Singh"++*+CSBI

CSB7+** Macrocyst formation was recognized but the macrocysts scored were less than I0 per plate.
and it is clearly distinct in the large spores.
Dictyostelium giganteum is heterothallic and requires the pairing of compatible
mating types to effect macrocyst formation (Erdos et al., 1975). As a result of themating tests of Japanese isolates pairing with the type strain "Singh" and two testerstrains, WS-588 (ATCC32961) and WS-589 (ATCC32962), three pairs made macrocysts; CSB 1 and WS-588, CSB7 and "Singh", and CSB7 and WS-589 (Table 1, Fig.
21). Oga3 was not tested for its subcultures had been lost.

Acknowledges
I thank Dr. Toyozo Sato of the National Shikoku Agricultural Experiment Station for collecting soil samples in Bonin Islands. Also thanks are due to Drs. J. C.
Cavender of the Ohio University and S.-C. Jong of the American Type Culture Collection for supplying subcultures of the type strain and two tester strains, respectively.

References
Erdos, G. W., K. B. Raper & L. K. Vogen, 1975. Sexuality in the cellular slime mold Dictyostelium
giganteum . Proc. Na tl. Acad. Sci. USA, 72 : 970- 973.
Hagiwara, H., 1989. The Taxonomic Study of Japanese Dictyostelid Cellular Slime Molds. 131 pp.
National Science Museum, Tokyo.
Kanda, F. & K. Yonezuka, 1979. A species of Dictyostelia isolated from lakeside soil of Harutoriko.
Kushirohakubutsukanpo , 258: 39-40. (In Japanese)