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Mortierella tsukubaensis sp. nov. from Japan, with a key to the homothallic species
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Mycol. Res. 105 (4) : 506–509 (April 2001). Printed in the United Kingdom.
Mortierella tsukubaensis sp. nov. from Japan, with a key to the homothallic species
Tsuneo WATANABE1, Yoshio WATANABE2, Takuma FUKATSU3 and Ryuichiro KURANE3 " Bioconsortia Program Laboratory, National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, 1-1, Higashi, Tsukuba, Ibaraki 305–8566, Japan. # Central Research Laboratories, Mercian Corporation, 9-1, Johnan 4 Chome, Fujisawa, Kanagawa 251-0057, Japan. $ National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, 1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan. E-mail : tsuneowa!nibh.go.jp Received 17 August 2000 ; accepted 23 October 2000.
Mortierella tsukubaensis sp. nov., isolated from uncultivated soil at Tsukuba, Japan, is described and illustrated as a new homothallic species. Simple, large sporangiophores with terminal, many-spored sporangia, large chlamydospores and naked zygospores are characteristic of M. tsukubaensis. A key of the 13 known homothallic species is provided.
INTRODUCTION
RESULTS AND DISCUSSION
During studies on lignocellulose decomposing fungi, a species belonging to the genus Mortierella forming large unbranched sporangiophores, large chlamydospores and naked zygospores in cultures was isolated from uncultivated soil at Tsukuba, Japan. The morphological characteristics of this fungus are not found in any described species (Gams 1977) and it is thus described here as new.
One Mortierella isolate was obtained from uncultivated soil in the rhizosphere of Japanese red pine (Pine densiflora) and oak (Quercus acutissima) on the campus ground of AIST, Tsukuba, Japan. It is unique in forming large unbranched sporangiophores, large chlamydospores and naked zygospores in cultures and belongs to Mortierella section Simplex W. Gams (1977). Therefore, this species closely resembles M. alpina Peyronel 1913 (syn. M. renispora Dixon-Stewart (1932)), M. chlamydospora (Chesters) Plaa$ ts-Nit. 1976 (Chien, Kuhlman & Gams 1974, Plaa$ ts-Niterink et al. 1976, Watanabe 1990), M. cogitans Degawa (Degawa & Tokumasu 1998b), M. epigama W. Gams & Domsch (Gams, Chien & Domsch 1972), M. kuhlmanii W. Gams 1976 (Gams et al. 1972, Kuhlman 1972 (as M. elongata Linnem. 1941)), and M. microzygospora Degawa (Degawa & Tokumasu 1998b) all of which form naked zygospores, but it differs from these in forming smooth chlamydospores and simple sporangiophores.
MATERIALS AND METHODS The fungus was isolated by the bait method with commercial toothpicks (Betula sp., 6n5 cm long). The autoclaved toothpicks were stood vertically, burying up to 4n5 cm deep in soil (nearly 30 g soil\100 ml glass vial) for 30 d. Subsequently the toothpicks were removed from the soil, washed under running tap water for at least 30 min, air-dried and placed on 7 ml water agar plates (two toothpicks\plate). After incubation at 25 mC for more than one d, single-hyphal tips were isolated as pure cultures. Living cultures were deposited at the Bioconsortia Program Laboratory, National Institute of Bioscience and HumanTechnology (NIBH), Agency of Industrial Science and Technology (AIST), Ministry of International Trade and Industry, and the Gene Bank, National Institute of Biological Resources, Ministry of Agriculture, Forestry and Fisheries (MAFF) in Tsukuba, the Central Research Laboratories, Mercian Corp., Fujisawa, Kanagawa (Mer, CRL), and the American Type Culture Collection (ATCC).
Mortierella tsukubaensis Ts. Watanabe, sp. nov. (Figs 1–17) Etym. : From the name of Tsukuba city, referring to the type locality. Coloniae in agaro decocto tuberosum pallide luteo-brunneae, dense et inconspicue lobulatae, mycelio aerio absente. Sporangiophora erecta, simplicia, hyalina, 600–2800 µm alta, 3–10 µm lata ad apices, 6–40 µm lata ad basim. Sporangia, globosa, hyalina, multispora, 25–50 µm diam ; dilapsa columellam minutam et collar inconspicuum relinquunt. Sporangiosporae hyalinae, ellipsoideae, subglobosae,
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Figs 1–10. Mortierella tsukubaensis. Fig. 1. Six-day-old colony on PDA at 25 mC in 9 cm plastic Petri dish. Fig. 2. Variously-sized chlamydospores and hyphae. Fig. 3. Upper portion of simple sporangiophore with intact sporangium. Fig. 4. Part of sporangiophore with minute columellae, rather conspicuous collarette and sporangiospores. Figs 5–6. Basal portions of common sporangiophore without vesicles (5) and rarely-formed sporangiophore with empty vesicles (6). Fig. 7. Fused young gametangia. Fig. 8. Immature zygospore with monoclinous major and minor suspensors. Figs 9–10. Mature zygospores with major suspensors, and a slightly inflated (9) or undiscernible or aborted minor suspensors (10). Bars l 20 µm in Figs 2–4, 7–10 ; 40 µm in Figs 5–6.
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Figs 11–17. Mortierella tsukubaensis. Fig. 11. Sporangiophore. Fig. 12. Sporangiospores. Fig. 13. Apices of sporangiophores with minute columellae and collarette. Fig. 14. Sporangiophore bases. Fig. 15. Intercalary and terminal chlamydospores. Fig. 16. Immature globose zygospores, and globose or subellipsoidal major suspensors and slightly swollen minor suspensors on the same hyphae (monoclinous, above) or different hyphae (diclinous, below). Fig. 17. Mature thick-walled zygospore with a major suspensor. Bars l 40 µm in Fig. 11 ; 10 µm in Figs 12–13 ; 20 µm in Figs 14–17.
4–10i4–7 µm. Zygospora globosae, leves, 34–52 µm diam ; suspensoribus hyalinibus, inaequales, 18–52i14–38 µm ; homothallica. Chlamydosporae globosae, solitariae, intercalares vel terminales, 10–54 µm diam. Typus : Colonia exsiccata : Japonia : Ibaraki, Tsukuba, isolata ex solo, 24 Mar. 1998, T. Watanabe TW98-120 (NIBH 98120-holotypus). Cultura viva : MAFF 237778, MER 98120 et ATCC 204319.
Colonies on potato-dextrose agar (PDA) after incubation for 5 d at 25 C 28–31 mm diam, white to pale yellow, delicately and densely lobed, aerial hyphae absent ; reverse pale yellow ; garlic odour absent. Sporangiophores erect, hyaline, simple, gradually tapering toward apex, mostly 600–2800 µm high, 6–40 µm wide at base, 2–10 µm wide near the apex, bearing a terminal sporangium, leaving a minute columella usually 5–7 µm wide, 4 µm high, and with a conspicuous collarette on dehiscence, arising from the vegetative mycelium or rarely appearing to be rhizoidal, surrounded with empty vesicles, mostly 20–30 µm wide. Sporangia hyaline, usually 25–50 µm diam. Sporangiospores hyaline, mostly ellipsoid, subglobose, or angular, 4–10i4–7 µm. Chlamydospores globose or sub-
globose, pale brown, usually intercalary, occasionally terminal, protoplasm dense, often granulate, variable in size, 10–54 µm diam. Zygospores formed in mycelial cultures originated from single hyphal tip (homothallic), superficial, unadorned, mostly 34–52 µm diam, double-walled, wall 1–1n5 µm thick, with unequal suspensors, major suspensors globose, ovate, ellipsoidal, or clavate, nearly equal to the zygospore in size, 18–52i14–38 µm, minor suspensors globose, subglobose, or cylindrical, slightly swollen hypha-like, curved, not well differentiated from vegetative hyphae, often aborted, mostly 10–18i5–7 µm. This fungus grew on several conventional agar media tested including Difco corn meal agar, Difco malt agar, halfstrength Difco oat meal agar, Difco YM agar, soil extractglucose-yeast extract agar (SGYA), and potato carrot agar (PCA). The last two media were prepared following medium formulations of The American Type Culture Collection (Jong et al. 1996). These cultures were similar to a PDA colony, although mycelia were thin and sparse on PCA and SGYA. Sporulation was best on PCA under laboratory conditions from 20 m to 26 m as compared with other cultures at 10 m, 20 m, or 25 m 12 d after inoculation. PCA is recommended for zygospore formation by Gams et al. (1972). Zygospores were often formed buried in rich agar media (PDA, MA, PCA, SGYA), or found in water agar with inocula from PDA or other rich agar medium cultures. Various stages of zygospore formation were observed on these media including fused young gametangia, immature zygospores, and unequal suspensors of monoclinous or diclinous origin (Figs 8, 16). At least 26 species of Mortierella have been reported to produce zygospores, including 12 homothallic species. The homothallic species include : M. alpina (heterothallim was noted by Kuhlman (1975), but M. renispora, a synonym of this species (Gams 1977) is regarded as homothallic (DixonStewart 1932) and it may, therefore, include both homothallic and heterothallic strains), M. chlamydospora (Chien et al. 1974, Plaa$ ts-Niterink et al. 1976, Watanabe 1990), M. cogitans (Degawa & Tokumasu 1998b), M. epigama (Gams et al. 1972), M. gemmifera M. Ellis (1940), M. kuhlmanii (as M. elongata) (Gams et al. 1972, Kuhlman 1972), M. microzygospora (Degawa & Tokumasu 1998b), M. nigrescens Tiegh. 1878 (Kuhlman 1972, Zycha 1935), M. polycephala Coem. 1863 (Dauphin 1908, Kuhlman 1872, Zycha 1935), M. rostafinskii Bref. 1881 (Kuhlman & Hodges 1972), M. stylospora Dixon-Stew. (1932), and M. turficola Y. Ling 1930 (Gams & Hooghiemstra 1976). Four of these species, M. gemmifera, M. nigrescens, M. polycephala and M. rostafinskii, form zygospores surrounded to varying extent by investing hyphae, and the remaining six (M. alpina, M. chlamydospora, M. cognitans, M. epigama, M. kuhlmanii and M. microzygospora), form naked zygospores. In two species, viz M. stylospora and M. turficola, mature zygospores have not been observed (Dixon-Stewart 1932, Gams & Hooghiemstra 1976). Although the information on the zygosporangial apparatus of M. rostafinskii is inadequate, and zygospore formation in several other homothallic species has not been observed again or confirmed (Ansell & Young 1988, Degawa & Tokumasu 1998b), M. tsukubaensis is differentiated from known homothallic species by the following key :
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Key to homothallic species of Mortierella 1.
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4(3) Chlamydospores spiny, sporangiospores not formed, zygospores naked . . . . . . . Chlamydospores spinulose, sporangiospores 10–12 µm diam, zygospores decorated with invested hyphae .
chlamydospora . polycephala
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. 6(5) Sporangiospores 300 µm tall, chlamydospores indistinct, small, zygospores naked . Sporangiospores 600 µm tall, chlamydospores large, to 54 µm diam, zygospores naked .
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. . alpina . tsukubaensis
7(5) Chlamydospores 30–50 µm diam, sporangiospores short ellipsoidal, 14–16i9–11 µm, zygospores naked, 100–150 µm diam . . . . . . . . . . . . . . . . . . . . . gemmifera Chlamydospores to 22 µm diam, sporangiospores elongate-ellipsoidal, 8–17i4–7 µm, zygospores naked, 50–60 µm diam . . . . . . . . . . . . . . . . . . . . . kuhlmanii 8(1) Sporangiophores simple or mostly simple Sporangiophores branched . . .
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9(8) Sporangiophores 100–250 µm, sporangiospores 2n5–3 µm diam, mature zygospores not yet observed . Sporangiophores 1000 µm tall . . . . . . . . . . . . .
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. turficola . . 10
10(9) Sporangiophores rhizoidal, sporangiospores oval to cylindrical, 5–7i3–4 µm, zygospores decorated with invested hyphae, over 125 µm diam . . . . . . . . . . . . . . . . . . rostafinskii Sporangiophores without rhizoid . . . . . . . . . . . . . . . . . 11 . . . nigrescens 11(10) Sporangiophore base to 50 µm wide, zygospores decorated with investing hyphae, 100–125 µm Sporangiophore base 10–13 µm wide, zygospores naked, with numerous depressions in the wall, about 20 µm diam . . . . . . . . . . . . . . . . . . . . microzygospora 12(8) Sporangiophores mesotonously branched, sporangia apophysate, sporangiospores broadly globose, 23–29i20–25n5 µm, zygospores naked, with polygonal ornamentation, about 70 µm diam . . . . . . . . . cogitans Sporangiophores basitonously branched, sporangia non-apophysate, sporangiospores fusoid, 9–14i3–6 µm, zygospores naked, thin-walled, 30–50 µm diam . . . . . . . . . . . . . . . . epigama
A C K N O W L E D G E M E N TS Financial support of this study by Bioconsortia Program, New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged as a part of the Project ‘ Development of technology of Bioconsortia and utilization of biological resources ’ of the Industrial Science and Technology, Agency of Industrial Science and Technology, Ministry of International Trade and Industry of Japan.
REFERENCES Ansell, P. J. & Young, T. W. K. (1988) The zygospore of Mortierella indohii. Transactions of the British Mycological Society 91 : 221–226. Chien, C.-Y., Kuhlman, E. G. & Gams, W. (1974) Zygospores in two Mortierella species with ‘ stylospores ’. Mycologia 66 : 114–121. Dauphin, M. J. (1908) Contribution a' l’ e! tude des MortieT relleT es. Annales des Sciences Naturelles, Botanique SeT rie 9 8 : 1–112. Degawa, Y. & Tokumasu, S. (1997) Zygospore formation in Mortierella capitata. Mycoscience 38 : 387–394. Degawa, Y. & Tokumasu, S. (1998a) Zygospore formation in Mortierella umbellata. Mycological Research 102 : 593–598. Degawa, Y. & Tokumasu, S. (1998b) Two new homothallic species of Mortierella, M. cogitans, and M. microzygospora, and their zygospore formation. Mycologia 90 : 1040–1046. Dixon-Stewart, D. (1932) Species of Mortierella isolated from soil. Transactions of the British Mycological Society 17 : 208–220.
Ellis, M. B. (1940) Some fungi isolated from pinewood soil. Transactions of the British Mycological Society 24 : 87–97. Gams, W. (1977) A key to the species Mortierella. Persoonia 9 : 381–391. Gams, W., Chien, C.-Y. & Domsch, K. H. (1972) Zygospore formation by the heterothallic Mortierella elongata and a related homothallic species, M. epigama sp. nov. Transactions of the British Mycological Society 58 : 5–13. Gams, W. & Hooghiemstra, H. (1976) Mortierella turficola Ling Yong. Persoonia 9 : 141–144. Jong, S. C., Dugan, F. & Edwards, M. J. (eds) (1996) ATCC Filamentous Fungi. 19th edn. American Type Culture Collection, Rockville, MD. Kulhman, E. G. (1972) Variation in zygospore formation among species of Mortierella. Mycologia 64 : 325–341. Kuhlman, E. G. (1975) Zygospore formation in Mortierella alpina and M. spinosa. Mycologia 67 : 678–681. Kuhlman, E. G. & Hodges, C. S. jr (1972) Rediscovery of Mortierella rostafinskii and Mortierella strangulata. Mycologia 64 : 92–98. van der Plaa$ ts-Niterink, A. J., Samson, R. A., Stalpers, J. A. & Weijman, A. C. M. (1976) Some oomycetes and zygomycetes with asexual echinulate reproductive structures. Persoonia 9 : 85–93. Watanabe, T. (1990) Zygospore induction in Mortierella chlamydospora by the soaking-plain-water-agar-culture method. Mycologia 82 : 278–282. Zycha, H. (1935) Mucorineae. Kryptogamenflora der Mark Brandenburg 6a(3) : 1–264. Corresponding Editor : P. M. Kirk
Mycol. Res. 105 (4) : 506–509 (April 2001). Printed in the United Kingdom.
Mortierella tsukubaensis sp. nov. from Japan, with a key to the homothallic species
Tsuneo WATANABE1, Yoshio WATANABE2, Takuma FUKATSU3 and Ryuichiro KURANE3 " Bioconsortia Program Laboratory, National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, 1-1, Higashi, Tsukuba, Ibaraki 305–8566, Japan. # Central Research Laboratories, Mercian Corporation, 9-1, Johnan 4 Chome, Fujisawa, Kanagawa 251-0057, Japan. $ National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, 1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan. E-mail : tsuneowa!nibh.go.jp Received 17 August 2000 ; accepted 23 October 2000.
Mortierella tsukubaensis sp. nov., isolated from uncultivated soil at Tsukuba, Japan, is described and illustrated as a new homothallic species. Simple, large sporangiophores with terminal, many-spored sporangia, large chlamydospores and naked zygospores are characteristic of M. tsukubaensis. A key of the 13 known homothallic species is provided.
INTRODUCTION
RESULTS AND DISCUSSION
During studies on lignocellulose decomposing fungi, a species belonging to the genus Mortierella forming large unbranched sporangiophores, large chlamydospores and naked zygospores in cultures was isolated from uncultivated soil at Tsukuba, Japan. The morphological characteristics of this fungus are not found in any described species (Gams 1977) and it is thus described here as new.
One Mortierella isolate was obtained from uncultivated soil in the rhizosphere of Japanese red pine (Pine densiflora) and oak (Quercus acutissima) on the campus ground of AIST, Tsukuba, Japan. It is unique in forming large unbranched sporangiophores, large chlamydospores and naked zygospores in cultures and belongs to Mortierella section Simplex W. Gams (1977). Therefore, this species closely resembles M. alpina Peyronel 1913 (syn. M. renispora Dixon-Stewart (1932)), M. chlamydospora (Chesters) Plaa$ ts-Nit. 1976 (Chien, Kuhlman & Gams 1974, Plaa$ ts-Niterink et al. 1976, Watanabe 1990), M. cogitans Degawa (Degawa & Tokumasu 1998b), M. epigama W. Gams & Domsch (Gams, Chien & Domsch 1972), M. kuhlmanii W. Gams 1976 (Gams et al. 1972, Kuhlman 1972 (as M. elongata Linnem. 1941)), and M. microzygospora Degawa (Degawa & Tokumasu 1998b) all of which form naked zygospores, but it differs from these in forming smooth chlamydospores and simple sporangiophores.
MATERIALS AND METHODS The fungus was isolated by the bait method with commercial toothpicks (Betula sp., 6n5 cm long). The autoclaved toothpicks were stood vertically, burying up to 4n5 cm deep in soil (nearly 30 g soil\100 ml glass vial) for 30 d. Subsequently the toothpicks were removed from the soil, washed under running tap water for at least 30 min, air-dried and placed on 7 ml water agar plates (two toothpicks\plate). After incubation at 25 mC for more than one d, single-hyphal tips were isolated as pure cultures. Living cultures were deposited at the Bioconsortia Program Laboratory, National Institute of Bioscience and HumanTechnology (NIBH), Agency of Industrial Science and Technology (AIST), Ministry of International Trade and Industry, and the Gene Bank, National Institute of Biological Resources, Ministry of Agriculture, Forestry and Fisheries (MAFF) in Tsukuba, the Central Research Laboratories, Mercian Corp., Fujisawa, Kanagawa (Mer, CRL), and the American Type Culture Collection (ATCC).
Mortierella tsukubaensis Ts. Watanabe, sp. nov. (Figs 1–17) Etym. : From the name of Tsukuba city, referring to the type locality. Coloniae in agaro decocto tuberosum pallide luteo-brunneae, dense et inconspicue lobulatae, mycelio aerio absente. Sporangiophora erecta, simplicia, hyalina, 600–2800 µm alta, 3–10 µm lata ad apices, 6–40 µm lata ad basim. Sporangia, globosa, hyalina, multispora, 25–50 µm diam ; dilapsa columellam minutam et collar inconspicuum relinquunt. Sporangiosporae hyalinae, ellipsoideae, subglobosae,
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Figs 1–10. Mortierella tsukubaensis. Fig. 1. Six-day-old colony on PDA at 25 mC in 9 cm plastic Petri dish. Fig. 2. Variously-sized chlamydospores and hyphae. Fig. 3. Upper portion of simple sporangiophore with intact sporangium. Fig. 4. Part of sporangiophore with minute columellae, rather conspicuous collarette and sporangiospores. Figs 5–6. Basal portions of common sporangiophore without vesicles (5) and rarely-formed sporangiophore with empty vesicles (6). Fig. 7. Fused young gametangia. Fig. 8. Immature zygospore with monoclinous major and minor suspensors. Figs 9–10. Mature zygospores with major suspensors, and a slightly inflated (9) or undiscernible or aborted minor suspensors (10). Bars l 20 µm in Figs 2–4, 7–10 ; 40 µm in Figs 5–6.
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Figs 11–17. Mortierella tsukubaensis. Fig. 11. Sporangiophore. Fig. 12. Sporangiospores. Fig. 13. Apices of sporangiophores with minute columellae and collarette. Fig. 14. Sporangiophore bases. Fig. 15. Intercalary and terminal chlamydospores. Fig. 16. Immature globose zygospores, and globose or subellipsoidal major suspensors and slightly swollen minor suspensors on the same hyphae (monoclinous, above) or different hyphae (diclinous, below). Fig. 17. Mature thick-walled zygospore with a major suspensor. Bars l 40 µm in Fig. 11 ; 10 µm in Figs 12–13 ; 20 µm in Figs 14–17.
4–10i4–7 µm. Zygospora globosae, leves, 34–52 µm diam ; suspensoribus hyalinibus, inaequales, 18–52i14–38 µm ; homothallica. Chlamydosporae globosae, solitariae, intercalares vel terminales, 10–54 µm diam. Typus : Colonia exsiccata : Japonia : Ibaraki, Tsukuba, isolata ex solo, 24 Mar. 1998, T. Watanabe TW98-120 (NIBH 98120-holotypus). Cultura viva : MAFF 237778, MER 98120 et ATCC 204319.
Colonies on potato-dextrose agar (PDA) after incubation for 5 d at 25 C 28–31 mm diam, white to pale yellow, delicately and densely lobed, aerial hyphae absent ; reverse pale yellow ; garlic odour absent. Sporangiophores erect, hyaline, simple, gradually tapering toward apex, mostly 600–2800 µm high, 6–40 µm wide at base, 2–10 µm wide near the apex, bearing a terminal sporangium, leaving a minute columella usually 5–7 µm wide, 4 µm high, and with a conspicuous collarette on dehiscence, arising from the vegetative mycelium or rarely appearing to be rhizoidal, surrounded with empty vesicles, mostly 20–30 µm wide. Sporangia hyaline, usually 25–50 µm diam. Sporangiospores hyaline, mostly ellipsoid, subglobose, or angular, 4–10i4–7 µm. Chlamydospores globose or sub-
globose, pale brown, usually intercalary, occasionally terminal, protoplasm dense, often granulate, variable in size, 10–54 µm diam. Zygospores formed in mycelial cultures originated from single hyphal tip (homothallic), superficial, unadorned, mostly 34–52 µm diam, double-walled, wall 1–1n5 µm thick, with unequal suspensors, major suspensors globose, ovate, ellipsoidal, or clavate, nearly equal to the zygospore in size, 18–52i14–38 µm, minor suspensors globose, subglobose, or cylindrical, slightly swollen hypha-like, curved, not well differentiated from vegetative hyphae, often aborted, mostly 10–18i5–7 µm. This fungus grew on several conventional agar media tested including Difco corn meal agar, Difco malt agar, halfstrength Difco oat meal agar, Difco YM agar, soil extractglucose-yeast extract agar (SGYA), and potato carrot agar (PCA). The last two media were prepared following medium formulations of The American Type Culture Collection (Jong et al. 1996). These cultures were similar to a PDA colony, although mycelia were thin and sparse on PCA and SGYA. Sporulation was best on PCA under laboratory conditions from 20 m to 26 m as compared with other cultures at 10 m, 20 m, or 25 m 12 d after inoculation. PCA is recommended for zygospore formation by Gams et al. (1972). Zygospores were often formed buried in rich agar media (PDA, MA, PCA, SGYA), or found in water agar with inocula from PDA or other rich agar medium cultures. Various stages of zygospore formation were observed on these media including fused young gametangia, immature zygospores, and unequal suspensors of monoclinous or diclinous origin (Figs 8, 16). At least 26 species of Mortierella have been reported to produce zygospores, including 12 homothallic species. The homothallic species include : M. alpina (heterothallim was noted by Kuhlman (1975), but M. renispora, a synonym of this species (Gams 1977) is regarded as homothallic (DixonStewart 1932) and it may, therefore, include both homothallic and heterothallic strains), M. chlamydospora (Chien et al. 1974, Plaa$ ts-Niterink et al. 1976, Watanabe 1990), M. cogitans (Degawa & Tokumasu 1998b), M. epigama (Gams et al. 1972), M. gemmifera M. Ellis (1940), M. kuhlmanii (as M. elongata) (Gams et al. 1972, Kuhlman 1972), M. microzygospora (Degawa & Tokumasu 1998b), M. nigrescens Tiegh. 1878 (Kuhlman 1972, Zycha 1935), M. polycephala Coem. 1863 (Dauphin 1908, Kuhlman 1872, Zycha 1935), M. rostafinskii Bref. 1881 (Kuhlman & Hodges 1972), M. stylospora Dixon-Stew. (1932), and M. turficola Y. Ling 1930 (Gams & Hooghiemstra 1976). Four of these species, M. gemmifera, M. nigrescens, M. polycephala and M. rostafinskii, form zygospores surrounded to varying extent by investing hyphae, and the remaining six (M. alpina, M. chlamydospora, M. cognitans, M. epigama, M. kuhlmanii and M. microzygospora), form naked zygospores. In two species, viz M. stylospora and M. turficola, mature zygospores have not been observed (Dixon-Stewart 1932, Gams & Hooghiemstra 1976). Although the information on the zygosporangial apparatus of M. rostafinskii is inadequate, and zygospore formation in several other homothallic species has not been observed again or confirmed (Ansell & Young 1988, Degawa & Tokumasu 1998b), M. tsukubaensis is differentiated from known homothallic species by the following key :
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Key to homothallic species of Mortierella 1.
Chlamydospores present Chlamydospores absent
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2 8
2(1) Chlamydospores reticulate, spiny or spinulose Chlamydospores smooth . . . .
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3 5
3(2) Chlamydospores reticulate, sporangiospores not formed, mature zygospores not observed . Chlamydospores spiny or spinulose . . . . . . . . . .
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stylospora . . 4
4(3) Chlamydospores spiny, sporangiospores not formed, zygospores naked . . . . . . . Chlamydospores spinulose, sporangiospores 10–12 µm diam, zygospores decorated with invested hyphae .
chlamydospora . polycephala
5(2) Sporangiophores simple . Sporangiophores branched .
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6 7
. 6(5) Sporangiospores 300 µm tall, chlamydospores indistinct, small, zygospores naked . Sporangiospores 600 µm tall, chlamydospores large, to 54 µm diam, zygospores naked .
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. . alpina . tsukubaensis
7(5) Chlamydospores 30–50 µm diam, sporangiospores short ellipsoidal, 14–16i9–11 µm, zygospores naked, 100–150 µm diam . . . . . . . . . . . . . . . . . . . . . gemmifera Chlamydospores to 22 µm diam, sporangiospores elongate-ellipsoidal, 8–17i4–7 µm, zygospores naked, 50–60 µm diam . . . . . . . . . . . . . . . . . . . . . kuhlmanii 8(1) Sporangiophores simple or mostly simple Sporangiophores branched . . .
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. 9 . 12
9(8) Sporangiophores 100–250 µm, sporangiospores 2n5–3 µm diam, mature zygospores not yet observed . Sporangiophores 1000 µm tall . . . . . . . . . . . . .
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. turficola . . 10
10(9) Sporangiophores rhizoidal, sporangiospores oval to cylindrical, 5–7i3–4 µm, zygospores decorated with invested hyphae, over 125 µm diam . . . . . . . . . . . . . . . . . . rostafinskii Sporangiophores without rhizoid . . . . . . . . . . . . . . . . . 11 . . . nigrescens 11(10) Sporangiophore base to 50 µm wide, zygospores decorated with investing hyphae, 100–125 µm Sporangiophore base 10–13 µm wide, zygospores naked, with numerous depressions in the wall, about 20 µm diam . . . . . . . . . . . . . . . . . . . . microzygospora 12(8) Sporangiophores mesotonously branched, sporangia apophysate, sporangiospores broadly globose, 23–29i20–25n5 µm, zygospores naked, with polygonal ornamentation, about 70 µm diam . . . . . . . . . cogitans Sporangiophores basitonously branched, sporangia non-apophysate, sporangiospores fusoid, 9–14i3–6 µm, zygospores naked, thin-walled, 30–50 µm diam . . . . . . . . . . . . . . . . epigama
A C K N O W L E D G E M E N TS Financial support of this study by Bioconsortia Program, New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged as a part of the Project ‘ Development of technology of Bioconsortia and utilization of biological resources ’ of the Industrial Science and Technology, Agency of Industrial Science and Technology, Ministry of International Trade and Industry of Japan.
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