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Megalohypha, a new genus in the Jahnulales from aquatic habitats in the tropics

     Department of Plant Biology, University of Illinois, Room 265 Morrill Hall, 505 South Goodwin Avenue, Urbana, Illinois 61801

Somsak Sivichai

     BIOTEC-Mycology, National Center for Genetic Engineering and Biotechnology, 113 Thailand Science Park, Paholyothin Road, Klong 1, Klong Luang, Pathumthani, 12120 Thailand

Carol A. Shearer

     Department of Plant Biology, University of Illinois, Room 265 Morrill Hall, 505 South Goodwin Avenue, Urbana, Illinois 61801

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS TAXONOMY DISCUSSION LITERATURE CITED

 

A new fungus collected from submerged wood in tropical forest streams in Panama and Thailand is described as a new genus and species in the Jahnulales. This fungus, Megalohypha aqua-dulces, is described based on ascospore morphology, which differs substantially from that of the other genera in the Jahnulales. It has these morphological features: ascomata hyaline, translucent, with subtending, wide, brown, septate, stoloniferous hyphae; peridium of large, thin-walled cells; hamathecium of septate pseudoparaphyses; asci clavate, fissitunicate, 8-spored; and ascospores 1-septate, brown, rough-walled, with longitudinal sulcate striations. An interesting feature of Megalohypha aqua-dulces, which it shares with some other taxa in Jahnulales, is the presence of both sessile and stalked fruiting bodies. In addition, the stalks have morphology that consists of a wide hypha with a narrower hypha apparently enclosed within and the stalks are strongly constricted at the septa.

Key words: euascomycetes, freshwater, fungal systematics, submerged wood

	INTRODUCTION

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In our on-going inventory of freshwater filamentous euascomycetes, a new fungus with characteristics of the Jahnulales Pang, Abdel-Wahab, El-Sharouney, E.B.G. Jones & Sivichai was collected from streams in the tropical rain forests of Panama and from a stream in Thailand. The order Jahnulales was erected based on a well supported clade from molecular analyses and morphological characteristics (Pang et al 2002) that include stalked/sessile ascomata, hyphal stalk cells that are ca. 40 µm wide, and 2-celled ascospores with or without appendages or sheaths (Pang et al 2002). While our new fungus presents the diagnostic morphological characteristics of the Jahnulales (Pang et al 2002) it is distinctively different from other genera in this order. Therefore the fungus is described as a new genus and species in the Jahnulales.

	MATERIALS AND METHODS

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Samples of submerged, partially decomposed woody debris were collected from rivers and streams at Soberania National Park in lowland tropical forest in central Panama and Than Bok Khorani National Park in Thailand. Samples were placed in Ziploc^TM plastic bags containing paper towels and returned to the laboratory. Samples were incubated in the laboratory in plastic boxes containing moistened paper towels at ambient temperature (about 24 C) and examined with a dissecting microscope immediately after collection and periodically for 9 mo.

Ascomata were placed on a cover glass on a microscope slide in a drop of distilled water and opened with dissecting needles to release asci and ascospores. Aqueous nigrosin or India ink was added to the water mounts to reveal appendages or gelatinous sheaths on the ascospores. Distilled water was replaced with glycerin for preservation using the double cover glass method (Volkmann-Kohlmeyer and Kohlmeyer 1996). Additional ascomata were fixed and sectioned with a modification of the technique outlined by Huhndorf (Huhndorf 1991, Fallah and Shearer 2001). Digital images were obtained with a Spot RT digital camera using an Olympus microscope equipped with Nomarski interference optics. Images were processed with Adobe Photoshop CS2 (Adobe Systems Inc., Mountain View, California). Specimens were deposited in the Herbarium of the University of Illinois at Urbana-Champaign (ILL) and the Herbarium of the University of Panama (PMA). Cultures were obtained and are maintained according to the procedures of Fallah and Shearer (2001) and are deposited in the University of Illinois Fungus Collection. Specimens collected and cultured in Thailand were deposited at BIOTEC Bangkok Herbarium (BBH) and BIOTEC Culture Collection (BCC), respectively.

	TAXONOMY

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Megalohypha A. Ferrer et Shearer, gen. nov.

Type species: Megalohypha aqua-dulces

Etymology: From the Greek "megalo" = big, large and "hypha" = hyphae

Ascomata superficialia, globosa vel obpyriformia, ostiolata, papillata, habentes vel sine stipite, ad substratum connexi per hyphas latas, brunneas, septatas, stoloniformes. Paries peridii cellularis magnis, hyalinis, tenuitunicatis. Hamathecium pseudoparaphysibus. Asci fissitunicati, clavati, brevipedicellati, octospori. Ascosporae brunneae vel fuscae, uniseptatae, symmetricae, tunicatae asperae, striis longitudinalis.

Ascomata superficial on wood, globose to obpyriform, ostiolate, papillate, stalked or sessile, connected to the substratum by broad, brown, septate, stoloniferous hyphae. Peridial wall of large, hyaline, thin-walled cells. Hamathecium pseudoparaphysate, pseudoparaphyses septate, branched, anastomosing above the asci. Asci fissitunicate, broadly clavate or fusiform, short pedicellate, 8-spored. Ascospores brown to dark brown, 1-septate, symmetrical, rough-walled, longitudinally striate.

Megalohypha aqua-dulces A. Ferrer et Shearer, sp. nov. FIGS. 1–14

View larger version (155K): [in this window] [in a new window]   FIGS. 1–6. Megalohypha aqua-dulces collected from wood (Holotype AF005-1). 1. Longitudinal section through ascoma. 2. Neck showing subglobose divergent cells. 3. Longitudinal section showing cells of peridium. 4. Hamathecium. 5–6. Asci. Bars: 1 =20 µm, 2–6 = 10 µm.

View larger version (58K): [in this window] [in a new window]   FIGS. 7–8. Megalohypha aqua-dulces collected from wood (Holotype AF005-1). 7. Ascospores. 8. Ascospore, arrow indicates sulcate striations. Bars: 7–8 = 10 µm.

View larger version (131K): [in this window] [in a new window]   FIGS. 9–14. Megalohypha aqua-dulces grown in culture (AF005-2). 9. Mycelium. 10. Sessile ascomata. 11. Stalked ascomata. 12. Asci. 13. Hamathecium. 14. Ascospores. Bars: 9, 12, 13 and 14 = 10 µm; 10 = 20 µm; 10 = 20 µm; 11 = 50 µm.

Ascomata on wood 240–300 x 200–250 µm, superficial, globose to obpyriform, ostiolate, papillate, hyaline, membranous, connected to substrate by a brown, septate stalk strongly constricted at the septa, 20–25 wide and up to 450 µm long; sessile ascomata connected to the substrate by superficial, wide, brown, septate, stoloniferous hyphae (FIG. 1). Papillae 55 x 45 µm, short, cylindrical, with inwardly growing, hyaline periphyses; wall of the papilla composed of outwardly diverging globose, thin walled cells (FIG. 2). Peridium about 15 µm thick, in longitudinal section composed of 1–2 layers of hyaline, thin-walled cells (FIG. 3). Pseudoparaphyses 3–4 µm wide, filamentous, septate, hyaline, branched and anastomosing above the asci (FIG. 4). Asci 110–160 x 35–60 µm, fissitunicate, clavate or ellipsoid, short pedicellate, with or without an apical chamber, 8-spored (FIGS. 5, 6). Ascospores 40–55 x 19–22 µm (mean = 48.3 x 18.8 µm, SD = 2.8 x 0.91 µm, n = 30), irregularly arranged, ellipsoidal, acutely tapered at apices, brown to dark brown, 1-septate, septum appearing as a dark band, both cells of equal shape and size, rough walled (FIG. 7) with longitudinal sulcate striations (FIG. 8) lacking appendages or a gelatinous sheath.

Colonies on potato-dextrose agar (PDA; Difco) effuse, with little aerial mycelium, slow growing, reaching 1.2 cm diam in 4 wk, dark brown and producing a pale yellow pigmentation of the surrounding agar. Hyphae brown, smooth, strongly constricted at the septa, 25–40 µm wide (FIG. 9). No anamorph was observed. Stalked and sessile ascomata formed on PDA slants after 1 mo incubation at 24 C. Ascomatal stalks of wide septate hyphae strongly constricted at the septa with a narrower hypha contained within (FIGS. 10, 11). Asci and ascospores were formed; asci were equipped with an apical chamber (FIG. 12) and ascospores were a lighter brown color (FIG. 14) than those formed on natural substrates; wider pseudoparaphyses (4–9 µm) were observed (FIG. 13) in ascomata formed in culture than in those formed on natural substrates.

Specimens examined. – PANAMA. COLON PROVINCE: Soberania National Park, Juan Grande River, 9°8'N, 79°43'W, 12 Jan 2003 on submerged decorticated wood, A. Ferrer, AF005-1. (ILL). HOLOTYPE.

Additional specimens examined. – PANAMA. COLON PROVINCE: Soberania National Park, Frijoles River, 9°8'N, 79°43'W, on submerged decorticated wood, 12 May 2003. A. Ferrer, AF005-2. THAILAND. KRABI PROVINCE: Than Bok Khorani National Park, Stream at Nature Trail, 8°23.6'N, 98°44.1'E, on submerged wood, 26 Jan 2006. S. Sivichai, SS3792.

Known distribution. – PANAMA (COLON), THAILAND (KRABI)

Etymology. – Aqua-dulces (aqua = water, dulces = sweet) in reference to its freshwater habitat.

	DISCUSSION

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Characteristics of this newly discovered fungus place it within the order Jahnulales. We have established a new genus for this fungus, Megalohypha, based on morphological differences with the existing genera in the Jahnulales, Aliquandostipite, Jahnula, and Patescospora. In addition molecular studies provide strong support for the placement of M. aqua-dulces on a single clade within the Jahnulales separate from the clades containing Aliquandostipite, Jahnula and Patescospora (Campbell J, Ferrer A, Raja HA, Sivichai S, Shearer CA unpublished data).

Megalohypha differs from all genera currently included in the Jahnulales in having vegetative hyphae and ascomatal stalks that are strongly constricted at the septa (FIGS. 9, 11). In addition the ascospores have bipolar symmetry, acute as opposed to rounded apices, a dark band at the midseptum (FIGS. 7, 8, 14) and sulcate striations on the ascospore wall (FIGS. 8, 14). In addition mature ascomata of Jahnula species are more strongly pigmented brown and have a thicker peridium than those of Megalohypha. Ascomata of Megalohypha however resemble those of Aliquandostipite in gross morphology, but ascospores of Aliquandostipite are more elongated in outline, lighter (hyaline to pale brown), the upper cell is slightly larger than the lower cell, are surrounded by a large gelatinous sheath (Inderbitzin et al 2001, Raja et al 2005) and do not have sulcate wall striations.

A unique characteristic among the Jahnulales is the presence of narrower hyphae enclosed within the hyphal stalk cells and vegetative hyphae that are the largest (10–40 µm wide) observed in the euascomycetes (Hyde and Wong 1999, Inderbitzin et al 2001, Pang et al 2002). Pang et al (2002) suggested that the wide vegetative hyphae might be an apomorphic character in the Jahnulales. The function of the wide vegetative hyphae is not yet understood, but because all species in the Jahnulales have been described from aquatic or wet habitats it might reflect an adaptation in this group to such habitats. Raja and Shearer (2006) and Vijaykrishna et al (2006) proposed that the broad, stoloniferous hyphae might play an important role in colonization and holding fungi onto softened wood in aquatic habitats.

Species in the order Jahnulales may play a role in decomposing organic matter in aquatic habitats; a recent study (Simonis J, Raja HA, Shearer CA unpublished data) shows that Megalohypha aquadulces can produce soft rot cavities in balsa wood.

	ACKNOWLEDGMENTS

 
We thank Huzefa Raja and Jim Dalling for reviewing the manuscript before submission. We appreciate the Smithsonian Tropical Research Institute (STRI) for its logistic support in Panamanian collection forays. Financial support by the National Science Foundation (NSF Grant No. DEB 0316496) is gratefully acknowledged. Biodiversity Research and Training Programme (BRT Thailand) with co-financing by the National Center for Genetic Engineering and Biotechnology (BIOTEC) and the Thailand Research Fund (TRF) grant No. BRT-145006 are thanked for supporting freshwater fungal research in Thailand.

	FOOTNOTES

 
Accepted for publication March 27, 2007.

¹ Corresponding author. E-mail: aferrer{at}life.uiuc.edu

	LITERATURE CITED

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS TAXONOMY DISCUSSION LITERATURE CITED

 
Fallah PM, Shearer CA. 2001. Freshwater ascomycetes: new or noteworthy species from north temperate lakes in Wisconsin. Mycologia 93:566–602.[CrossRef]

Huhndorf SM. 1991. A method of sectioning ascomycete herbarium specimens for light microscopy. Mycologia 83:520–524.[CrossRef]

Hyde KD, Wong SW. 1999. Tropical Australian freshwater fungi XV. The ascomycete genus Jahnula, with five new species and one new combination. Nov Hedwig 68:489–509.

Inderbitzin P, Landvik S, Abdel-Wahab A, Berbee ML. 2001. Aliquandostipitaceae, a new family for two new tropical ascomycetes with unusually wide hyphae and dimorphic ascomata. Am J Bot 88:52–61.[Abstract/Free Full Text]

Pang KL, Abdel-Wahab MA, Sivichai S, El-Sharouney HM, Jones EBG. 2002. Jahnulales (Dothideomycetes, Ascomycota): a new order of lignicolous freshwater ascomycetes. Mycol Res 106:1031–1042.[CrossRef]

Raja HA, Ferrer A, Shearer CA. 2005. Aliquandostipitate crystallinus, a new ascomycete species from wood submerged in freshwater habitats. Mycotaxon 91:207–215.

———, Shearer CA. 2006. Jahnula species from North and Central America, including three new species. Mycologia 98:319–332.[Abstract/Free Full Text]

Vijaykrishna D, Jeewon R, Hyde KD. 2006. Molecular taxonomy, origins and evolution of freshwater ascomycetes. Fungal Divers 23:367–406.

Volkmann-Kohlmeyer B, Kohlmeyer J. 1996. How to prepare truly permanent microscope slides. Mycologist 10: 107–108.

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