Orbiliaceae

The Orbiliaceae are a family of saprobic sac fungi in the order Orbiliales. The family, first described by John Axel Nannfeldt in 1932, contains 288 species in 12 genera.[1] Members of this family have a widespread distribution, but are more prevalent in temperate regions.[2] Some species in the Orbiliaceae are carnivorous fungi, and have evolved a number of specialized mechanisms to trap nematodes.

Orbiliaceae
Orbilia xanthostigma
Scientific classification
Kingdom: Fungi
Division: Ascomycota
Class: Orbiliomycetes
Order: Orbiliales
Family: Orbiliaceae
Nannf. (1932)
Type genus
Orbilia
Fr. (1836)
Genera

Arthrobotrys
Brachyphoris
Dactylella
Dactylellina
Dicranidion
Duddingtonia
Dwayaangam
Gamsylella
Hyalorbilia
Monacrosporium
Orbilia
Pseudorbilia

A fungus of the genus Arthrobotrys, showing adhesive nets that it uses to trap nematodes.  Numbered ticks are 122 μm apart.

Description

Orbiliaceae do not have stromata, dense structural tissue that produces fruit bodies. They have small disc-shaped apothecia, that are typically convex, brightly colored or translucent.[2] Their ascospores are small (typically less than 10 x 1 μm), hyaline, and have an oval or ellipsoidal shape.[3] Species are usually found in wood on both wet and dry habitats.[2] Anamorph species are hyphomycetous.[4]

Nematophagy

This family is well known for its many nematophagous species.[5] Shortly after coming into contact with its prey, fungal mycelia penetrate the nematode and spontaneously differentiate into functional structures, known as traps, which will ultimately digest the nematode's internal contents.[6] There are 5 types of trap mechanisms recognized in this family:[6][7][8][9]

  • Adhesive network: the most common trap, formed by hyphal outgrowths that recurve into themselves to form nematode-trapping loops.
  • Adhesive knob: a roughly spherical cell, attached to the hyphae either directly or on an erect stalk. Adhesive knobs are typically closely spaced along a section of hyphae.
  • Nonconstricting rings: always found with the adhesive network traps, and formed from thickening hyphae that curve and fuse to the supporting stalk.
  • Adhesive column: a layer of cells on a hyphae with an adhesive surface.
  • Constricting rings: these are rings of hyphae that swell rapidly inwards upon contact with the nematode, quickly (in 1–2 seconds) "lassoing" the victim.

Genera

According to the most recent classification of Ascomycota,[10] the Orbiliaceae contain only two (teleomorph) genera, the Hyalorbilia and the Orbilia. Hyalorbilia is distinguished from Orbilia by having asci without a stalk that arise from croziers, a hemispherical to broadly conical, thin-walled apex, asci and paraphyses in a gelatinous matrix, and an ectal excipulum (the outer surface of a cup-like apothecium) of horizontal textura prismatica.[11][12]

Anamorph genera of the Orbiliaceae include Anguillospora,[13] Arthrobotrys,[14] Dactylella,[15] Dactylellina, Dicranidion,[16] Drechslerella, Helicoön,[17] Monacrosporium, and Trinacrium. It has been suggested that the anamorph specialization illustrates convergent evolution occurring among mycelial fungi in aquatic and low-nitrogen habitats.[18] This hypothesis has been borne out by recent phylogenetic and morphological studies.[19]

In 2007, a new species was described from southwestern China with morphological features intermediate between Orbilia and Hyalorbilia. This species, named Pseudorbilia bipolaris Y. Zhang, Z.F. Yu, H.O. Baral & K.Q. Zhang, was placed into its own genus in the Orbiliaceae to accommodate its distinctive features.[20]

References
  1. Kirk MP, Cannon PF, Minter DW, Stalpers JA (2008). Dictionary of the Fungi (10th ed.). Wallingford: CABI. p. 485. ISBN 978-0-85199-826-8.
  2. Cannon PF, Kirk PM (2007). Fungal Families of the World. Wallingford: CABI. p. 251. ISBN 978-0-85199-827-5.
  3. Blackwell M, Alexopoulos CJ, Mims CW (1996). Introductory Mycology. New York: Wiley. ISBN 0-471-52229-5.
  4. Bisby GR, Ainsworth GC, Kirk PM, Aptroot A (2001). Ainsworth & Bisby's Dictionary of the Fungi. Oxon: CAB International. p. 369. ISBN 0-85199-377-X.
  5. Pfister DH. (1997). Castor, pollux and life histories of fungi. Mycologia 89(1): 1-23.
  6. Barron, George L. (1977). The Nematode-destroying Fungi. Guelph: Canadian Biological Publications. ISBN 0-920370-00-4.
  7. Yang Y, Yang E, An Z, Liu X (2007). "Evolution of nematode-trapping cells of predatory fungi of the Orbiliaceae based on evidence from rRNA-encoding DNA and multiprotein sequences". Proc. Natl. Acad. Sci. U.S.A. 104 (20): 8379–84. doi:10.1073/pnas.0702770104. PMC 1895958. PMID 17494736."www.pnas.org" (PDF). Retrieved 2008-12-30.
  8. Drechsler C. (1937). Mycologia 29: 447–552.
  9. Stirling GR (1991). Biological control of plant parasitic nematodes. Wallingford, UK: C.A.B. International. ISBN 0-85198-703-6.
  10. "Outline of Ascomycota - 2007". Retrieved 2008-12-25.
  11. Baral HO. (1994). Comments on "Outline of the ascomycetes – 1993". Systema Ascomycetum 13: 113-128.
  12. Wu ML, Su YC, Baral HO, Liang SH. (2007). Two new species of Hyalorbilia from Taiwan. Fungal Diversity 25: 233–44.
  13. Webster J, Descals E. (1979). The teleomorphs of water-borne Hyphomycetes from fresh water. pp. 419–51. In: The Whole Fungus. Ed., Bryce Kendrick. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada.
  14. Pfister DH. (1994). Orbiliafimicola, a nematophagous discomycete and its Arthrobotrys anamorph. Mycologia 86: 451–53.
  15. Thakur S, Zachariah K. 1989. Response of the fungus Dactylella rhopalota to bacteria. Plants & Soil 120: 87–93.
  16. Korf RP. (1992). A preliminary discomycete flora of Macronesia: Part 8, Orbiliaceae. Mycotaxon 45: 503–10.
  17. Pfister DH. (1995). Helicoon sessile, the anamorph of Orbilia luteorubella. Inoculum 46: 34 (Newsletter of Mycological Society of America).
  18. Moore D, Rayner AD, Brasier CM (1987). Evolutionary Biology of the Fungi: symposium of the British Mycological Society held at the University of Bristol, April 1986. Cambridge, UK: Cambridge University Press. pp. 191–201. ISBN 0-521-33050-5.
  19. Li Y, Hyde KD, Jeewon R, Cai L, Vijaykrishna D, Zhang K (2005). "Phylogenetics and evolution of nematode-trapping fungi (Orbiliales) estimated from nuclear and protein coding genes" (PDF). Mycologia. 97 (5): 1034–46. doi:10.3852/mycologia.97.5.1034. hdl:10722/53351. PMID 16596955.
  20. Pseudorbilia gen. nov. (Orbiliaceae) from Yunnan, China. Fungal Diversity PDF
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