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Laboratory Methods

School of Molecular & Biomedical Science
THE UNIVERSITY OF ADELAIDE
AUSTRALIA 5005

Contact:
Dr David Ellis

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Apophysomyces elegans

Colonies are fast growing, white becoming creamy white to buff with age, downy with no reverse pigment, and are composed of broad, sparsely septate (coenocytic) hyphae typical of a zygomycetous fungus.  Sporangiophores are unbranched, straight or curved, slightly tapering towards the apex, up to 200 um long, 3-5 um in width near the apophysis, and hyaline when young but developing as the culture ages, a sepia to brown pigmentation and a conspicuous sub-apical thickening 10-16 um below the apophysis with age.  Sporangiophores arise at right angles from the aerial hyphae and often have a septate basal segment resembling the "foot cell" commonly seen in Aspergillus.  Rhizoids are thin-walled, sub-hyaline and predominantly unbranched.   Sporangia are multispored, small (20-50 in diameter), typically pyriform in shape, hyaline at first, sepia colored when mature, columellate and strongly apophysate.  Columellae are hemispherical in shape and the apophyses are distinctively funnel- or bell-shaped.   Sporangiospores are smooth-walled, mostly oblong, occasionally subglobose, (3-4 x 5-6 um) and sub-hyaline to sepia in mass.   Good growth at 26, 37 and 42C.  RG-2 organism.

Culture of Apophysomyces elegans

Young sporangium (left) and mature sporangium (right) of
Apophysomyces elegans showing distinctive funnel-shaped apophyses and
a conspicuous pigmented sub-apical thickening below the apophysis.

Apophysomyces elegans is readily distinguishable from other zygomycetes of medical importance, especially the morphologically similar, strongly apophysate pathogen Absidia corymbifera. A. elegans has sporangiophores with distinctive funnel- or bell-shaped apophyses and hemispherical-shaped columellae, a conspicuous pigmented sub-apical thickening which constricts the lumen of the sporangiophore below the apophysis, and distinctive foot cells.

MIC data is limited.  Antifungal susceptibility testing of individual strains is recommended.

Agar block method to induce sporulation
of Apophysomyces elegans.

Laboratory identification of some zygomycetous fungi, especially Apophysomyces elegans and Saksenaea vasiformis may be difficult or delayed because of the mould's failure to sporulate on the primary isolation media or on subsequent subculture onto potato dextrose agar. Sporulation may be stimulated by the use of nutrient deficient media, like Czapek Dox agar, cornmeal-glucose-sucrose-yeast extract agar, or by using the agar block method described by Ellis and Ajello (1982).  Briefly, a small block of agar is cut from a well established culture grown on PDA and is placed in the centre of petri dish containing 1% agar in distilled water. After 21 days at 26C look for sporangium formation at the periphery of the petri dish.

Clinical significance:

Apophysomyces elegans is a rare human pathogen usually associated with invasive lesions following traumatic implantation of the fungus through the skin. It is a soil fungus with a tropical to sub-tropical distribution.

Mycosis: Zygomycosis

Further reading:

Ellis, D.H. 1997. Zygomycetes. Chapter 16 In Topley and Wilson's Microbiology and Microbial Infections. 9th edition Edward Arnold London pp247-277.

Ellis, J.J., and L. Ajello. 1982. An unusual source of Apophysomyces elegans and a method of stimulating sporulation of Saksenea vasiformis. Mycologia 74:144-145.