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School of Molecular & Biomedical Science
The University of Adelaide

Dr David Ellis

Basidiobolus ranarum

Synonyms: Basidiobolus meristosporus; Basidiobolus haptosporus; Basidiobolus heterosporus.

Colonies are moderately fast growing at 30C, flat, yellowish-grey to creamy-grey, glabrous, becoming radially folded and covered by a fine, powdery, white surface mycelium. Note, satellite colonies are often formed by germinating conidia ejected from the primary colony.  Microscopic examination usually shows the presence of large vegetative hyphae (8-20 um in diameter) forming numerous round (20-50 um in diameter), smooth, thick-walled zygospores that have two closely appressed beak-like appendages. Two types of asexual spores are formed: primary and secondary. Primary spores are globose, one-celled, solitary and are forcibly discharged from a sporophore. The sporophore has a distinct swollen area just below the spore that actively participates in the discharge of the spore. Secondary spores are clavate, one-celled and are passively released from a sporophore. These sporophores are not swollen at their bases. The apex of the passively released spore has a knob-like adhesive tip. These spores may function as sporangia, producing several sporangiospores. Note, isolates often lose their sporulating ability with subculture and special media incorporating glucosamine hydrochloride and casein hydrolsate may need to be used to stimulate sporulation.  RG-2 organism.

Culture of Basidiololus ranarum
Culture of Basidiololus ranarum.

Zygospores of Basidiobolus ranarum
Zygospores of Basidiobolus ranarum.

Asexual spores of B. ranarum
Asexual spores of B. ranarum.
Note typical swollen sporophore in lower right corner

Clinical significance:

Basidiobolus ranarum is commonly present in decaying fruit and vegetable matter, and as a commensal in the intestinal tract of frogs, toads and lizards. It has been reported from tropical Africa, India, Indonesia and South East Asia including the Northern Territory of Australia.

Mycosis: Subcutaneous Zygomycosis

Further reading:

Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA