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School of Molecular & Biomedical Science
The University of Adelaide

Dr David Ellis

Rhizopus oryzae

Synonym: Rhizopus arrhizus

Culture of Rhizopus oryzae
Culture of Rhizopus oryzae.

On Sabouraud's dextrose agar, colonies are very fast growing at 25C, reaching 5-8 mm in height, with some tendency to collapse, white cottony at first, becoming brownish grey to blackish-grey depending on the amount of sporulation. Sporangiophores up to 1500 um in length and 18 um in width, smooth walled, non-septate, simple or branched, arising from stolons opposite rhizoids usually in groups of 3 or more. Sporangia are globose, often with a flattened base, greyish black, powdery in appearance, up to 175 um in diameter and many spored. Columella and apophysis together are globose, subglobose or oval, up to 130 um in height and soon collapse to an umbrella-like form after spore release. Sporangiospores are angular, subglobose to ellipsoidal, with ridges on the surface, and up to 8 um in length. No growth at 45C; good growth at 40C.

R. oryzae
Sporangiophores, rhizoids and sporangia of R. oryzae.

Sporangium with collapsed columella
Sporangium with collapsed columella and sporangiospores of R. oryzae.

Clinical significance:

Rhizopus oryzae (=R. arrhizus) is the most common causative agent of zygomycosis, accounting for some 60% of the reported culture positive cases, and nearly 90% of the rhinocerebral forms of infection. R. oryzae has a world-wide distribution with a high prevalence in tropical and subtropical regions. It has been isolated from many substrates, including a wide variety of soils, decaying vegetation, foodstuffs, and animal and bird dung. R. oryzae is often used in the production of fermented foods and alcoholic beverages in Indonesia, China and Japan. However, it also produces the ergot alkaloid agroclavine which is toxic to humans and animals.

Mycosis: Zygomycosis

Further reading:

Domsch, K.H., W. Gams, and T.H. Anderson. 1980. Compendium of soil fungi. Volume 1. Academic Press, London, UK.

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