The genus Mortierella has been placed in a separate family, the Mortierellaceae, and is characterized by grey to yellowish grey, rapidly growing colonies that produce small delicate sporangia lacking a columella, on simple or branched sporangiophores. Sporangia may be one-spored or multi-spored and a collarette is typically left after the sporangial wall dissolves. Sporangiospores are one-celled, globose to ellipsoidal and chlamydoconidia may also be present. Mortierella species are common soil fungi and the genus contains over 70 recognized species, however, M. wolfii is probably the only pathogenic species to man and animals.
Cultures are fast growing, white to greyish white, downy, often with a broadly zonate or lobed (rosette-like) surface appearance and no reverse pigment. Sporangiophores are typically erect, delicate, 80-250 um in height, 6-20 um wide at the base, arising from rhizoids or bulbous swellings on the substrate hyphae and terminating with a compact cluster of short acrotonous (terminal) branches. Sporangia are usually 15-48 um in diameter, with transparent walls and a conspicuous collarette is usually present following dehiscence of the sporangiospores. Columella are generally lacking and sporangiospores are single-celled, short-cylindrical, 6-10 x 3-5 um, with a double membrane. Chlamydoconidia with or without blunt appendages (amoeba-like) may be present. Zygospores have not been observed. Temperature: grows well at 40-42C; maximum 48C. RG-2 organism.
Culture of Mortierella wolfii.
Sporangium with acrotonous (terminal) branches and rhizoids of M. wolfii.
Mortierella wolfii is an important casual agent of bovine mycotic abortion, pneumonia and systemic mycosis in New Zealand, Australia, Europe and USA. Confirmed human infections have not been documented. M. wolfii has also been isolated from soil, rotten silage, hay and coal spoil tips.
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.