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Rhizomucor Mold Species

Rhizomucor species is a causative agent of Zygomycosis.

(Information from @ 2005)



Taxonomic Classifications


Kingdom: Fungi
Phylum: Zygomycota

Order: Mucorales

Family: Mucoraceae

Genus: Rhizomucor

Rhizomucor Mold Picture

Rhizomucor species with poorly developed rhizoid

Note the poorly developed rhizoid of Rhizomucor species as seen on the bottom left - side of the microscopic photograph above, viewed under 40X objective. 

The microscopic photograph of Rhizomucor species was taken by our Mold Microbiologist,

 Ma. Adee Light E. Hilado for mold microscopy documentation.




Rhizomucor is a cosmopolitan filamentous fungus that thrives in soil and decomposing fruit and vegetable matter.  Rhizomucor species are often isolated from composting or fermenting organic matter and they are also rare agents of serious to fatal infections in humans.  Except for Rhizomucor variabilis, Rhizomucor species are thermophilic in nature and can grow at temperatures as high as 54C. 



The genus Rhizomucor contains three species namely, Rhizomucor pusillus, Rhizomucor miehei, and Rhizomucor variabilis.  Rhizomucor variabilis is very close to Mucor hiemalis phylogenetically.  Maximum growth temperature, biochemical assimilation profile, thiamine dependency, and the diameter of the sporangia are the characteristics that aid in the differentiation of the three Rhizomucor species from each other.  Rhizomucor miehei is homothallic while Rhizomucor pusillus is either homo - or heterothallic.


Pathogenicity and Health Effects

Rhizomucor species are occasional agents of angio invasive disease referred to as zygomycosis, which is often considered as fatal.  The most frustrating features of this disease are vascular invasion that causes necrosis of the infected tissue, and perineural invasion.  Rhizomucor pusillus is seldom an agent of cutaneous, pulmonary, rhinofacial, and disseminated zygomycosis especially infecting neutropenic patients with hematological malignancies and diabetes mellitus.  Otherwise healthy individuals have been reported with cutaneous infections caused by Rhizomucor variabilis.  Aside from human infections, animal infections are common as well such as bovine mycotic abortion due to Rhizomucor species. 


Macroscopic Appearance

     Growth rate is very rapid and colonies are typically cotton candy like in texture;

     The surface colony color is initially white becoming gray to yellowish brown in time while reverse is white to pale; and

     Rhizomucor species other than Rhizomucor variabilis are thermophilic and yield optimum growth at temperatures as high as 54C.


Microscopic Appearance

      Non septate or scarcely septate broad hyphae, rudimentary rhizoids, sporangiophores, sporangia, and sporangiospores are present;

      Rudimentary rhizoids are located on stolons between the sporangiophores but are often rare or difficult to recognize;

      Sporangiophores are irregularly branched, with branches sometimes arranged in an umbel at the apex;

      Sporangia are brown in color, round - shaped, with well developed columella, and with diameter ranging from 40 80 m;

      Sporangiospores are small, round or oval in shape, unicellular, and with diameter ranging from 3 4 m;

      Apophysis is absent;

      If present, zygospores are formed in the aerial hyphae, round to slightly compressed, and dark brown to blackish in color;

      The microscopic morphology of Rhizomucor appears to be intermediate between that of Rhizopus and Mucor;

      Rhizomucor species differ from Mucor by having the ability to grow at 50 - 55C and by having rhizoids and stolons;

      Rhizomucor species differ from Rhizopus by having branched sporangiophores and rhizoids not arising opposite the sporangiophores; and

      Rhizomucor species differ from Absidia by having globose sporangia and sporangiophores that are not swollen where they join together with the columellae.


Laboratory Precautions

General laboratory precautions are required, no special safety measures needed.



In vitro susceptibility data are not available for Rhizomucor species.


Treatment of Rhizomucor infections includes antifungal and surgical therapy, which is also similar to the treatment of zygomycosis caused by fungi belonging to class Zygomycetes.  For antifungal treatment, amphotericin B is most commonly used such as liposomal amphotericin B.  Early diagnosis and treatment are vital and mortality rate is high. 

The mycological information gathered and
organized in this extensive research on different
Pathogenic Molds was sourced out from the list of
informative websites and reference below:

A Clinical Laboratory Handbook: Identifying Filamentous Fungi by St. Germain, Guy and R. Summerbell.


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