''Mucor circinelloides'' is a dimorphic fungus belonging to the Order Mucorales (Phylum Mucoromycota). It has a worldwide distribution, found mostly in soil, dung and root vegetables. This species is described as not known to be able to produce mycotoxins, however it has been frequently reported to infect animals such as cattle and swine, as well as fowl, platypus and occasionally humans. Ketoacidotic patients are particularly at risk for infection by ''M. circinelloides''.

History and taxonomy

''Mucor circinelloides'' is one of the common species in the genus ''Mucor''. ''Mucor circinelloides'' is a variable species that include several variants such as; ''M. circinelloides'' f. ''circinelloides''; ''M. circinelloides'' f. ''lusitanicus''; ''M. circinelloides'' f. ''griseocyanus'' and ''M. circinelloides'' f. ''janssenii''.

Growth and morphology

''Mucor circinelloides'' reproduce asexually. The sporangiophores are found as two types: elongate and

sympodial Sympodial growth is a bifurcating branching pattern where one branch develops more strongly than the other, resulting in the stronger branches forming the primary shoot and the weaker branches appearing laterally. A sympodium, also referred to a ...

ly branched. The elongate sporangiophores have larger

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...

, which are white at first and progressively turn greenish brown in colour. They assume a

globose A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ...

shape and are 40-80 μm in size; characterized as "bobbing heads". Sporangiophores are mostly sympodially branched with small sporangia (25 μm); branches are and sometimes circinate. The diameter of the sporangia range from 20 to 80 μm. Sporangia have slightly encrusted walls. In larger sporangia, the membranes are

deliquescent Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...

, whereas they are persistent in the smaller ones and rupture at maturity. Smaller sporangia also have smooth persistent walls. Sporangiophores are

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ...

(6-7 μm in diameter) or subglobose (4-6 μm in diameter). Numerous

chlamydospores A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as ''Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable c ...

are also produced. Colonies are fast growing and go up to 2 cm in height. On

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Yeast Autolysate (CYA) plates, the colony growth is low and sparse, most often spreading across the entire Petri dish. These colonies of 60 mm diameter or more appear to be pale grey or yellow in colour, with the reverse being uncoloured. Colonies also fill up the entire Petri dish of malt extract agar, producing colony colours similar to those observed on CYA. ''Mucor circinelloides'' can assume a yeast-like growth form. It has been isolated in this yeast form from human urine and normal stool specimen. It has also been recovered as a yeast from frogs.

Physiology

''Mucor circinelloides'' has good growth and

sporulation In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae ...

between 5-10 ℃ and very poor growth at 37 ℃ which is also the maximum growth temperature. The minimal water activity(a_w) for growth is 0.9. ''M. circinelloides'' assimilates ethanol and nitrate. The length and number of tall sporangiophores decrease with lower temperatures. Spores are broadly

(4.4-6.8 x 3.7-4.7 µm Growth, sporulation, and presence of tall and short sporangiophores can be influenced by temperature; however sporangiophore shape, size and uniformity are not influenced by temperatures.

Habitat and ecology

At least 20 species belonging to the genus ''Mucor'' are found to be extracted from food. ''M. circinelloides'' is one of the five most significant fungus out of these 20 along with ''M. hiemalis'', ''M. piriformis'', ''M. plumbeus'' and ''M. racemosus''. It has been reported to spoil cheese and yams as well as diseases of mango. This fungus has also been isolated from various foods such as meat, hazelnuts, walnuts, maize, mung beans, soybeans and barley. Fungi in the order Mucorales class have not been investigated in detail for their ability to produce mycotoxins; Cytotoxicity and mycotoxin-production was analysed and tested for using the cytotoxicity test ( MTT assay) and LC/MS/MS-based multimycotoxin method respectively for three fungal species, including ''M. circinelloides''. ''Mucor circinelloides'' was found to be able to produce 3-nitropropionic acid as well as have low cytotoxicity. Conventionally, ''M. circinelloides'' is considered not to produce mycotoxins.

Pathogenicity

''Mucor circinelloides'' is considered an emerging pathogen, although it has only been associated rarely with very human disease and have been limited to

cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

infection. This species is occasionally isolated from humans, birds, cattle, and swine.

Antioxidant potential

''Mucor circinelloides'' is potentially a rich source of antioxidants and other secondary metabolites which could be used in the development of

nutraceutical A nutraceutical or bioceutical is a pharmaceutical alternative which claims physiological benefits. In the US, "nutraceuticals" are largely unregulated, as they exist in the same category as dietary supplements and food additives by the FDA, unde ...

s and natural antioxidants.

References

{{Taxonbar , from = Q6931245 Mucoraceae Fungal plant pathogens and diseases Fungi described in 1875