Mucor mucedo, commonly known as the common pinmould,
Growth and morphology
Mucor mucedo has fast growing colonies and are characterized by tall, simple, unbranched
lacking basal rhizoids, non-apophysate
sporangia, and pigmented
Zygosporangium walls.
The walls are covered with granules and the swollen apex contains
spores that are white or yellow in when immature, and upon maturation appear brownish grey or dark grey.
Colonies commonly have a fluffy appearance with heights of up to several centimeters, resembling cotton candy, and the hyphae are non-septate or sparsely septate.
is
heterothallic, and both (+) and (-) mating strains are morphologically indistinguishable although isolates of the (-) strain may exhibit less vigorous mycelial growth in cultivation.
The zygophores are highly differentiated from sporangiophores and are known to rarely bare sporangia.
morphology and growth is influenced by temperature:
-
30 °C - No growth
-
5-25 °C - Growth and sporulation
-
15 °C and below - Recurved short sporangiophores, columellae more narrow and cylindrical-ellipsoidal, larger
Mucor mucedo reproduction occurs in asexual and sexual methods.
Mucor mucedo is also influenced by light, as cultures grown during the day at 20 °C mainly produced tall sporangiophores, rarely producing short sporangiophores or none at all.
Reproduction
Asexual reproduction occurs by the formation of uninucleate,
haploid sporangiospores in the sporangia, on the terminal ends of the aerial sporangiophores. In the sporangia, there is an accumulation of nutrients, cytoplasm, and nuclei. An extension of the sporangiophore called the
columella protrudes into the sporangium, and upon the maturation of the sporangiospores, burst of the sporangium allows for the dispersion of the spores, where wind is the primary dissemination method.
Asexual reproduction may be favoured in unfavourable environmental conditions, as this inhibits the conjugation between the two sexual strains.
The (-) strain loses sexual capacity faster than the (+) strain.
As Mucor mucedo are heterothallic, the hyphae taking part in the sexual reproduction have to be of two different strains, either (+) or (-). When these make contact an extension of the hyphae called progametangia are formed and most of the nuclei and cytoplasm accumulate at the ends.
Physiology
Mucor mucedo is sensitive to the
fungicide captafol (terrazol) which inhibits the apical growth of hyphae and, at lower concentrations, promotes thickening of the fungal cell wall.
Terrazol, with its
fungistatic effect, induces liberation in
phospholipases within the
mitochondria and other membranes, leading to a complete lysis of the mitochondria.
The only known
antidote for the effect of terrazol is impure
saccharose, which contains phospholipase inhibitors. The cell wall thickening appears to be a side effect of the lowered phosphorylating capability of the mitochondria.
Pentachloronitrobenzene (PCNB) causes lysis of the internal structure of the mitochondria in
M. mucedo, and the observed effect differs from that of terrazol. PCNB increases the perinuclear space and the number of
vacuoles in the cell, and a pathological thickening of the cell wall is also observed.
The cell wall thickening occurring in
M. mucedo is induced by some fungicides, N2 atmosphere, and high concentrations of
glucose in growth media. The appears to be similar to the changes observed when transforming from mycelial to yeast form in
dimorphic fungi.
Habitat and ecology
Mucor mucedo has world-wide distribution, and are commonly discovered in
Canary Islands,
Egypt,
Great Britain,
Ireland,
Kenya,
Netherlands,
Australia,
Sri Lanka,
Ukraine,
China, and
Canada.
is easily found in dry horse dung around March and April and have the common habitat of soil, dung, water, nose effluent of cow, composted
leaf litter, stored grains, and many plants and fruits, such as grapes and tomatoes.
It interacts with some animals but are not frequent causative agents of disease, including
horse,
rabbits,
mice, and
rats.
grows well on cheese and produces the 'cat hair' defect, which is white mould forming on cheese with long, grey, hyphae, giving it the appearance of cat hair.
Mucor mucedo has been found to degrade polycyclic aromatic hydrocarbons (PAHs), a common soil pollutant and contaminant causing high concern, as contamination continues to increase. The species are highly efficient in biodegrading residual PAH in the soil, significantly decreasing it in within 12 days of introduction.
Mycotoxins
Mucor mucedo produces
oxalate, or oxalic acid, a simple dicarboxylic acid that is one of the terminal metabolic products of many fungi and plants. It is well known to be toxic to higher animals, including humans, due to its local corrosive effect and affinity for calcium ions, which oxalate reacts with to form water-insoluble calcium crystals.
also produces
aflatoxins, which are known to cause
liver cancer and other digestive, urinary, endocrine, haematopoetic, reproductive, and circulatory complications, although this requires further confirmatory studies as aflatoxins are mainly characteristic of
Aspergillus species.
The ability for
mycotoxins to diffuse from the mycelium into the environment depends on its
water solubility. Products with high water content, notably cheese and dough, allow significant diffusion of mycotoxins. Aflatoxins have been observed to diffuse into food products without extensive mycelial growth into the food.
Human disease
Mucor mucedo sometimes cause opportunistic and rapidly spreading infections called
mucormycosis. Also referred to as
zygomycosis, this necrotizing infection can be life-threatening in
diabetic or immuno-suppressed/compromised patients.
can cause minor infections as well, as there have been reported cases of frequent vomiting and severe purging along with
prostration following the consumption of cheese contaminated with
M. mucedo mould growth.
Amphotericin B
Amphotericin B, a drug primarily used for treatment of patients with progressive and potentially life-threatening fungal infections, has been found to be a potent inhibitor of
M. mucedo at concentrations of the drug ranging from 0.03 to 1.0 mcg/mL
in vitro.
Amphotericin B functions by binding to
sterols in the cell membrane of fungi leading to change in membrane permeability allowing leakage of intracellular components.
