KINGDOM EUMYCOTA - The
True Fungi
PHYLUM ZYGOMYCOTA
Characteristics of Zygomycetes
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Hyphae are non septate and coenocytic (i.e., non-septate - no cross-walls).
Cell walls contain chitin.
Flagellated spores are absent.
Reproduce asexually by producing sporangiospores within a special sac called the sporangium.
Sporangium types (4 types)
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Sexual spores are called zygospore(s) contained within a zygosporangium (Refer to Figures 4-2 and 4-3 on
pages 85 and 86 in the textbook).
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True sporangium - refer to Figure 4-1 on page 83 in the textbook
Sporangioles - much smaller than true sporangia. No columella produced and few spores - refer to Figure 4-6 on page 89 in the
textbook.
Monosporous sporangium (one-spored sporangium) - refer to Figure 4-7b on page 90 in the textbook.
Merosporangium - sac containing 10-15 sporangiospores that occur in a linear sequence - superficially it looks a lot like an ascus,
but it is not.
A. F. Blakeslee in 1904 discovered that many of these fungi are heterothallic, that is, they require two compatible partners to
produce sexual spores.
Sex hormones are known to facilitate sexual reproduction among some zygomycetes. For example, hyphae of Mucor species for
the + and - mating strains are known to produce trisporic acids which are volatile (+ strain yields 4-hydroxymethyltrisporates; strain yields trisporins) and diffuse through the air. Volatiles stimulate progametagia production and the synthesis of carotene (a
precursor for trisporic acids) and trisporic acids. A positive feedback mechanism is formed between the two compatible strains
leading to physical contact of progametagia and sexual reproduction - refer to the pages 314-315 in the textbook.
Heterothallism (Gr. heteros = different from, thallos = shoot; the condition of being self-sterile, requiring a partner for sexual
reproduction) and homothallism (Gr. homos = alike, thallos = shoot; the condition of being self fertile; able to reproduce sexually
without a partner) exhibited among species in this phylum.
Two major classes
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Zygomycetes
Trichomycetes
Cell Walls
• Cell walls
contain chitin.
Asexual Reproduction
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Reproduce asexually by producing
sporangiospores within a special
sac called the sporangium.
Sporangium types (4 types)
– True sporangium - refer to Figure
4-1 on page 83 in the textbook
– Sporangioles - much smaller than
true sporangia. No columella
produced and few spores - refer
to Figure 4-6 on page 89 in the
textbook.
– Monosporous sporangium (onespored sporangium) - refer to
Figure 4-7b on page 90 in the
textbook.
– Merosporangium - sac containing
10-15 sporangiospores that occur
in a linear sequence - superficially
it looks a lot like an ascus, but it is
not.
Sexual Reproduction
• Sexual spores are called zygospore(s) contained within a
zygosporangium (Refer to Figures 4-2 and 4-3 on pages 85 and
86 in the textbook).
– A. F. Blakeslee in 1904 discovered that many of these fungi are
heterothallic, that is, they require two compatible partners to produce
sexual spores.
– Sex hormones are known to facilitate sexual reproduction among some
zygomycetes. For example, hyphae of Mucor species for the + and mating strains are known to produce trisporic acids which are volatile (+
strain yields 4-hydroxymethyltrisporates; - strain yields trisporins) and
diffuse through the air. Volatiles stimulate progametagia production and
the synthesis of carotene (a precursor for trisporic acids) and trisporic
acids. A positive feedback mechanism is formed between the two
compatible strains leading to physical contact of progametagia and
sexual reproduction - refer to the pages 314-315 in the textbook.
– Heterothallism (Gr. heteros = different from, thallos = shoot; the
condition of being self-sterile, requiring a partner for sexual
reproduction) and homothallism (Gr. homos = alike, thallos = shoot;
the condition of being self fertile; able to reproduce sexually without a
partner) exhibited among species in this phylum.
Phylum Zygomycota: Classes
• Two major classes
– Zygomycetes
– Trichomycetes
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http://www.tolweb.org/Zygomycota
Zygomycetes (Order Mucorales)
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Members of this group are the "weeds" of the fungal world
Common genera include Mucor, Absidia, Rhizopus, and Pilobolus.
Grow and invade quickly on easily digestible substrates, such as those
containing starches, sugars, and hemicelluloses
Group lacks ability to degrade complex carbohydrates like cellulose
Some are mycorrhizal, especially on monocots
Can act as parasites and/or cause diseases in plants (soft rot of fruits and
vegetables), animals (predatory on nematodes and some insects and
humans (zygomycosis - sometimes referred to as mucormycosis or
phycomycosis)
– In humans, such diseases are opportunistic and occur in an
immunocompromised person (e.g., uncontrolled diabetes, AIDS)
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Industrial uses of these fungi include production of metabolites (e.g.,
amylases, rennins, alcohol, and various organic acids - lactic acid, citric
acid, succinic acid, oxalic acid)
Growth of fungi used to modify foods, in production of tempeh or tempe and
Chinese cheese (sufu) - refer to pages 538-539 in the textbook.
Tempeh
Rhizopus oligosporus is used to partially
digest the proteins of soybeans. The
result is a food product called tempeh
(produced in Indonesia, New Guinea and
other parts of SE Asia), which is
nutritionally enriched (increased
digestibility of proteins, higher levels of
riboflavin, niacin, and B12)
• How to make Tempeh:
– Soybeans are soaked overnight and
dehulled.
– Soybeans are cooked by boiling for
1/2 hour.
– After cooling, beans are inoculated
with Rhizopus oligosporus by adding
pieces of tempeh from a previous
batch, using a wrapper from former
batch, or by adding a spore
suspension in water from a culture
– The beans are wrapped (e.g.,
leaves, plastic) and then incubated
at room temperature for about 24
hours
– Tempeh is sliced, dipped in salt
water and cooked.
Pilobolus
Zygomycosis
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in humans, disease is manifested in highly stressed or debilitated individuals
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metabolic acidosis
immunosuppression
trauma
in animals and some cases in humans, disease is manifested after exposure to large
quantities of a particular fungi or spores (e.g., contaminated feed, aerosols of fungal
spores).
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Phycomycosis and mucormycosis are older names that refer to diseases caused by
phycomycetes (obsolete taxonomic designation which included the zygomycetes,
oomycetes, and chytrids). Mucormycosis referred to diseases caused by members of the
Order Mucorales in the Zygomycetes.
Entomophthoromycosis Conidiobolae is synonymous with rhinofacial zygomycosis
caused by Conidiobolus coronatus which is also a parasite of insects and associated with
decaying plant debris.
Entomophthoromycosis Basidiobolae is a chronic subcutaneous form of zygomycosis
caused by Basidiobolus ranarum or B. haptosporus. Fungus is common on decaying
vegetation, soil and in the excrement of frogs.
General forms of Zygomycosis
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most acute and rapidly fatal fungal disease
some patients die within one week after the onset of symptoms
death rate was about 90%, but now it is about 50 %
uncontrolled diabetes with acidosis, acidosis caused by excessive aspirin intake, diarrhea, uremia, or
leukemia, lymphoma, severe burns, and other diseases
incidence of zygomycosis is on the increase due to immunosuppressant drugs, cortisone (steroids),
and other drugs
Etiologic agents include: Rhizopus arrhizus and other species; Absidia corymbifera, Mucor spp., and
Mortierella spp.
Rhinocerebral Zygomycosis
• nasal and orbital infection
• encephalitis
• invasion of larger blood
vessels and arteries
• patient may go into coma and
die
– Mark Tatum of Kentucky
(seen below; after surgery,
with and without facial
prosthetic) survived from
rhinocerebral zygomycosis
in 2000. Surgery was
required to remove infected
tissue. He died five years
later on February 26, 2005.
Zygomycetes - Order
Entomophthorales
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Zygomycetes (Order Entomophthorales)
Members of this order are predominately parasites of
insects and other arthropods
Entomophthora (more than 40 species recognized) and
Massospora are insect parasites
Entomophthora muscae kills house flies.
– Flies are sometimes found attached to window
panes, surrounded by a halo of sporangia
(sometimes referred to as conidia) that are
forcibly discharged from sporangiophores which
emerge between the abdominal segments.
– Fungus invades insect after contact with
sporangium. A germ tube forms and penetrates
the host. Insect becomes restless and exhibits
behavioral changes.
– After 5 to 8 days, host crawls to elevated position
(e.g., blade of grass, twigs, window panes,
etc.) Death often occurs between 3:00 to 7:00
pm.
– Host is attached to surface by rhizoids,
sporangiophores form and push out between the
abdominal segments sporangia are forcibly
discharged as turgor pressure builds up in the
sporangiophore. The sporangium may be shot
as far as 1.0 to 1.5 cm away from host.
– Entomophthora muscae: Dispersal of the
explosive dispersal of the sporangium - refer to
Figure 12-5b page 342 in the textbook.
– Zygospores may form within the body cavity of
the housefly.
Zygomycetes - Order Entomophthorales
• Massopspora cicadina is a parasite on the 17 year locust.
– Sporangia are produced in clusters with the body
cavity in the abdomen that are not forcibly discharged.
– Later infections, posterior portions of the abdomen
drop away successively, exposing sporangia.
– Insect will continue to fly around with only a head and
thorax.
– Zygospores my form with the abdomen with time.
– Entomophthora coronata (AKA Conidiobolus
coronatus) - parasitic on humans, horses and
insects. In humans, subcutaneous infection is called
Entomophthoromycosis Conidiobolae.
Zygomycetes - Order Entomophthorales
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Basidiobolus ranarum is associated with the dung of frogs and represents a
saprophyte.
– Sporangia (AKA conidia) are forcibly discharge. Turgor pressure created by
contraction of the elastic sporangiophore wall causes a tear in the sporangial wall
lifting the sporangium away from the dung. The sporangium and "skirt" travel
about 0.5 cm. The skirt detaches from the sporangium and the sporangium
continues to travel an additional distance of 1-2 cm. This form of explosive "spore"
dispersal has been referred to as a "two stage rocket" form of propulsion created
by the rushing of fluid out of the expelled skirt. Momentum carries the sporangium
the remaining distance.
– This fungus also produces sporangioles (also called capilliconidia with haptor)
which are sticky and catch onto passing insects, like beetles. The fungus is
thought to re-enter the amphibian or reptiles digestive track when the animal eats
a tainted beetle. In the stomach the capilliconidia cleaves into a number of
spores. Upon voiding their excrement, the fungus mycelium grows and produces
more sporangia (AKA conidia) and sporangioles (AKA capilliconidia).
– Disease is called Entomophthoromycosis Basidiobolae (a form of zygomycosis in
humans in which tumor like enlargements develop in the subcutaneous tissue) was
once thought to be caused by a species other than Basidiobolus ranarum (called
Basidiobolus haptosporus). However isolates obtained from infected tissues in
humans appears to be B. ranarum and not a distinct separate species.
– Basidiobolus: Dispersal of the explosive dispersal of the sporangium; the two
stage rocket - refer to Figure 12-5a on page 342 in the textbook.
Rhinofacial and Chronic
Subcutaneous Zygomycosis
• Entomophthoromycos
is Conidiobolae and
Entomophthoromycos
is Basidiobolae
represent forms of
zygomycosis (fungal
diseases caused by
zygomycetes).
Phylum Zygomycota Class Trichomycetes
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Trichomycetes are obligately ssociated with an arthropod host; these fungi do not grow independently of their
hosts in nature.
Arthropod hosts include, insect larvae, crayfish, millipedes, beetles and isopods; not found in predacious
arthropods, only detritivores.
Hosts may live on land or in fresh or marine waters.
These fungi are usually found in the gut but one genus Amoebidium (probably not really a trichomycete) is found
on the outer surace of the host.
Thalli are attached to host by a holdfast that penetrates the lining of the gut or exoskeleton only and does not
penetrate living tissue.
Trichomycetes are generally considered to be commensals (trichomycete benefits from interaction but neither
benefits nor harms the host), although exceptions may exist.
– One study suggest that under sub optimal nutritional conditions the fungus (Smittium culisetae) may aide in
survival and development of the host. Mosquito larvae, Aedes aegypti, raised axenically on semidefiied
media not give adequate amounts of riboflavin do not survive well and none pupate, however with fungus
were present about 50% of infested larvae were still alive at the 4th instar and about half pupated.
– One species, Smittium morbosum, kills mosquito larvae (midgut epithelium is penetrated and larvae die due
to an inability to shed their molts).
Four Orders are found in this group; only members from one order (Harpellales) has been cultured.
The asexual propagative structure is the "trichospore" - consists of an elongated sporangium that contains a single
sporangiospore. Trichospores have a collar and an appendage that serves to entangle it in debris.
"Trichospores" explosively extrude their spore as it passes through the gut of a suitable host. This is followed by
holdfast formation. Spores are released form gut when host defecates, molts, or dies. For example, in species of
Smittium, germination and attachment occur within a half hour of ingestion of the spores.
In Smittium species extrusion of the sporangiospore and holdfast formation occur in two stages.
Trichospores are initially preconditioned in the midgut by exposure to potassium largely supplied by the insect's
excretory organs and high pH (pH 10)
The pH drops to 7 as spores pass through the hindgut and the "spores" extrude and become attached to the
cuticle of the gut. This process was discovered and studied in vitro and in vivo by Dr. Bruce Horn in the laboratory
of Dr. Robert Lichtwardt (University of Kansas).
Zygospores may be produced, but are seen only in dissected gut material, and only once in culture.
Trichomycetes: Smittium
• Figure A: "Trichospores" one-spored sporangia.
• Figure B: "Zygospores" one-spored zygosporangia
• Figure C: A zygospore - a
one-spored
zygosporangium