PHYLUM ZYGOMYCOTA
- Hyphae are non septate and coenocytic (i.e., non-septate - no cross-walls).
- Cell walls contain chitin, chitosan, and polyglucuronic acid.
- Flagellated spores are absent.
- 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 (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.
- 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.
- Two major classes
- Zygomycetes
- Trichomycetes
- 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)
- 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.
- 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 Surinam), 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.
- How to make 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 Surinam), which is nutritionally enriched
(increased digestibility of proteins, higher levels of riboflavin,
niacin, and B12)
- Mucorales Lab Exercise: MS Word Document File
- Pilobolus:
Phototropism of the sporangiophore and dispersal of the explosive dispersal
of the sporangium - - refer to pages 338-342
in the textbook.
- The fungus shotgun: go to http://herbarium.usu.edu/fungi/FunFacts/pilobfct.htm. The following two Figures were downloaded from http://herbarium.usu.edu/fungi/FunFacts/pilobfct.htm on 11-10-2005.
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.
- Links to photographs and other information on Entomophthora muscae.
- 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.
- 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.
- Entomophthoromycosis Conidiobolae and Entomophthoromycosis Basidiobolae represent forms of zygomycosis (fungal diseases caused by zygomycetes).
Trichomycetes (Obligate commensals of arthropods) - refer to pages 96-101 in the textbook.
- 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.
Figure A: "Trichospores" - one-spored sporangia.
Figure B: "Zygospores" - one-spored zygosporangia
Figure C: A zygospore - a one-spored zygosporangium
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