Phylum Zygomycota

I. Class Zygomycetes. (115(+60) gen., ~665 Sp.

A. Group characteristics

1. Wall generally chitin with chitosan matrix (*1*4 homopolymer of N-acetyl

glucosamine; partially deacylated chitin) though *1*3 glucans present is some

groups or structures

2. Thallus often coenocytic, but may be regularly or irregularly septate,

haplobiontic, haploid

3. Sexual reproduction via zygospores produced in a zygosporangium as the result

of gamatangial fusion

4. Asexual reproduction generally by aplanospores produced in a sporangium

(i.e. sporangiospores not conidia), other spore types, (i.e. chlamydospores,

arthrospores) may also be present

B. Ecological roles - members of the group carry out all imaginable ecological roles and

include a variety of the "unique" ecologies associated with fungi

1. saprophytes, both in natural environments and as "spoilage" organisms

2. parasites of animals, especially insects (Entomophthorales)

3. parasites of plants

4. animal "predators" (Zoopagales)

5. mycorrhizal symbionts (Endogenales)

C. Taxonomy - Variously divided into Orders based largely on growth habit and somatic

structures

1. Three Order System Mucorales, Entomophthorales, Zoopagales

2. 6 or 7 or 8 Order system, (book uses 7) elevates the Dimargaritales, Kickxellales

Endogonales and Glomales from families in the Mucorales largely due to the

presence of either regularly or irregularly septate mycelium (Dimargaritales,

Kickxellales) or specialized habit (Endogonales, Glomales)

II. Mucorales - Largest Order - 49gen, 170 sp., largely saprophytes, rare mycoparasites and

occasional opportunistic parasites of plants and animals (including mucormycoses of man)

A. Somatic structures

1. Well developed mycelium generally aseptate, rhizoids may be present connected

by stolons (see Rhizopus stolonifer

2. Some species (see Mucor) may shift between a hyphal thallus and a single

cell/budding yeast thallus (are dimorphic) depending on O2/CO2 concentrations

B. Sexual reproduction - Zygospores

1. Gamatangial fusion of specialized gametangial branches which may be relatively

simple and equal in size or more complex and unequal

2. Basic Pattern

a. multinucleate progamatangia are produced (may be formed on

specialized hyphae called zygophors)

b. progamatangia (usually of different mating types with trisporic acids as

pheromones) match up and are separated by a fusion septum

c. progamitangium split by gamatangial septum into a gamatangium and a

suspensor cell.

d. Fusion septum dissolves and plasmogamy and eventually karyogamy

takes place forming a prozygosporangium

e. prozygosporangium thickens and is often armored to form the

zygosporangium, meanwhile a single, diploid zygospore develops

f. germination (along with meiosis) follows a dormant period, usually to

form an asexual sporangium

C. Asexual Reproduction

1. general case is aplanospores produced in a sporangium born on a sporangiophore

2. the variety of patterns possible

a. sporangia can be relatively large, many spored structures = sporangium

b. can be a small structure with only a few spores (as few as 1) =

sporangiolum

c. when a sporangiolum is cylindrical it is called a merosporangium

d. sporangiola can be born on swollen sporangiophores directly or on little

pegs

e. one species can produce both sporangia and sporangiola. the production

may be temporal or nutritional but you can get simultaneous production,

even on the same sporangiophore

f. sporangiola may be borne on specialized branches that come off the

sporangiophore = sporocladium

g. the sporangiophore may have specialized parts such as the trophocyst

and sub-sporangial vesicle of the Pilobolaceae

h. the spores produced are sporangiospores not conidia as evidenced by the

spore wall/sporangiolum wall sandwich

3 division of the order into families and genera is largely based on sporangiophore/

sporangium/ spore morphology

III. Order Dimargaritales -

A. 1 fam 4 gen., 14 ssp

B. Group separated out on the uniform production of 2 spored merosporangiola and

regularly septate hyphae with unusual septa

IV. Kickxellales

A. 1 fam. 8 genera 21 ssp

B. septate mycelium with a plugged perforation and the sporangiola bearing 1 spore

separate the group

V. Endogonales

A. produce sporocarps, usually below ground. These sporocarps contain zygospores,

B. Zygospore formation in the usual way in Endogone only

VI. Glomales

A. group of endomycorrhizal fungi, old term VAM (vesicular arbuscular mycorrhizal)

current AMF (arbuscular mycorrhizal). Obligate biotrophs

1. with a variety of hosts which span the vascular plant kingdom from

pteridophytes to grasses Some reports from mosses

2. plants can be experimentally infected by adding a variety of spore types to soil

with an appropriate host.

3. it is not clear if all the morphologically related mycelium in roots are genuinely

members of the Glomales because you can't culture them outside the roots but

genetic fingerprints suggest it

B. Often go unnoticed because the often do not result in any gross morphological change in

the root

C. Plants contribute CH20 to fungus via arbuscules

D. AMF serve as "extended roots" in P, N and water nutrition

E. azygospore - 6 layered walled spore formed with both chitin and cellulose

VII. Zoopagales

A. 14 gen. 144 ssp of predacious or parasitic zygomycetes, sticky-trap types

B. mycelium starts out aseptate but septates with age, zygospores produced wherever sex

has been seen, spores "conidia-like and usually sticky

IX. Entomophthorales

A. 2 fam. 20 gen. largely parasites, esp. of insects, also plants, algae, mosses, and some

saprophytes

B .mycelium not extensive, coenocytic and usually fragmenting into hyphal bodies, may

produce sticky rhizoids that attach the dead insect to a substratum

C. azygospores( not necessarily like Endogonales and sometimes called resting spores

produced in some cases

D. zygosporogenesis results from gamatangial contact, often of unequal size gametangia

with the zygospore coming off laterally or from the larger gamatangium

E. Chitin surrounded by B-glucan similar to chytrids, not rest of zygomycetes

VIII. Origins - 2 camps

A. Mucorales general in structure, non-parasitic and various, serve as stem and other orders

arose by modification

B. Endogonales linker group from chytrids (loss of flagella) to ascomycetes and stem of

other zygomycetes

X. Class Trichomycetes - all arthropod symbionts (4 orders, 7 fam. 38 gen. 136 ssp)

A. thallus simple or branched, septate by pore/plug type septa held to substratum by a hold-

fast

B. zygospore produced in only one of the 4 orders (Harpellales)

C. Wall material and septation differs among the orders,

1. 2 appear to be allied with the Kickxellales (Harpellales and Asellariales)

2. Eccrinales are cellulosic

3. Amoebidiales contain galactose/galactosamine (like the thraustochytridaceae and

myxomycetes)

D. Asexual spores vary by order,

1. trichospores in Harpellales

2. arthrospores in the Aselariales

3. sporangiospores in the Eccrinales

4. amoeboid in the Amoebidiales

E. Phylogeny of the Trichomycetes

1. probably not monophyletic

2. Harpellales and Aselariales probably with Zygomycetes (associated with

Kickxellales)

3. Eccrinales, perhaps of Algal origin or "phycomycete" origin

4. Amoebidiales - protistan

Zygomycetes 3