ZYGOMYCETES I
PLANT BIOLOGY 371
GENERAL MYCOLOGY
LECTURE 27
4 DECEMBER 2003

Kingdom - Mycota

Phylum - Zygomycota

Class 1 - Zygomycetes - ~ 867 species
in 125 genera, 30 families and 7 or 10
orders.

Class 2 - Trichomycetes - 189 species in
48 genera, 7 families and 4 orders.
ZYGOMYCOTA

DISTINGUISHING FEATURES:

SEXUAL SPORE = ZYGOSPORE

ASEXUAL SPORE = NON-MOTILE
SPORANGIOSPORES
ZYGOMYCOTA

No motile cells
 Hyphae without septa
 Cell walls contain chitin
 Asexual spores formed in sporangia (except
Trichomycetes)
 Sexual spore (zygospore) formed by
gametangial fusion
 Life cycle is haploid with restricted diploid
ZYGOMYCETES


1818 - Christian Gottfried Ehrenberg named a
new genus (a fungus he found growing on the
cap of Agaricus aurantius) as Syzgites
megalocarpus.
1820 - Ehrenberg described the stages by
which conjugation of 2 filaments occurred and
a black fruit body was formed. He regarded
this as a sexual process similar to the one that
occurred in the alga, Spirogyra.
ZYGOSPORE

1864-81 - de Bary (deBary & Woronin) reexamined S. megalocarpus and emphasized the
sexual nature of the conjugation and named the
fusion spore a zygospore (zygos = yoke, spora
= seed; spore). Two years later, they described
the zygospore in R. stolonifera.
ZYGOSPORE
ZYGOMYCOTA

Saprobes of dead plant and animal material,
mostly in terrestrial habitats although they can
be isolated from water.

Some pathogenic species on humans and other
animals, especially invertebrates.

Some species symbiotic with invertebrates or
plants.

Several commercially important species.
BASIC LIFE CYCLE
Rhizopus sp.
ASEXUAL REPRODUCTION

Non-motile, spores are cleaved out of cytoplasm
within a multinucleate sporangium.

Each sporangiospore consists of a haploid nucleus,
cytoplasm, organelles and a cell membrane and
cell wall.

Spores are resistant to unfavorable environmental
conditions and allow for dispersal over distance
and time.
ASEXUAL REPRODUCTION

The form of the sporangium can vary
considerably among taxa.

Because many zygomycete species have not
been observed to reproduce sexually or do so
within a rather narrow range of environmental
conditions or only when the appropriate
mating strains are present, asexual
reproductive morphology is used to identify
taxa.
ASEXUAL REPRODUCTION
From K. L.
O’Donnell, 1979
ASEXUAL REPRODUCTION
From K. L.
O’Donnell, 1979
ASEXUAL
REPRODUCTION
ASEXUAL REPRODUCTION

Stolons

Rhizoids

Sporangiophores

Columella

Sporangia

Sporangiola

Merosporangia

Unispored sporangiola
From K. L.
O’Donnell,
1979
Columellate Sporangium
From K. L. O’Donnell, 1979
Columellate Sporangium
From K. L. O’Donnell, 1979
Sporangium with Persistent Wall
From K. L.
O’Donnell,
1979
SPORANGIA & SPORANGIOLA
From K. L.
O’Donnell, 1979
MEROSPORANGIA
From K. L.
O’Donnell,
1979
UNISPORED SPORANGIA
From K. L.
O’Donnell,
1979
SEXUAL REPRODUCTION
Zygospore
types from K. L.
O’Donnell,
1979
MUCORALES

Asexual reproduction by multi-spored
or few- (to one) spored sporangia
(sporangiola).
 Sexual reproduction by zygospores.
 Cosmopolitan saprobes.
 A few facultative parasites of plants or
animals (including humans.
MUCORALES

Contains commercially important species synthesize certain organic acids (citric, succinic,
oxalic, fumaric, lactic), unusual alcohols, -carotene,
transform steroids from one form to another (R.
arrhizus/progesterone), etc.
 Some species (eg. Rhizopus stolonifera) attack fruits
and vegetables in transit or storage (strawberry leak,
soft rot of sweet potatoes)
 Cause mucormycoses in humans (Rhizopus arrhizus,
R. oryzae, species of Mucor, Rhizomucor, Absidia,
Cunninghamella) - four kinds of systemic infection:
rhinocerebral, thoracic, gastro-intestinal, and
cutaneous. Some species also cause abortion in
cattle and swine.
MUCORALES

Most mucors are mesophilic. Two species, M. miehei
& M. pusillus, however, are thermophilic, i.e., they
grow best at 50 C or above and will not grow below
20C.

Thermophilic fungi are important decomposers in
insulated piles of plant debris such as composts, hay
and grass piles, peat, herbivore dung. Unfortunately
both thermophilic mucors have been reported as
causative agents of animal mycoses which limits their
use as rapid decomposers.
MUCORALES

In some countries, species of Mucor and Rhizopus are
used in the production of alcohol (e.g., Sake) from
grain mash. Corn mash is cooked to 40 C and cooled
and inoculated with fungus. The mash is cooled to 32
C and yeast is added. The Mucors break down the
starch (amylase) to simple sugars which are then
utilized by yeast to produce alcohol. Fungal amylase
is more efficient in converting starch to simple sugars
than germinating malt seedlings, which are used in
this country.
MUCORALES

Tempeh, a kind of soybean cheese which is an
important food in Indonesia, is made by
inoculating cooked soybeans with Rhizopus
oligosporus. The fungus helps digest the
protein and imparts flavor. The same type of
food is made in China but it is called sufu and
the fungus is Actinomucor elegans.
FAMOUS MUCORALES

Pilobolus (hat-thrower, cannon ball or shotgun fungus.

Spores are forcibly discharged as a single
unit in the sporangium.

Sporangiophores are positively phototropic.
(Why?)

Fungus exhibits a biorhythm in spore
formation and discharge.
PILOBOLUS
zygospore
From
K.L.
O’Donnell
Sporangium &
sporangiophore
From C.T. Ingold, 1971
From C.T. Ingold, 1971
SPORANGIOSPORE
DISPERSAL
 Wind
 In
sticky material
 Active discharge