The Fungus-like Protists
Dog vomit slime mold
Characteristics
• The Fungus-like protists are heterotrophs that
absorb nutrients from dead or decaying matter.
• They play a key role in recycling organic material.
• The difference between them and true fungi is that
unlike fungi they have centrioles, but lack the chitin
of fungal cell walls.
Types of Fungus-like Protists
• cellular slime molds
(Phylum Acrasiomycota)
• acellular slime molds
(Phylum Myxomycota)
• water molds
(Phylum Oomycota)
Water mold breakdown
of a fish
Slime Molds
They are found in damp places rich in
organic matter, such as forest floors,
or on compost.
Cellular slime molds (Phylum
Acrasiomycota)
They are made up of distinct individual cells
separated by cell membranes during every
phase of the mold’s life. They spend most
of their lives as free-living cells that are not
easily distinguishable from soil amoebas.
• When their food supplies are exhausted,
they send out chemical signals that cause
the cells to aggregate into a slug-like
colony that begins to function as a single
organism.
• Eventually it becomes a reproductive “fruiting
body” that produces spores, which eventually
become single amoebae.
• During much of their life cycle, the cellular slime
molds look and behave like animal-like protists.
When they aggregate, however, they act very
much like multicellular organisms.
Acellular slime molds (Phylum
Myxomycota)
They begin their life cycle as amoeba-like cells,
that eventually fuse to produce a structure with
many nuclei. These structures are known as
plasmodia (singular = plasmodium). The
plasmodium may grow several meters in
diameter.
• Eventually fruiting bodies called sporangia
spring up from the plasmodium to produce
haploid spores by meiosis.
The spores scatter to the ground and
germinate into flagellated cells, which fuse
to produce diploid zygotes to repeat the
cycle.
Water molds (Phylum Oomycota)
• If you’ve seen white fuzz growing on a
dead fish in the water, it is a water mold
in action.
• The water molds thrive on dead or decaying
organic matter in water, and are plant parasites
on land.
• They produce fungal-like filaments called
hyphae. They have cell walls made of cellulose,
which is different from a fungus.
• They can produce flagellated spores which
swim away in search of food. When they
find food they grow hyphae into new
organisms.
THE IRISH POTATO FAMINE OF THE 1840s
One water mold, Phytophthora infestans, that produces airborne
spores, can destroy all parts of a potato plant. The infected
potatoes appear normal at harvest time, but within a few weeks
it is reduced to a sponge sac of spores and dust.
In Ireland, the summer of
1845 made ideal growing
conditions for the fungus
(unusually cool and wet).
By the end of the growing
season, the potato blight
had destroyed 60% of
the potato crop.
• The Great Potato Famine or “Great
Hunger” led to starvation of more
than a million people and the mass
migration of 1.5 million to the
United States.