The Fungus-like ProtistsDog 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.