6.5: Mold

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What's shrouding this dead insect?

The thin filaments growing out of this dead insect look a little like a fungus. Also this mystery organism, like a fungus, is feeding on decaying matter. However, this is not a fungus. This organism is a type of fungus-like protist, known as water mold.

Fungus-like Protists

Fungus-like protists share many features with fungi. Like fungi, they are heterotrophs, meaning they must obtain food outside themselves. They also have cell walls and reproduce by forming spores, just like fungi. Fungus-like protists usually do not move, but a few develop movement at some point in their lives. Two major types of fungus-like protists are slime molds and water molds.

Slime Molds

Slime molds usually measure about one or two centimeters, but a few slime molds are as big as several meters. They often have bright colors, such as a vibrant yellow (Figure below). Others are brown or white.

Stemonitis is a kind of slime mold which forms small brown bunches on the outside of rotting logs. Physarum polycephalum lives inside rotting logs and is a gooey mesh of yellow "threads" that are several centimeters long. Fuligo, sometimes called “vomit mold,” is a yellow slime mold found in decaying wood.

Water Molds

Water molds mostly live in water or moist soil. They can be parasites of plants and animals, getting their nutrients from these organisms and also from decaying organisms. They are a common problem for farmers since they cause a variety of plant diseases. One of the most famous of these diseases was the fungus that caused the Irish potato famine in the 1800s. At this time, potatoes were the main source of food for many of the Irish people. The failure of the potato crop meant that many people in Ireland died of starvation or migrated to other countries.

Summary

Slime molds are fungus-like protists that grow as slimy masses on decaying matter. They are commonly found on items such as rotting logs.
Water molds are fungus-like protists present in moist soil and surface water; they live as parasites or on decaying organisms.

Explore More

Use the resources below to answer the questions that follow.

Explore More I

The Blob: Slime Mold at blog.mycology.cornell.edu/2007/10/31/beware-the-slime-mold/.

Why are slime molds not classified as fungi?
What does a plasmodial slime mold eat?
What is different about the nucleus of the single cell of the plasmodial slime mold?

Explore More II

John Bonner's Slime Mold Movie at http://www.youtube.com/watch?v=bkVhLJLG7ug (1:42)

What happens when you separate the cells of a slime mold?
Do you think this behavior represents intelligence? Why or why not?
Slime molds will form stalks with fruiting bodies.
1. What happens to the cells of the stalk?
2. What happens to the cells of the fruiting body?

Review

What are examples of fungus-like protists?
How do water molds get their nutrients?