Station 2: Kingdom Fungi - Phylum Chytridiomycota

Phylum Chytridiomycota (Chytrids)

Chytridiomycota, commonly called chytrids, represent one of the earliest-diverging groups of fungi. Most chytrids are microscopic and live in aquatic environments or moist soils.

Unlike most other fungi, chytrids produce flagellated reproductive cells called zoospores. These spores are capable of swimming through water using a single flagellum.

Because their spores require water for movement, chytrids are most commonly found in environments such as ponds, wetlands, and damp soils.

Some chytrids function as decomposers, breaking down organic material in aquatic ecosystems, while others live as parasites of algae, plants, insects, or amphibians.

The Defining Feature of Chytris

The most distinctive characteristic of chytrid fungi is the production of zoospores.

Zoospores are spores that possess a single posterior flagellum, allowing them to swim through water. This feature distinguishes chytrids from all other fungal groups, whose spores are non-motile.

The presence of motile spores reflects the evolutionary history of chytrids and explains why these fungi are typically associated with aquatic or very moist environments.

Micrograph showing several chytrid zoospores, each possessing a single posterior flagellum used for swimming. These motile spores are characteristic of fungi in the phylum Chytridiomycota and distinguish them from all other fungal groups, whose spores are non-motile.

Zoospore release and motility in Allomyces.

This video shows zoospores being released from a sporangium of the chytrid fungus Allomyces. Each zoospore possesses a single posterior flagellum that allows it to swim through water. Watch only the first minute of the video, which shows the release of zoospores and their movement away from the sporangium.

Observing a Chytrid: Genus Allomyces

In this lab you will examine Allomyces, a genus of chytrid fungi that is commonly used in teaching laboratories.

Allomyces forms simple filamentous structures and produces sporangia that release spores. While this organism has a complex life cycle, you are not expected to memorize all stages of reproduction.

Instead, the purpose of observing Allomyces is to recognize the basic structure of a chytrid fungus and understand that members of this group produce motile zoospores.

Basic Structure of Allomyces

The body of Allomyces consists of thin filaments called hyphae. A network of hyphae forms the mycelium, which is the main body of the fungus.

The hyphae are surrounded by cell walls made primarily of chitin, a structural polymer also found in the exoskeletons of arthropods.

At the tips of some hyphae you may observe sporangia, which are specialized structures that produce spores. These spores may eventually develop into new fungal individuals.

This is an image of an Allomyces diploid phase (called a sporophyte, a botanical term holdover).

Lab Activity: Observing Allomyces

Materials

Prepared slide of Allomyces
Compound light microscope
Lens paper

Note: Handle prepared slides carefully, as they are made of glass and can break if dropped or handled roughly. If a slide breaks, notify your instructor and do not attempt to clean it up yourself.

Instructions

Place the prepared Allomyces slide on the microscope stage and bring the specimen into focus.
Scan the slide to locate regions containing filamentous hyphae, which make up the body of the fungus.
Look for sporangia, which appear as swollen or rounded structures attached to the hyphae. These structures produce spores.
Examine several different areas of the slide to observe variation in the structures present.
Compare what you observe on the slide with the images shown on this page.

Clean Up

Remove the slide from the microscope and return it to the slide tray.
Return the microscope to its storage location as directed by your instructor.
Clean the work area if necessary before moving to the next station.

Chytrid Infection in Amphibians

Some chytrid fungi are parasites of amphibians. One species, Batrachochytrium dendrobatidis, causes a disease known as chytridiomycosis.

This fungus infects the skin of amphibians. Because amphibian skin plays an important role in respiration and water balance, infection can disrupt these functions and may lead to death.

Chytridiomycosis has been associated with major declines in amphibian populations around the world.

A microscopic image of A zoospore of Batrachochytrium dendrobatidis. This is the infection agent that once released from the skin of a frog can infect other frogs.

A zoospore of Batrachochytrium dendrobatidis. This is the infection agent that once released from the skin of a frog can infect other frogs.

This is a section through frog skin with the chytrid infection. the arrows on the image are highlighting the zoospores being release on the surface of the skin.

An image of a frog killed by chytrid fungus. The legs are discolored yellow to red indicating the infection.

This infection is also referred to as "yellow-legs" because it often turns the legs yellow to red. This chytrid has been known to cause massive decline in frog populations and may be responsible for several extinctions. Frogs are particularly susceptible because as an aquatic creature lacking many of the protective skin structures (like scales) live in the very habitat that most chytrids prefer.

This video is about how to treat Chytridiomycosis and has some good images of the zoospores.

Key Concept

Chytrids are the only fungi that produce flagellated zoospores capable of swimming through water.

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