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The Ecology of Ciliated Protozoa

Jack Dazley is primarily a researcher in environmental science and biology.

The great diversity of ciliates found globally (Finlay 1997)

The great diversity of ciliates found globally (Finlay 1997)

What are Ciliated Protozoa?

Ciliates are microscopic, single celled organisms which are named for the abundance of tiny hairs (cilia) on the cell surface. They have been around for over 500 million years, and play a crucial role in maintaining water quality, as they feed on bacteria in the water. They are incredibly diverse organisms, and are found all over the world in habitats such as soils, freshwater, marine environments and even snow.

Ciliate Ecology

Most ciliates are described as phagotrophic, in that they feed on other organisms and cannot photosynthesize. There are some exceptions to this however, with some species such as Paramecium bursaria (pictured below) having endosymbiotic algae which live inside the cells. These organisms can be described as mixotrophic, because they can photosynthesize using the algae inside the cell, but can also feed on other organisms.

The ciliate Paramecium bursaria with endosymbiotic algae

The ciliate Paramecium bursaria with endosymbiotic algae

Ciliates feed on a wide variety of microbes, including bacteria, algae, flagellates (small single celled organisms with a tail-like flagellum) and even other ciliates. Indeed some larger have been species have been observed feeding on small animals such as rotifers! Ciliates are in turn also fed upon by zooplankton such as water fleas and copepods. Small fish feed on these zooplankton and essentially ciliates link microbial food webs with macroscopic food networks (involving invertebrates, fish, etc.)

Ciliates are also involved in nutrient cycling within the microbial loop. As ciliates feed on bacteria and algae, the organic matter accumulated by these organisms is passed up the food web, to larger organisms such as fish. However, when ciliate cells die, they release the organic matter accumulated through feeding and this is taken up by bacteria. A schematic representation of this is shown below:

The microbial loop in a typical aquatic ecosystem, showing bacteria being fed on by ciliates and other protozoa, which are in turn eaten by zooplankton

The microbial loop in a typical aquatic ecosystem, showing bacteria being fed on by ciliates and other protozoa, which are in turn eaten by zooplankton

Applications of Ciliates in Sewage Treatment Plants

Stalked ciliates such as Epistylis sp. are commonly used in wastewater treatment plants in order to clean sewage water. These ciliates feed on the bacteria and as such they help to clean up the water. In this sense, ciliates can also be used as indicators of water quality in natural bodies of water, such as rivers and lakes.

Ciliates found in wastewater include stalked species such as Epistylis, which feed on bacteria in the water

Ciliates found in wastewater include stalked species such as Epistylis, which feed on bacteria in the water

Conclusion

Overall, ciliates, despite their tiny size, play a significant role in the healthy functioning of aquatic ecosystems, by keeping blooms of bacteria and algae under control, and as such maintaining water quality. They also are fundamental in nutrient cycling in freshwater ecosystems, and as a key component of the microbial loop.

Comments

Louise Powles from Norfolk, England on March 23, 2018:

I learned something new today. I didn't know anything about ciliates till reading this.