Protozoa—Microorganisms Found in
All Soils

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Protozoa are a major part of all living soils.

They're single-celled organisms that feed on bacteria, other protozoa, organic matter, and sometimes fungi. They are several times larger than bacteria. The numbers of protozoa in the soil vary – from 1,000 per teaspoon in infertile soils to 1,000,000 per teaspoon in some fertile soils.

Three Protozoa Groups Based on Their Shape

Ciliates

Ciliates are the largest of the protozoa.

They move rapidly through the soil by means of hair-like cilia.

They eat the other two types of protozoa, also bacteria.

They consume up to 10,000 bacteria per day, and make nitrogen available to plants.

Ciliates are the least numerous of the 3 groups.

Amoebae

Amoebae (also spelled amebae by some people) can be large. They move by means of an appendage called a pseudopod.

Amoebae are divided into testate amoebae and naked amoebae.

One group of amoebae eat fungi and root pathogens.

Flagellates

Flagellates are the smallest of the protozoa. They use whip-like flagella to propel or pull their way through soil.

Functions of Protozoa

Protozoa help make nutrients available to plants and other soil organisms.

They regulate bacteria populations by grazing on them. This consumption seems to stimulate growth of those bacterial population. They're a food source for other soil organisms. They also help to suppress disease by feeding on pathogens.

Where Will I Find Protozoa?

Protozoa need water in which to move, which plays a big role in determining which types of protozoa will be present in your gardens.

They're are particularly active next to roots.

Fungal-infested soils, like forests, have more testate amoebae and ciliates. In bacterial-infested soils, flagellates and naked amoebae dominate.

High clay soils contain a higher number of flagellates and naked amoebae.

From Protozoa to Soil Microorganisms