Powerful Protozoans

This appeared in the January 13, 2021 edition of The Fish Wrap.

We continue our exploration of the soil food web with two movers and shakers of the protozoan family - ciliates and flagellates. Every farmer should have a microscope because recognizing the density of these creatures in your soil can tell you a lot about its condition and what will support it best. If you see ciliates (recognizable by legs around their perimeter) it could mean the soil is becoming anaerobic, or waterlogged. Ciliates prefer eating anaerobic bacteria. If flagellates (recognizable by a single whip-like leg) dominate, and amoeba are low, it could mean an imbalance in nutrient cycling, leading to an overgrowth of undesirable plants.

Protozoa are single-celled animals that feed primarily on bacteria, but also eat other protozoa, organic matter and fungi. By eating bacteria, they release nitrogen and other nutrients that can be used by plants and other players in the soil food web. Ciliates are the largest protozoa, using their hair-like cilia to scoot around gobbling up bacteria and other protozoans. Flagellates are the smallest, whipping themselves around to eat the smaller bacteria. Both help regulate bacteria populations, feed on pathogens to suppress disease and generally play a key role in maintaining the delicate balance of a healthy soil food web.

Carnivorous ciliates consume up to ten thousand bacteria per day. They have various organelles including a mouth, but they rely on their cilia for everything including swimming, crawling, attachment, feeding and sensation. Cilia are hair-like projections that have musculature used for locomotion as well as sensory cells which receive and respond to information from the surrounding environment.

Flagellates are the smallest protozoan, but with their whip-like tails, they really get around! Their flagella can be used to propel or pull them through soil, and to create a current that flows food into their mouths for filter feeding.