The Secret Life of Bugs:

Stalked Ciliates Contracting

by Natalie Walton, Aquafix Microscopist

If you have read the stalked ciliate entry in our microorganism database, you know they have an inverted bell-shaped head called a zooid, come in a variety of sizes, and fall into one of two distinct groups: those with a lorica (a shell) and those without. The database even touches on how both types have the ability to contract. But why do these organisms contract? While contractions are often associated with birth, that is not the case for stalked ciliates; they are a single-celled organism that doesn’t reproduce like a human, or rotifer, for that matter. But before we dive into the “Why?” of contractions, let’s start with the “How?”.

Stalked ciliates attach themselves to floc with a stalk that contains a coiled fiber called a spasmoneme (or myoneme). Approximately 40-60% of the spasmoneme dry weight comes from a calcium-binding protein called spasmin. In response to external stimuli or at spontaneous intervals, calcium is released from the cell body. This calcium then binds to the spasmin, inducing tension in the spasmoneme and thus causing a contraction. Since the spasmoneme is coiled up in the stalk in a helical way, this causes the stalks to contract into a spiral/spring-like shape, such as in the video. Once the calcium begins to dissipate, the spasmoeneme begins to relax and thus uncoil.

However, not all stalked ciliates contract in the same way. In colonies, some stalked ciliates can contract individually while others can only do so simultaneously. This is species-dependent. In some species, each stalk has its own spasmoneme and thus can contract independently from the group. Other species have a shared spasmoneme that connects all of the stalks together; thus, they can only contract simultaneously.

You may be thinking, “Wow, that’s pretty cool information, but why should I care about stalked ciliates and their contractions? I’m not on a trivia team.” Well, my dear reader, the answer to that brings us to the earlier question of why stalked ciliates contract.

There are multiple reasons why stalked ciliates contract. The first being that contracting helps to protect the stalked ciliates from predators and other fluctuations within a plant. The activated sludge system is full of turbulence, collisions, and metazoa/larger protozoa that graze on smaller organisms. So, by pulling their body down towards floc, the stalked ciliates reduce their exposure and minimize damage, thus increasing their survival rate.

Secondly, contracting plays a part in how stalked ciliates eat. Stalked ciliates create a whirlpool-like current with the cilia surrounding their mouth to bring free bacteria within reach. After a sufficient amount of food has collected, stalked ciliates will then contract to push the food into their bodies, where the free bacteria are then enclosed in a food vacuole for digestion.

The final reason stalked ciliates contract may be the simplest – it just randomly happens. While stalked ciliates typically contract for a reason, sometimes it just happens without cause. This is similar to when you or I suddenly get a muscle spasm that comes as quickly as it goes.

Now that we know how and why stalked ciliates contract, this knowledge can be applied to elevate day-to-day diagnostics. Once a microbial baseline has been established through daily microscopy observations, you can monitor for changes in how stalked ciliates contract. For example, if they suddenly start contracting sluggishly or not at all, it could be an indication that there is an issue, such as low dissolved oxygen or toxicity occurring. However, if the stalked ciliates are contracting vigorously, the microbial community is likely healthy. But, as with most indicators in wastewater, they alone do not indicate a problem. Multiple indicators need to be present, and many factors should be considered before definitely determining if a problem is present.

Ultimately, stalked ciliates contracting is more than just a mini microscopic fireworks display; it is a survival strategy. By watching how these organisms behave, not only will you appreciate their intricacies a little more, but they also may provide you with clues as to the health of your system.

Thanks for reading and stay tuned for the next edition of Secret Life of Bugs.

Have something under the microscope you don’t quite understand? Try our Microanalysis and Filament Origins Test Kit to get a comprehensive view of what is happening in your plant.

About the Author

Natalie Walton joined Aquafix in 2019 and focuses on performing microscopic analysis for customer samples, as well as conducting experiments on innovation in grease removal. She was also a key contributor to creating our Microorganisms Database supplying identification tips and research.