Ciliates Microscopy – A Complete Guide Exploring Characteristics, Habitats and Reproduction

Ciliates are basically ciliated protozoans. Protozoans are another term for a group of single-celled eukaryotes. They are either parasitic or free-living and feed on organic matter such as debris, organic tissues, or other microorganisms.

Ciliates Microscopy - A Complete Guide Exploring Characteristics, Habitats and Reproduction

Because ciliates are ciliated protozoans, they are considered to be protists and belong to the “supergroup” Alveolata. Also in this super-group are apicomplexans and dinoflagellates. 

Ciliates are larger cells when you compare them to other single-celled organisms. Therefore, they feed on a range of microorganisms, including algae and bacteria.

Ciliates also have very short hair-like structures known as membranelles that they use for feeding as well as their cilia (translates as eyelash), which is used for movement. 

In the world of unicellular organisms, ciliates are considered to be some of the most complex. With such complexity comes intrigue. And, that intrigue has brought you here today.

In the following post, we will be discussing ciliates microscopy and exploring their characteristics, habitats, and reproduction cycle. We will start by finding out exactly what ciliates are.

What Are Ciliates?

Ciliates are essentially a group of alveolates. They are characterized by hair-like structures known as cilia. Upon closer inspection, these cilia hairs are almost identical to eukaryotic flagella.

However, cilia tend to be shorter and come in much larger numbers. Cilia also have a unique undulating pattern.

Ciliates are common around most places where there is a body of water. An important group of protists, ciliates are usually located in lakes, oceans, rivers, ponds, and soils.

It is believed that there are approximately 4,500 distinct free-living species, but experts are quite positive that the real number is estimated to be around 27,000 to 40,000.

This vast number includes many endosymbiotic and ectosymbiotic species. There are also believed to be obligate and opportunistic parasites, too.

As for the size of ciliate species, they can range from a little as 10 µm in various colpodeans to as large as 4 mm in length in some geleiids. Overall, they include some of the most complex protozoans in the world. 

Ciliates Characteristics

As we discussed above, ciliates are ciliated protozoa. This essentially means that they are a form of protozoa with hair-like organelles, known as cilia. These stem from the cell cortex. These hair-like projections are critical for the organism to help them move. 

Studies have found that cilia are also used by ciliates to crawl along surfaces, attaching to different items, and for sensation.

So, aside from helping the organism move from one place to another, cilia allows ciliates to sense any alterations in their environment. Therefore, they can react effectively to avert potential danger. 

As we mentioned earlier, cilia are more numerous and shorter than flagella present in other examples of single-celled organisms. In fact, cilia may actually cover the whole surface of an organism.

With so many cilia on their surface, ciliates are able to coordinate their movements very rapidly. 

Some organisms use cilia differently to others. Some, such as Aspidisca and Euplotes, use these hair-like structures to crawl, whereas others can swim in bodies of water. These are referred to as free-swimming ciliates, such as Paramecium. 

The Nuclei

In comparison to other single-celled organisms, ciliates are different in that they have two nuclei:

  • Micronucleus 
  • Larger macronucleus

The micronucleus contains two copies of each chromosome. Therefore, it is a diploid nucleus. The type of ciliate tends to determine whether there are one or multiple micronuclei in its single cell. 

The macronucleus is larger in comparison to a micronucleus. It also consists of shorter pieces of DNA. Typically, there are tens of thousands of copies.

When cell division occurs, the micronuclei usually undergoes mitosis, whereas the macronucleus is divided into two sections. 

Contractile Vacuole

Ciliates have a contractile vacuole. The job of this is to collect and remove water that has built up from the cell. If the concentration of a cell’s interior water molecules is high, they will begin to move to the contractile vacuole.

This always has a higher concentration of ions. Therefore, the water molecules are removed from the cell altogether.

This entire process means the cell can maintain ionic balance and osmotic pressure, as well as help prevent the cell from bursting because of the excess water within the cell. 

Oral Vacuole

Ciliates, such as paramecia, sport mouth-like features. These are known as an oral groove, and it is through these that they feed. Food particles are pushed through the cytopharynx (like a gullet) and then travel to the food vacuole.

This is where it is broken down.

Not all ciliates have an oral groove. Some use absorption to obtain nutrients and remain healthy. 

Habitats

Ciliates are divided into two categories:

  • Free living
  • Parasitic

Free living ciliates are those that can live outside a host and are found in just about any environment on Earth.

Parasitic ciliates always live in the body of their hosts.

An example of a free living ciliate is Paramecium. These can be found free living in fresh bodies of water, where they can feed on different types of bacteria. 

Ciliates Microscopy - A Complete Guide Exploring Characteristics, Habitats and Reproduction (1)

An example of a parasitic ciliate is Balantidium coli. This is found living inside humans (their host). Here, they live as endoparasites and can cause ciliary dysentery. 

Some ciliates, such as Paraenchelys terricola and Apospathidium terricola can also be found in soil. But, the soil concentration is determined by the amount of water found within the soil. Simply put, the higher the concentration of water found in soil, the more ciliates there will be. 

The concentration of ciliates will vary drastically depending on the conditions of their environment. So, how much water and nutrition is in the area will have a large impact on a ciliate population. 

Reproduction 

Ciliates can reproduce both sexually or asexually (conjugation or fission).

During sexual reproduction (conjugulation), a pair of ciliates with form a cytoplasmic bridge between them. After this occurs, meiosis of the micronuceli occurs with either cell. This produces haploid micronuclei.

Some haploid nuclei go through a disintegration process, while the remaining ciliates divide into two. This process is known as mitosis in both cells. One of the nuclei will then move to the other cell and form a diploid nucleus.

This then essentially builds a macronucleus, but only when the cells have separated. 

The next step in the process is the fission of the cell. This is while the macronucleus becomes divided into two separate parts and forms two daughter cells. Both of the daughter cells have a macronucleus and a micronucleus. 

So, basically, in the first phase of reproduction, the micromucleus of the cell goes through mitosis, whereas the macronucleus divides into two sections. This results in the cell dividing into two daughter cells. 

Cilia Feeding

The majority of ciliates are heterotrophs. They feed on smaller organisms, such as algae and bacteria. Also, detritus is swept into the mouth (oral groove) by modified oral cilia.

This process includes a number of membranelles on the left of the mouth and, to the right, a paroral membrane. Both of these come from polyketides.

These are large groups of cilia that stick together with associated structures. The Cilia then moves the food through the oral groove pore into the gullet of the ciliate, which forms food cavuoles. 

Not all ciliates feed in the same way, however. As we mentioned above, some ciliated are mouthless and feed through absorption. This is known as osmotrophy.

Others are predatory and will feed on other forms of protozoa, and, in some cases, they may feed on other ciliates. 

Various ciliates can also parasitize animals. But, Balantidium coli is the only known species that is known to cause diseases in humans. 

Ciliate Microscopy 

Ciliates, such as Paramecium, can be studied with just the use of a light microscope. To view these microscopic organisms, you can use a number of different techniques. 

Before you go ahead and start looking at ciliate under your microscope, there are a few important requirements:

  • A microscope (bright field, dark field, and phase contrast microscope)
  • A microscope glass slide
  • A microscope cover slip
  • A sample of Paramecium species
  • A dropper
  • Congo red dye
  • Vaseline
  • Spring water
  • Granular baker’s yeast 
  • Bunsen Burner
  • A spatula 

Ciliate Microscopy Techniques

Wet Mount

You can choose between two methods to prepare your wet mount for viewing ciliates under your microscope. You can either obtain a Paramecium species from pond water or even culture a sample to increase their overall number. 

The Hanging Drop Technique

This technique is probably the simplest and most straightforward method of preparing a ciliate sample to view under a microscope. All this technique involves is placing a water droplet on a cover slip.

The water droplet is suspended on the cover slip’s underside. This, in turn, is also placed over the cavity of the microscope’s glass slide. 

In this instance, the droplet of water stays suspended between the glass slide and cover slip. It is then viewed under the microscope with a high power. 

When researchers or students use this technique, they can see the microorganism moving quickly across their field of view, even though they are transparent. 

Paramecium are pretty large in comparison to other single-celled organisms. Therefore, they are more visible if you use a bright field microscope. 

Wet Mount Mixed With Stained Yeast

This technique sees users prepare a wet mount stand of their sample alongside stained yeast. This technique comes with a key benefit, especially when you compare it to other techniques.

If you use a wet mount stand with stained yeast, it can cause the Paramecium to slow down. Therefore, it becomes easier to view the microorganisms and identify different structures using the microscope. 

To use this technique, follow these steps:

  1. Take a spatula and place just a few grams of your baker’s years into a beaker.
  2. Add 100 ml of warm spring water. This will hydrate the yeast. 
  3. Now, add approximately 0.3 mg/ml of Congo red dye. Congo red dye serves as a pH indicator. The color will change from red to blue if the pH of the suspension changes from above 5 to below 3.
  4. Heat the suspension for around 10 or so minutes. Doing this will help reduce the suspension while the yeast concentrates. 
  5. Take a dropper and place just a small droplet of the sample that holds the concentrated paramecium. This should come into contact with the drop of stained yeast suspension. 
  6. Now, place a little bit of Vaseline onto the cover slip and carefully press your cover slip onto the glass slide. Using Vaseline allows for some of the air to be retained between the glass slide and cover slip. It also prevents the Paramecium from getting damaged.
  7. Finally, place the microscope glass slide under the bright field, dark field, or phase contrast microscope. This will allow you to compare how the Paramecium cells become visible. 

Dark field and phase contrast microscopes allow researchers to easily and clearly identify the cilia on both ends of the cells. They also allow users to view them close to the buccal cavity of the cells, too. This is not possible with a bright field microscope.

Whilst the two techniques we have discussed are very important for viewing cilia and other  cell organelles of an organism, a bright field microscope can allow you to identify the food vacuole of Paramecium more easily. 

In Summary

Ciliates are essentially protozoans that belong to the supergroup Alveolata alongside apicomplexans and dinoflagellates.

As they are larger cells than many other single-celled organisms, they tend to feed on other microorganisms such as algae and bacteria. 

Although some are microscopic, whilst others grow to up to 4 mm in length and can be seen with the naked eye, most require a microscope in order to study and see ciliates move around. 

Grab your microscope today and a small sample of pond water, and you will be able to study ciliates in all their glory yourself.

Jennifer Dawkins

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