Among the many organisms on Earth, the protists are perhaps the most difficult to characterize because of their differences. Of the protists, Euglena green algae are intriguing scientifically, yet sometimes troubling for property owners. The movements and dietary habits of Euglena are fascinating.
TL;DR (Too Long; Didn't Read)
Euglena, or green algae, are unicellular, microscopic protists. They alter their dietary needs based on their environment, and they have unique ways to expel excess fluids and waste.
What Is Euglena?
Euglena is the genus name for a set of microscopic organisms. They were first revealed in the 1800s under a microscope, where their structures and movements could be easily observed. They are a kind of protist, which is a sort of umbrella term for eukaryotes that cannot be classified as plant, fungus or animal.
Euglena is just one of at least 100,000 kinds of protists known thus far. Euglena often lives in ponds or other bodies of fresh water and is also known as green algae. Each Euglena cell is a whole, single-celled organism with unique features.
Characteristics of Euglena
The Euglena cell is an active, hardy little single-celled organism on the move. They are microscopic, meaning one needs a microscope in order to view them. Their presence is obvious on a large scale during an algal bloom, however. Euglena characteristics prove there is more to this little unicellular creature than meets the eye.
Euglena green algae are oblong and usually green. The front of a Euglena cell is narrower than its rear. Each Euglena cell possesses a little red eyespot. The Euglena also boasts a flagellum tail. Euglena constantly moves to find the best light.
An interlocking protein coat called a pellicle surrounds the Euglena cell. This pellicle serves as defense for the little protist. It keeps the cell from becoming damaged while allowing it to continue to move. It also works as a shield against sunlight. Once sunlight strikes Euglena, the cell will transform from its green state to red, closing it off from the fierce sun.
Euglena reproduces via asexual reproduction. This process yields two daughter cells and is called binary fission.
How Does Euglena Move?
A Euglena cell’s motility derives from its whippy tail-like appendage, called a flagellum. Euglena uses this tail as it makes its way through fluids searching for food, or when it wants to change direction.
Much of the time, the Euglena cell swims through water in a spiraling movement. Its flagellum pulls it forward. Euglena generally streaks along a straight path. It can roll on its axis as well so that its eyespot gets a good exposure to light.
But occasionally, Euglena needs to change direction. So to stop moving forward, they can actually change shape!
This recent discovery revealed that Euglena could morph into intricate shapes, specifically polygons, from triangles to pentagons. Scientists discovered that Euglena performs this transformation when exposed to varying light levels. The movement of Euglena toward light is called phototaxis.
When Euglena encounters strong light with its eyespot, it makes brisk turns that turn it into a triangular shape. It continues bending until it makes a many-sided shape, and then eventually it can straighten out again. Scientists think Euglena uses this shape-shifting skill to navigate environments like ponds, which have varying degrees of shade and sunlight. This is another protective mechanism for Euglena to avoid sun damage.
How Does Euglena Eat?
One really of the interesting Euglena characteristics is its ability to switch up its mode of eating. It is considered to be a mixotroph.
Euglena uses photosynthesis to make food as if it were a plant. It does this under conditions of adequate sunlight. In this regard, it behaves as a photoautotroph.
When sunlight is not readily available, the Euglena cell behaves more like an animal, moving around and hunting for food. Therefore, Euglena also behaves like a heterotroph when the need arises.
Heterotrophic protists take in food they find via phagocytosis. Their membranes surround food and pinch it inward into a little sac or food vacuole.
How Does Euglena Expel Waste?
The little food vacuole, or phagosome, combines with an enzyme and becomes a phagolysosome. After Euglena cells take in their food, the nutrients from the food are absorbed and used for metabolic purposes to keep the cell alive. Anything that does not get used by the Euglena cell gets expelled.
The term for getting rid of Euglena excretion in this manner is called exocytosis. Waste materials that are water soluble, like ammonia, must be removed so as not to build up inside the Euglena cell.
All waste material that Euglena cannot digest first bonds with the cell’s membrane by way of the contractile vacuole. This organelle is not used for storing any food. The contractile vacuole serves as an organelle responsible for removing waste.
It helps keep the Euglena cell from bursting from excess water as well. The process that keeps fluid levels balanced in the Euglena cell is called osmoregulation.
When it is time to remove excess water, the vacuole fuses with the Euglena cell membrane, contracts and expunges the water outside the cell. Contractile vacuoles work to collect water, in the diastole phase. The removal of waste by the contractile vacuole is named the systole phase. Contractile vacuoles are common among unicellular protists.
Challenges for Dealing With Euglena
While Euglena is not a pathogenic micro-organism toward humans, it presents issues for homeowners with ponds or boats. This is because of its tendency to change color. When a pond changes from green to a brilliant, staining red, it is apparent that Euglena green algae are at work.
What happens to these creatures that makes them turn from green to red? As mentioned previously, they have a shell-like covering called a pellicle. Unique among Euglena characteristics, the organism, when exposed to strong sunlight, secretes a substance to make the pellicle harder. This makes a nice sunscreen for the little protist. It also makes the Euglena shell a brilliant red in hue.
This transformation can occur very quickly, even under 10 minutes. While colorful to look at, typically homeowners do not desire a pond or lake riddled with red algae. It might be tempting for a homeowner to cover a pond to try to quell the expansion of the bloom. However, Euglena adapts to such changes like a champ.
While Euglena usually undergoes photosynthesis, it also eats other organisms. In addition to the undesirable color they give, these little Euglena cells zoom around gobbling up beneficial algae in the water as well. Once it infests a body of water, removal of red-hued Euglena becomes challenging. Their scarlet coats work so well against sun damage that they also repel algaecides.
For this reason, it is recommended to address Euglena populations while they are still green. That necessitates working in the morning before strong sunlight activates their pellicle shield; they are more vulnerable to algaecides in that state. Homeowners have to assess how best to remove Euglena before it becomes a problem while simultaneously fostering a healthy freshwater environment overall.
Big Ideas From Tiny Euglena
It is clear that little Euglena green algae are mighty survivors, adaptable to their surroundings. Scientists even think the unique movements of Euglena could inspire technological breakthroughs in making miniature robots that could potentially move inside the bloodstream of humans.
About the Author
J. Dianne Dotson is a science writer with a degree in zoology/ecology and evolutionary biology. She spent nine years working in laboratory and clinical research. A lifelong writer, Dianne is also a content manager and science fiction & fantasy novelist. Dianne features science as well as writing topics on her website, jdiannedotson.com.