A scientist named Sebastian Hess recently discovered the tricks some amoebas use to eat. He studies eukaryotic microbes in Canada at Dalhousie University. Hess has loved watching tiny critters through a microscope since he was a kid. Ten years ago, Hess punched through the ice of a frozen pond in Germany. He collected a sample of water and took it back to his lab.
Through the microscope, he saw something odd. Green spheres were wiggling like tiny bubbles inside strands of green algae. So Hess mixed algae containing the green balls with other algae. The wiggling spheres popped out of the algae and started swimming. Shortly afterward, they invaded other algal strands. That means they can switch between two forms. In one form, they swim or glide using tail-like structures called flagella Fluh-JEH-luh. When the swimmers find food, they transform into amoebas.
Their shape becomes less rigid. Instead of swimming, they now begin crawling along some surface. Through the microscope, Hess watched one of these amoebas cut a hole in an algal cell. The amoeba squeezed inside. Afterward, the amoeba divided and made copies of itself. Those were the wiggling green spheres that Hess had seen earlier. The new amoebas punched more holes in the algal cell. Some invaded the neighboring cell in the algal strand.
Others escaped. He found a similar species in a bog. Instead, it cut a C-shaped gash in an algal cell. It gobbled up the material it pulled out of the cell. More recently, he discovered clues to how these two amoeboflagellates hack into algae.
Both seem to get help from a protein called actin AK-tin. Human cells use the same protein to move. In amoeboflagellates, actin forms a mesh. It helps the cell make a pseudopod. The mesh might also help the pseudopod latch onto algae. Actin may even help guide other proteins — enzymes — that can cut into algal cell walls. Results from studies by Hess and his colleagues suggest that these seemingly simple amoebas may be far more advanced than they first seemed.
One might even consider them one-celled engineers. Debra Brock is a biologist at Washington University in St. Louis, Mo. Many simply refer to them as Dicty. These soil-dwelling organisms dine on bacteria. Dicty usually live solo. But when food is scarce, tens of thousands may merge, clumping into a dome. Amoebas eat algae, bacteria, plant cells, and microscopic protozoa and metazoa — some amoebas are parasites.
They eat by surrounding tiny particles of food with pseudopods, forming a bubble-like food vacuole. The food vacuole digests the food. Wastes and excess water are transported outside the cell by contractile vacuoles. An amoeba, a single-celled organism lacking internal organs, is shown approaching a much smaller paramecium, which it begins to engulf with large outflowings of its cytoplasm, called pseudopodia.
Once the paramecium is completely engulfed, a primitive digestive cavity, called a vacuole, forms around it. In the vacuole, acids break the paramecium down into chemicals that the amoeba can diffuse back into its cytoplasm for nourishment. The process of engulfing drops of liquid is known as pinocytosis, also known as cell drinking, according to Dosage Form Design Considerations.
For centuries, the various systems of classifying organisms, including amoebas, were based on similarities in observable characteristics and morphology. Historically, amoebas were classified together in a single taxonomic group called Sarcodina, distinguished by their use of pseudopodia. Sarcodina amoebas were subdivided based on the type of pseudopodia, according to a article published in the journal Protistology.
However, this system of classification was not illustrative of the evolutionary relationships between the various amoebas. It was not a family tree so to speak. Molecular phylogenetics changed the course of taxonomic classification for eukaryotes especially. Based on the analyses of SSU rDNA and other DNA sequences, eukaryotic organisms are now organized in a manner that better represents their evolutionary relationships — the phylogenetic tree, according to the Protistology article.
Each lineage in a phylogenetic tree is depicted by a branched structure. In this system, the first levels are known as "supergroups. Animals and fungi are in the group Ophiskontha. Amoeboid protists and some parasitic lineages that lack mitochondria are part of Amoebozoa. Heterotrophic protists — organisms that take in nutrients from other organisms — are part of Excavata, while plants and most other photosynthetic organisms are part of Archaeplastida, according to the Encyclopedia of Evolutionary Biology.
In addition, he noted that amoebas are also present within Rhizaria, Excavata, Opisthokonta for example, Nucleariids, which have filopodia and within the Stramenopiles for example, Labyrinthulids. Amoebas are known to cause a range of human diseases. Amebiasis, or amoebic dysentery, is an infection caused by Entamoeba histolytica, a human intestinal parasite, according to the Centers for Disease Control and Prevention CDC.
According to the National Institutes of Health NIH , Entamoeba histolytica can invade the colon wall and cause colitis, or can cause severe diarrhea and dysentery. Though the disease can occur anywhere in the world, it is most common in tropical regions that have substandard sanitation and crowded conditions. If you have a camera or cell phone mounted on your microscope, the slow-moving Amoebas are great models to practice your microphotography and video-making skills.
Another feature that you can easily observe is the abundance of crystal-liked inclusions inside Amoeba proteus. Most crystals of Amoeba proteus are in a bi-pyramidal shape. These crystals are contained in vacuoles and composed of triuret, a nitrogen waste product. Other species of Amoebas have their crystals in different shapes, like spheres, sheets, and even croissant-shaped crystals. Here are some examples of crystals in different species of Amoebas.
Some large Amoebas also have glycogen bodies to store their nutrient reserve. These glycogen bodies are glossy spheroids and vary in size. Glycogen is a form of sugar and in our body, we store glycogen in the liver and muscle. When the amoeba digests large amounts of diatoms, you can even see the oil droplets inside the cell of amoeba.
This is because some diatoms are tiny oil producers! Some large amoebas contain bacteria and small green algae inside their cytoplasm. For example, green algae live inside can provide additional energy to their host the amoeba , making the amoeba can live in nutrient-poor environments.
The answer is no. The family of Amoebas comprises very diverse members with over 15, described species. Although they all share one characteristic — moving by pseudopods, they can be totally different in shapes and sizes.
B Thecamoeba. The body of Thecamoeba often forms a wrinkled cornucopia shape. C Vampyrella got its name by the way it feeds. Vampyrella sticks to its victims usually algae , makes a large hole in the algal cell wall and sucks the protoplast of the algae. Credit: Pelomyxa and Thecamoeba — eol. Amoebas can be divided into two major groups: naked amoeboids subclass: Gymnamoebae and shelled amoeboids subclass: Testacea.
These Amoebas with soft, gel-like cell bodies, like Amoeba proteus, Pelomyxa, Thecamoeba, and Vampyrella , are all naked amoeboids. Some shelled Amoebas make the tests entirely by themselves and the materials could be organics, siliceous containing silica or calcareous containing calcium carbonate components produced by the Amoebas. These tests are called autogenic tests. Some shelled Amoebas prepare their tests by collecting particles of sediment around them and glue these mineral particles together by slime ingredients secreted from the cells.
These tests are called xenogenic tests. Credit: Frank Fox on wiki. These shelled amoebas can be collected with the same methods as naked amoebas. However, since the tests could easily break, you have to be careful when examining them under the microscope.
The weight of coverslip may crash the tests of shelled amoebas. Use the microscopic slides with a single concave or add some dots of Vaseline under the corners of the coverslip to provide more space for these creatures.
The Greek meaning describes this microbe as the Sea God Proteus that has a constantly changing shape. Amoebas belong to the Kingdom of the protists a protist is any eukaryotic organism that is not an animal, plant, or fungus. However, in terms of classification, the position of amoebas just like their shape — consistently changing. In the early days, when the microscopy was the only way to characterize the microorganisms, amoebas were classified as Phylum Sarcodina with several other species like Heliozoa.
Once the molecular phylogenetics classify a species by its genetic materials was introduced, amoebas are now in Phylum Amoebozoa. We have however to keep in mind that the classification of the protists is presently much debated. Heliozoa is commonly known as sun-animalcules.
Unfortunately, it is true. Although most amoebas are harmless to human beings, some rare species can be parasitic inside the human body.
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