Amoebas live in nearly all environments of Earth. Unique adaptations and survival strategies of these canny microorganisms make them integral to ecosystems. Unseen, these single-celled microbes are vital to environmental balance, being both predators and prey.
Amoeba clockwise from top right: 1. Amoeba proteus 2. Actinophrys sol 3. Acanthamoeba sp. 4. Nuclearia thermophila 5. Euglypha acanthophora 6. neutrophil ingesting bacteria. These six are detailed below. There are multiple credits for this image.
What are Amoebas?
Amoebas (also amoebae) are some of the most fascinating microorganisms on the planet. Their unique structure, adaptability, and behaviors make them a subject of endless curiosity and research.
Single-celled microorganisms, amoebae belong to kingdom Protista and phylum Amoebozoa. They're characterized by flexible shapes and ability to form temporary projections or pseudopodia, aka false feet. These are extensions of their bodily cytoplasm.
The video is here: Amoeba hunts and kills paramecia and stentor - YouTube
They extend and use the mutable appendages to move around and capture food. To travel, an amoeba sends out pseudopodia which attach to a surface, and thus pulls itself along. This adaptability gives them a fluid morphology, enabling them to live in diverse environments.
Most amoebas are solitary organisms. Certain species can behave colonially under specific conditions. This allows them to work together for survival or reproduction. For instance, some amoebae can aggregate in stressful environments, forming a temporary multicellular structure.
The Protista Kingdom covers creatures which are not fungi, plants or animals. It derives from Greek meaning "the very first". Protista include the sub-kingdom protozoans, slime molds, chrysophytes, dinoflagellates and euglenoids.
Protozoans clockwise from top left:
1. Blepharisma japonicum, a ciliate; 2. Giardia muris, a parasitic flagellate; 3. Centropyxis aculeata, a testate (shelled) amoeba; 4. Peridinium willei, a dinoflagellate; 5. Chaos carolinense, a naked amoebozoan; 6. Desmarella moniliformis, a choanoflagellate. Multiple credits exist for this pic.
Amoebae belong to the protozoans. Most amoebae are harmless or beneficial, but there are a few rogues.
Amoebae Causing Sickness & Death
Like zombies, some amoebae only love you for your brains. The microbe Naegleri fowleri, aka brain-eating amoeba, cause serious central nervous system infection. The amoeba lives in warm fresh water bodies and enters a human organism through the nose.
Acanthamoeba can also cause diseases in humans. These include keratitis and granulomatous amoebic encephalitis (GAE). The latter is often but not always seen in immunosuppressed patients.
GAE is caused by when the amoebae enter the body through an open wound and then spread to the brain. The combination of host immune responses and secreted amoebal proteases causes massive brain swelling resulting in death in 95% of those infected.
Besides brains, Acanthamoeba attack the eyes. Keratitis, swelling of the cornea, is identified by inflammatory cells and congestion of the ciliary body (ie eyelashes or eyelids). It's linked to infectious and noninfectious conditions and affects the whole body or only surfaces of the eye.
Entamoeba histolytica is also a health risk. This microbe is responsible for amoebic dysentery, affecting approximately 50 million people worldwide annually.
Like many other microbes, amoebas are ubiquitous and found in various habitats, from freshwater ponds and streams to moist soil and marine ecologies. They delight in regions of rich organic matter and actively explore their environment.
Some species are found in more extreme conditions, such as hot springs, salt lakes, volcanic vents or the deep sea. Fairly young on the ecological timeline, amoebae first appear 750 million years ago; compare to 3.45 billion years for bacteria.
Feeding Habits of Amoebae
Amoebas are heterotrophic, feeding on bacteria, algae, and other small microorganisms. A heterotroph can't produce its own food and relies on nutrients from sources of organic carbon, mainly plant or animal matter.
In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Heterotrophic organisms include all animals including humans, fungi, some bacteria, protists and many parasitic plants.
Amoebae use the process of phagocytosis to ingest food. The amoeba extends pseudopodia to envelop prey or particles, forming a food vacuole. It uses lysosomes, a collection of organelles, to digest the matter.
Lysosomes, single membrane-bound organelles, are found in many animal cells. These spherical vesicles are full of hydrolytic enzymes to digest an assortment of biomolecules. The amoeba digests food within 5-30 minutes. Metabolic wastes include ammonia and water.
Amoebas are important to keeping bacterial populations in check and recycling nutrients in their habitats. They ensure smooth operation of the decomposition process in nature by consuming excess bacteria.
Reproduction of Amoebas
Amoebas reproduce asexually, by binary fission. In this process, an amoeba divides into two identical daughter cells, each with a copy of genetic material. Under optimal conditions, this causes rapid population growth with some species doubling in number every 24 hours.
Some species such as Acanthamoeba form cysts to endure unfavorable conditions such as drought, thus surviving until environmental factors improve. Dormant cysts can last for years.
The lifespan of an amoeba varies significantly among species, ranging from days to months. Environmental conditions, such as temperature, food and moisture availability, can influence their longevity.
Amoebas are typically not visible to the eye. Their size ranges from 10 to 500 micrometers. To see them clearly, at least 400x magnification with a microscope is recommended.
At this magnification, unique movements and characteristics come into view. They're always intriguing subjects for microscopists and biology enthusiasts.
Types of Amoeba
Amoeba proteus
One of the most studied amoebas, Amoeba proteus is known for its size and distinct movement patterns. It is commonly found in freshwater environments and serves as a model organism in many biological studies. It feeds primarily on smaller microorganisms.
Actinophrys sol
This unique amoeba, also known as "sun animalcule," has a star-shaped appearance due to its radiating pseudopods, which it uses to capture food. It usually inhabits environments of slow-moving fresh water, and can be seen through a microscope.
Acanthamoeba sp.
Known for detrimental effects on human health, Acanthamoeba can cause serious infections. This genus is often found in soil and water and is notorious for its resilience in harsh conditions.
Many Acanthamoeba species are present in soil and freshwater. These amoebas can cause keratitis, particularly among contact lens wearers.
Nuclearia thermophila:
A thermophilic amoeba at home in high-temperature environments, Nuclearia thermophila is a fascinating extremophile. Other extremophiles include those acid or high saline environments.
Euglypha acanthophora:
With a protective siliceous shell, this amoeba is noted for its ecological significance in freshwater habitats. It feeds on bacteria and algae. It has distinct morphological features.
This amoeba builds protective shells from silica, which gives it a distinct appearance and nickname "shelled amoeba". Found mainly in freshwater, it consumes organic debris and builds its shell from microscopic grains of sand.
Neutrophil ingesting bacteria:
Although not true amoebas, some cells have amoebic properties. A compelling example of amoebas at work is seen in neutrophils, a type of white blood cell. It exhibits amoeboid movement during the ingestion of bacteria. This similarity highlights essential processes in both immune defense and microbial ecology.
There's an excellent video clip here:
Immune Cells Eating Bacteria (Phagocytosis) - watch the cells decimate the bacteria
Facts About Amoebae
Amoebas are among the simplest forms of life on Earth.
Their ability to change shape allows them to navigate through various environments effectively.
They can exist in anaerobic conditions, meaning they can survive without oxygen.
Many species are essential in controlling bacterial populations in ecosystems.
Amoebas can change their shape for movement and feeding due to their flexible cell membranes, which sets them apart from most other cells.
Equipped with lysosomes, they assist in digesting the food they engulf, showcasing their efficient nutrient absorption mechanism.
Some amoebas can survive extreme conditions, including high temperatures—a testament to their robust nature.
Their ability to form cysts allows them to endure unfavorable environmental conditions, making them exceptionally resilient.
As crucial participants in the food web, amoebas are both prey for larger organisms and predators for nutrient recycling, maintaining ecological balance.
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