Amoebas (or amoebae) are among the simplest living things on the planet. These microscopic, single-celled organisms are fascinating creatures; they can be mostly found in lakes and ponds, and some are parasitic towards plants, humans, and other animals. But amoebas themselves are not classed as animals – they are part of the protozoa kingdom.

The simplicity of an amoeba can be deceptive. These unicellular organisms come in different shapes and forms, and are capable of a primitive kind of locomotion.

But what on earth do amoebas eat? What can be small enough to fit into an amoeba’s mouth? Do amoebas even have mouths? Perhaps you have heard that amoebas eat human brains? We’ll be answering all these questions and more!

The short answer is that the majority of amoebas eat bacteria while some species eat other protozoa and algae. It is the parasitic amoeba that feed on plant material, animal tissue, and brains (including human brains!). Join us to find out all about amoeba diets and the way in which they consume their food!

Brief Amoeba Biology

In order to understand what an amoeba eats, we need to understand how they eat. Let’s take a closer look at their biology…

What Is An Amoeba?

Amoebas are simple, eukaryotic (unicellular or multicellular) organisms. They are part of the protozoa kingdom along with a whole host of strange and intriguing single-celled organisms.

Their bodies are made up of a flexible cell membrane – allowing them to change their shape and effectively “flow” along – and cytoplasm contained inside. Within the cytoplasm there are several cell bodies including:

  • A nucleus (or nuclei – some species have hundreds!) which contains their DNA, controlling both growth and reproduction processes
  • Organelles – these specialized cell bodies are responsible for a wide range of functions such as the production of energy and the transport of proteins. One well-known example is the mitochondria. Most amoeba organelles are also found in all eukaryotic cells (including yours and mine!)

Some parasitic amoebas lack certain organelles such as Entamoeba histolytica (these can be parasitic towards humans and cause dysentery) do not have an organelle which modifies and transports proteins called the golgi apparatus.

Other amoeba species have extra organelles like one free-living amoeba called Mastigamoeba balamuthi which lacks mitochondria but possesses organelles called hydrogenosomes. These amoebas live in anaerobic environments (without oxygen) and do not need other organisms to survive.

Reproduction

To reproduce, amoebas will effectively split into two with the cell and organelles dividing themselves between the two new cells.

Movement

The flexible membrane of an amoeba lets them change shape, extending and retracting cytoplasms into parts called pseudopodia (“false feet”). Some amoeba species use the pseudopodia to wrap around a food item, totally engulfing it and then digesting it.

The type of pseudopodia an amoeba possesses depends on the species, but there are 4 main kinds which dictate their method of movement.

It is theorised that amoebas have a type of chemical detection system to locate their prey because they do not have to touch a prey item to know it is there.

Digestion

This is where it gets really cool. To digest food, amoebas surround a food item with their cytoplasm which becomes more fluid to help this process. They can digest both solid and liquid foods using methods called phagocytosis and pinocytosis which can be likened to eating and drinking!

Some amoebas attach to their food through receptors on the surface of their cell membrane. Others surround the food item and draw it into the cell interior in a separate “sack” called a vacuole. This prevents the food from escaping.

The amoebas then digest the food using enzymes and absorb the nutrients. The waste is cast out through the cell membrane.

The chemical detection system allows an amoeba to adapt its food catching technique depending on the type of prey it is hunting. For example, fast prey items like paramecium (another kind of single-celled protist) which moves quickly, or can be consumed slowly such as algae which is stationary. Pretty smart! So what do amoebas eat?

What Do Amoebas Eat?

The diet of an amoeba depends on the habitat it is living in, and the species. Some amoebas exist without needing other organisms for their survival. Others feed only on plant matter, bacteria, or fungal cells. Some may feast on animal matter. And others still are parasites. Many are not fussy and will eat any organic matter (such as decaying vegetation) available to them, as long as it is smaller than them!. We’ll take a look at a few common examples and uncover their nutritional tendencies…

Bacteria

Most known amoebas consume bacteria by phagocytosis. A well-known example of this kind of amoeba is slime-mould. Watch a video of slime-mould eating bacteria here! Amazingly, some species of amoeba carry bacteria around inside themselves just like we do. This can be a symbiotic relationship whereby the bacteria help the amoeba and get protected by the amoeba in return.

The amoeba species Cryptodifflugia operculate specialises in eating nematodes. Incredibly, this species will form a “pack” and hunt for the nematodes just as wolves pack-hunt for they prey!

Algae

Many amoebas eat algae. Species such as Vampyrella lateritia consume the entire contents of algal cells. Some do this by cutting a hole in the algal cell and “sucking out” the contents, while others burrow into the cell and eat it from the inside out! One example is the species Viridiraptor invadens.

Watch an amoeba eat an algal cell here!

Fungi

Some species of amoebas eat fungal cells. One example is the group called the vampyrellids. These creatures drill round holes in the cell wall of the fungi. Then, they produce these enzymes once they have attached themselves to the fungal cell. The enzymes break through the cell wall and the amoeba is able to “suck” the contents out.

One species, Gaeumannomyces graminis, has diet preferences that are useful for people. Their main prey is the fungal cells of a wheat root pathogen which causes serious disease in wheat crops.

Decaying Organic Matter

Amoeba proteus is one of the most well-known amoeba species because it is often used in classrooms and labwork to demonstrate the functioning of an amoeba. It has a diverse diet and can adapt to a range of foodstuffs, but is most commonly found eating its way through decaying organic matter on the bottom of freshwater bodies.

Plant Parasites

There’s a whole group of amoebas called Plasmodiophorida (Phytomyxea) which specialise in parasitising plants. They are adapted to higher plants such as the amoeba species Sorosphaera viticola which is a parasite on grapevines. Other species attack marine plants such as brown algae.

Phytomyxids are particularly notable for their often devastating effect on arable crops. They can carry viruses which they transfer to host plants, or play the role of pathogens on host plants themselves. An example of this is Plasmodiophora brassicae which causes clubroot disease in brassicas like broccoli and kale.

Animal Parasites

There are several species of amoebas which can be found in vertebrates. Certain species such as Entamoeba invadens is a parasite on reptiles specifically and cannot be transmitted to other animals.

Entamoeba histolytica is prevalent in tropical and subtropical regions and causes amebiasis particularly in humans and primates, but also in domestic animals and sometimes other mammal species. The disease they cause is commonly called dysentery, and is transmitted into the gut via food or water that has been contaminated with feces that contains infected material. The amoebas then eat the intestinal cells. This disease can cause severe illness or on some occasions death, but is not as prevalent as viruses or bacteria in terms of causing illness in people.

Human Parasites

Now we get to the famous and terrifying story of the brain-eating amoebas! But please note that this disease is very rare and the number of incidents per year is very low. The amoeba species Naegleria fowleri can be transmitted into the human brain via the nose in lakes or rivers. Once it reaches the brain it will consume brain cells, causing encephalitis. Usually this is fatal to the host.

You can find out more here!

Some species of the genera Acanthamoeba and B mandrillaris may cause serious infections in human lungs and skin. The genus Acanthamoeba can enter the human body usually through soft contact lenses which have not been properly sterilised.

The amoebas that are parasitic towards humans can be found in soil, and both fresh and saltwater bodies in many regions of the world, but mostly tropical and subtropical areas.

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