Amoeba proteus

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This very large polypodial amoeba usually lives in very clear and well-oxygenated water. It feeds on other protozoans, algae, rotifers and even other smaller amoeba. The protozoan is continually throwing out pseudopodia in all directions with one pseudopodium becoming dominant for a short while. When the amoeba has two or three pseudopodia probing around the tips of those that are to be retracted become a gel forcing the cytoplasm back into the main cell body and pushed into the new leading pseudopodium. New pseudopodia are being continually formed and retracted always testing the environment for a likely meal or possible danger. Sometimes while making observations of this very well designed predator I have seen certain ciliates come to a full stop when coming into contact with the cell membrane of the amoeba, it is as though they have been hit with a stun gun. The amoeba quickly seizes the opportunity and flows over the prey and forms a vacuole around the animal. Measurements done with the Ph of the food vacuoles of amoebas have shown that to start off with the contents are acidic. It is only after enzymes have been emptied into the vacuole, turning the watery solution alkaline that digestion and assimilation can proceed. I have made observations and also filmed other amoebas being consumed by the much larger Amoeba proteus, which is very strange seeing an amoeba inside another amoeba. Keeping these amoeba's can be difficult but I have managed to keep a natural culture going for nearly three weeks with just the help of standing rain water, which I use to top up the water lost by evaporation.

The arrows in the photograph point to three common cell inclusions that are almost always in evidence when this microbe is viewed under the microscope. (a) This is the water expelling vacuole and usually starts at the posterior (uroid) end of the microbe. It gradually enlarges and moves down along the cell body along with the cytoplasm. This vacuole will move around the cell for a while until it reaches a certain size where it is then passed up through the cytoplasm to the membrane and emptied into the surrounding medium through a small pore. When the water is expelled from the vacuole it does not always completely empty but may start to refill immediately; at other times it completely vanishes without a trace. This process is repeated over again and occurs at regular periods. Sometimes two or three WEV may be growing at the same time; this probably depends on the chemicals in the water and also the health of the organism. The next organelle is the food vacuole (b) and depending on the species of amoeba may be very numerous. Amoebas capture their prey by surrounding it with their pseudopodia and engulfing it into a vacuole full of water. Enzymes are then gradually emptied into this watery vacuole and the prey is slowly digested and converted into energy for the amoeba. Sometimes if you are lucky you can actually see the living prey still struggling while trapped inside the vacuole. The nucleus (c) is a very important organelle in the cell body and can be seen even in an ordinary light microscope without any optical enhancement. The nucleus is a membrane bound organelle and carries the genetic information which the cell needs to grow, reproduce etc. The nucleus is carried around the cell body of the amoeba tumbling along with the rest of the cell inclusions in the fluid cytoplasm.

Photograph (a), was taken on a Leitz Orthoplan microscope with a X16 planapo brightfield objective and with a darkfield condenser in place. The amoeba had thousands of small square shaped granules within its cell body. The crystals make it very easy to observe the outer plasmagel state because while the inner plasmosol is moving the plamagel remains stationary. It must be remembered that what we see when we peer down the microscope is a two dimensional image of a three dimensional animal. In reality various parts of the amoeba are touching a surface and some parts are free of any surface, so the protist tends to creep along by dropping a pseudopodium here and there and pulling its self along by gripping the substratum. Most of the amoeba proteus that I have observed appears to be covered with these granules and they show up very well in this type of contrast enhancement. The crystals can be observed in bright field, all you need to do is close down the condenser iris slightly more than normal and there they are. Figure (b) was taken on a Zeiss photomic 111 and shows the many square granules much clearer. I have been unable to find out what these crystals consist of and why the amoeba produces them in the first place. These images have been altered with the aid of Photoshop which can be used to crop unwanted detail or sharpen the image up a little bit.

This photograph was taken with a X25 Leitz differential interference objective and shows the food vacuole, nucleus and two water expelling vacuoles. Differential interference is very costly and can only become available through universities where it is sometimes employed for observations on cell bodies and inclusions. The images look very attractive but it is not really necessary to own this equipment to do worthwhile science.

Photograph (c) was taken with a Leitz X16 planapo phase contrast objective and shows the many algae cells that have been ingested by the amoeba. It is very interesting to watch these animals feed and how slowly they throw a section of their pseudopodium over and around their prey and then just carry on moving with the prey safely encased in a food vacuole. Sometimes if you are lucky you can see the amoeba get rid of its waste by just opening a pore on the surface of the cell membrane and ejecting the waste into the surrounding water. Phase contrast is expensive and can be difficult to set up for the first time user, but once mastered it becomes apparent to the observer how useful this tool becomes when observing protozoa. Many parts of the amoeba would be very difficult to observe with bright field and detail would be lost.

This photograph shows the granular nature of the nucleus of this species of amoeba.This was taken with a X40 Nomarski objective, using 160 Tungsten slide film. Many food vacuoles can also be seen in various stages of development.

This shows the food vacuole in action. The vacuole is full of enzymes which will eventually digest the prey. It is easy to watch this happening down the microscope even with the smallest of species. Not all amoebas throw out numerous pseudopodia and some do not have any at all.

This photograph is of the tail end of an amoeba and is called the Uroid. Not all amoebas have this feature and it can be used for identification purposes for those that have. X40 phase contrast.

This photograph was taken with a differential interference objective and shows a large contractile vacuole of an Amoeba proteus. There are food vacuoles visible in various stages of digestion also.

This photograph was captured from a video that I have done on the amoeba proteus. It shows a large nucleus along side a contractile vacuole. Also note the many captured algae cells within the cytoplasm.

This phase contrast image shows the contractile vacuole just after it had emptied its contents into the surrounding water. The rectangular shaped objects are triuret crystals while the very dark circular objects are all most certainly mitochondria. The mitochondria's main function is aerobic respiration.