Friday Fellow: Common Pelomyxa

by Piter Kehoma Boll

It’s time to dig deep into the mud again and bring up a peculiar protist, the third species of the clade Amoebozoa to be featured here. Its binomial name is Pelomyxa palustris, and I decided to call it the common pelomyxa.

Measuring up to 5 mm in length, although usually having less than 1 mm, the common pelomyxa is considered a “giant amoeba”. In fact, the Giant Amoeba Chaos carolinense, previously featured here, was once classified in the genus Pelomyxa, but currently we know that they are not closely related at all. While the true giant amoebas of the genus Chaos are closely related to the common amoebas of the genus Amoeba, the species in Pelomyxa belong to a completely different group of amoebas.

A specimen of the common pelomyxa. The large pseudopod is to the right and the small uroid can be seen projecting from the cell at the upper left. Credits to Proyecto Agua.*

The cell of the common pelomyxa has a somewhat cylindrical shape with a single, large, semicircular pseudopod at the front, thus moving basically always in the same direction, forward, differently from the more classical amoebas with several pseudopods and the ability to move in any direction. At the opposite side of the cell, the common pelomyxa has a small, also semicircular appendix called the uroid that is covered by several small non-motile flagella. The flagella are surrounded by small cytoplasmic projections (villi) that are easily seen under the microscope.

The common pelomyxa lives buried in the sediments of freshwater lakes throughout the northern hemisphere, especially those rich in decaying organic matter. It slides through the mud while feeding on smaller microorganisms and organic debris. Such an environment is characterized by the complete absence or extremely low concentrations of oxygen. As a result, the common pelomyxa is anaerobic and even lacks mitochondria. For this reason, it was once considered part of a very primitive group of eukaryotes that diverged before the incorporation of the endosymbiotic bacteria that would evolve into mitochondria. Currently, however, it is known that their lack of mitochondria is actually due to a secondary loss and they seem to be related to true amoebas and slime molds.

More than only lacking mitochondria, the cell of the common pelomyxa has a lot of peculiar features. Depending on the size of the cell, it may contain a few to several hundred nuclei. The cytoplasm also appears to lack several typical eukaryotic organelles, such as the Golgi apparatus and the endoplasmic reticulum. There are, however, many, many small vacuoles, so many that the cell usually has a foamy appearance.

Endosymbiotic bacteria are also found in great numbers in the cytoplasm of the common pelomyxa. After several years of research, it seems that these bacteria are obligate symbionts. Perhaps they help this strange amoeba to perform some of the tasks that should be done by the several organelles that it lacks.

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References:

Goodkov, A. V.; Chistyakova, L. V.; Seravin, L. N.; Frolov, A. O. (2004) The concept of pelobionts (Class Peloflagellatea): Brief history and current state. Entomological Review 84(Suppl. 2): S10–S20.

Wikipedia. Pelomyxa. Available at < https://en.wikipedia.org/wiki/Pelomyxa >. Access on May 26, 2018.

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic License.

Friday Fellow: Giant Amoeba

by Piter Kehoma Boll

The adjective “giant” can be quite relative. When regarding microorganisms, even something with a few milimeters can be considered a giant, and that is the case with the giant amoeba Chaos carolinense (sometimes wrongly written as Chaos carolinensis).

A chaotic mess as any good amoeba. Photo by Tsukii Yuuji.

Measuring up to 5 mm in length, the giant amoeba is a freshwater organism and is easily seen with the naked eye and, since it is also easily cultivated in the laboratory, it became widely used in laboratory studies.

As with amoebas in general, the giant amoeba has an irregular cell with several pseudopods that can contract and expand. The cell has hundreds of nuclei, as it is common with species of the genus Chaos, this being the main difference between them and the closely related genus Amoeba.

The diet of the giant amoeba is variable and includes bacteria, algae, protozoan and even some small animals. In the lab, they are usually fed with ciliates of the genus Paramecium.

A specimen of Chaos carolinense feeding on several individuals of Paramecium. Photo by Carolina Biological Supply Company.*

Wouldn’t the giant amoeba make a nice unicelular pet?

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References:

Tan, O. L. L.; Almsherqi, Z. A. M.; Deng, Y. (2005) A simple mass culture of the amoeba Chaos carolinense: revisit. Protistology, 4(2): 185–190.

Wikipedia. Chaos (genus). Available at: <https://en.wikipedia.org/wiki/Chaos_(genus)&gt;. Access on June 20, 2017.

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This work is licensed under a Creative Commons Attribution-NonCommerical-NoDerivs 2.0 Generic License.

Friday Fellow: Many-Headed Slime

by Piter Kehoma Boll

What would you think if I told you that a slime can think and even solve small puzzles? You would probably take it as an April fool’s joke, but it’s true!

Our newest fellow comes from an yet unexplored kingdom in our Fridays, the kingdom Amoebozoa. Its name is Physarum polycephalum, sometimes called the many-headed slime. It is a slime mold that lives in decaying leaves and logs in forests all over the world.

If you enter a forest during a rainy season, you may be able to find some of them growing on decaying matter. They look like network of slimy yellow veins and move very slowly, looking for food, which consists of microorganisms such as bacteria or even fungal spores.

This is what the many-headed slime looks like as a plasmodium. Credits to flickr user “frankenstoen”.

This network phase is called plasmodium, the slime mold’s vegetative stage, during which it is active and grows, moving around in search for food. The plasmodium consists of a large syncytium, i.e., a group of cells fused together becoming something like a big cell with several nuclei.

If the environment gets too dry, the plasmodium will dissecate and become a sclerotium, a hardened dormant phase. If the food supply runs out, it will develop into the reproductive stage, where it stops to move and produces spores, which will be released in the environment. Once the conditions are favorable, the spores will germinate and release several cells that fuse to become a new plasmodium.

The many-headed slime is very easy to be maintained in a lab, so it has become a model organism. Several recent studies have shown that it is a formidable creature. It exhibits some behavioral responses indicating an intelligence similar to that of eusocial insects. It seems to have some sort of external memory, enabling it to avoid previously visited sites, and is even able to solve some basic puzzles, such as the shortest path problem, and anticipate periodic events. Also, it may be able to detect and differentiate colors.

There are even attemps to find a way to use it as a substrate to make bio-computers! The many-headed slime is certainly an amazing fellow!

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References and Further Reading:

Adamatzky, A. 2013. Towards slime mould colour sensor: Recognition of colours by Physarum polycephalum. Organic Electronics, 14(12): 3355-3361. DOI: 10.1016/j.orgel.2013.10.004

Becchetti, L.; Bonifaci, V.; Dirnberger, M.; Karrenbauer, A.; Mehlkorn, K. 2013. Physarum can compute shortest paths: convergence proofs and complexity bounds. Automata, Languages and Programming, 7996: 472-483

Caleffi, M.; Akyldiz, I. F.; Paura, L. 2015. On the solution of the Steiner Tree NP-Hard problem via Physarum BioNetwork. IEEE/ACM Transactions on Networking 23(4): 1092-1106. DOI: 10.1109/TNET.2014.2317911

Nakagaki, T.; Yamada, H.; Tóth, A. 2000. Intelligence: Maze-solving by an ameboid organism. Nature, 407: 470. DOI: 10.1038/35035159

Saigusa, T.; Tero, A.; Nakagaki, T.; Kuramoto, Y. 2008. Amoebae anticipate periodic events. Physical Review Letters, 100: 018101. DOI: 10.1103/PhysRevLett.100.018101

Wikipedia. Physarum polycephalum. Available at: < https://en.wikipedia.org/wiki/Physarum_polycephalum >. Access on March 30, 2016.