Category Archives: protists

Friday Fellow: Common giardia

by Piter Kehoma Boll

Parasites are always a group eager to be featured here, and human parasites have a special place in our hearts… sometimes literally. Today’s species, however, has a special place in our small intestine.

Called Giardia lamblia, sometimes also identified under the outdated synonyms Giardia duodenalis or Giardia intestinalis, our species has not a common name, but as it is the most popular and widespread species of the genus Giardia, I decided to call it simply the common giardia.

The common giardia is a flagellated unicellular organism that affects not only humans but several other mammal species. In the wild, the common giardia exists in the form of an inert cyst that can survive for prolonged periods and under different environmental conditions.

giardia_cyst_wtmt3

A cyst of Giardia lamblia. Credits to Centers for Disease Control and Prevention.

When the cysts are ingested by humans or other mammals, they develop into the active stage, called trophozoite, once they reach the small intestine. The trophozoite is a flagellated cell with two well-developed nuclei that make it look like a smiling face. In this stage, the common giardia reproduced by simple binary fission. For a long time, it was thought that sexual reproduction did not occur at all in this species, but some recent evidence indicate that recombination may occur, although it is not very clear yet how it happens.

800px-giardia_intestinalis_28259_1729

Two trophozoites of the common giardia under the microscope. Credits to Josef Reischig.*

The ventral surface of the trophozoite is concave, forming an adhesive disk that attaches the cell to the wall of the intestine, preventing it to be transported downward the intestinal tract. Although not invading the intestinal cells, the infection of Giardia lamblia usually causes diarrhea and malabsorption. When exposed to biliar secretions, the common giardia may develop into a cyst and is thus eliminated with the feces, allowing the cycle to begin again.

Humans are very often contaminated by several means, such as by ingesting contaminated water, which may include both urban untreated water or clear water in the wild where other mammals may have defecated. It is, therefore, a common infection among hikers, people living under poor sanitary conditions and so on.

The common giardia has some peculiarities, such as the lack of mitochondria, which for some time led to the assumptions that they may belong to a very primitive group of Eukaryotes. Recently, however, a vestigial organelle that likely derived from mitochondria, named mitosome, has been found in this species, suggesting that this feature is a secondary loss caused by its parasitic life in an anoxic environment.

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References:

Adam, R. D. (2001) Biology of Giardia lambliaClinical Microbiology Reviews 14(3): 447–475.

Wikipedia. Giardia lamblia. Available at < https://en.wikipedia.org/wiki/Giardia_lamblia >. Access on 28 June 2018.

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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.

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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 stateEntomological 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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Friday Fellow: Handsome Asterisk-Diatom

by Piter Kehoma Boll

It’s time for the next diatom to be featured here. Differently from the previous ones, today’s diatom is a freshwater species commonly found in lakes of North America and Eurasia. It has also been reported for South America and Africa, but it is likely that these individuals actually belong to another, closely related species.

asterionella_formosa

Asterionella formosa from a lake of the Rocky Mountain National Park, United States

Named Asterionella formosa, this diatom has small rod-shaped cells that are 60 to 85 µm long and only 2 to 4 µm wide. The individuals usually organize themselves in colonies linked by one of the ends in a star fashion. Most colonies include eight organisms and look somewhat like an asterisk, hence I chose to give the common name asterisk-diatom to the genus, this species then being called the “handsome asterisk-diatom”, from the translation of the specific epithet formosa. However, some colonies may have up to 20 individuals and organize in a more spiral fashion.

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A spiral-shaped colony from a small lake in Spain. Credits to Proyecto Agua.*

Originally found and described from water supplies used in London, the handsome asterisk-diatom has a preference for cold waters, occurring commonly in temperate lakes under temperatures between 0 and 15 °C. During summer, when temperatures get too high and the light intensity also increases, its photosynthesis is inhibited by these two factors as well as by the increase in oxygen caused by the metabolism of the species itself as well of other algae from the phytoplanktonic community.

Sexual reproduction is not well known in the handsome asterisk-diatom, but must certainly occur, as asexual reproduction alone leads to a continuous decrease in cell size in all diatoms. Studies on genetic diversity show that this species is very genetically diverse, which proves that sexual reproduction indeed occurs and in a apparently high rate, contributing for the dominance of this species in many of the ecosystems of which it takes part.

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References:

AlgaeBase. Asterionella formosa Hassall. Available at < http://www.algaebase.org/search/species/detail/?species_id=31441 >. Access on May 25, 2018.

Belay, A.; Fogg, G. E. (1978) Photoinhibition of photosynthesis in Asterionella formosa (Bacillariophyceae). Journal of Phycology14(3): 341–347. https://doi.org/10.1111/j.1529-8817.1978.tb00310.x

De Bruin, A.; Ibelings, B. W.; Rijkeboer, M.; Brehm, M.; Van Donk, E. (2004) Genetic variation in Asterionella formosa (Bacillariophyceae): is it linked to frequent epidemics of host-specific parasitic fungi? Journal of Phycology40(5): 823–830. https://doi.org/10.1111/j.1529-8817.2004.04006.x

EOL – Enclyclopedia of Life. Asterionella formosa. Available at < http://eol.org/pages/917771/details >. Access on May 25, 2018.

Lund, J. W. G. (1950) Studies on Asterionella formosa Hass: II. Nutrient depletion and the spring maximum. Journal of Ecology38(1): 15–35.

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Friday Fellow: Pink Miniacina

by Piter Kehoma Boll

It’s time  for the next foraminifer, which is always a problematic time, but I managed to find a suitable fellow for this Friday. Called Miniacina miniacea in the scientific community, it obviously lacks a common name, so I decided to call it the pink miniacina.

Differently from the previously introduced foraminifers, the pink miniacina is a sessile and colonial species. It usually grows attached to other lifeforms, especially algae and corals. Due to its colonial nature, added to the already bigger-than-average size of foramnifers when compared to other unicellular organisms, the pink miniacina is easily visible to the naked eye and can be seen as a series of small branched organisms with an intense pink color. It is particulary common in the Mediterranean Sea, although it can be found in other places as well.

miniacina_miniacea_30-09-06_dscf3288

Several pink colonies of Miniacina miniacea growing in the Mediterranean Sea. Photo by Stefano Guerrieri.

Due to its habit of living on the surface of other sessile organisms, the pink miniacina competes with many other organisms that have the same behavior. As a result, its abundance tends to increase in deeper water, where many of such organisms find the conditions too unsuitable to live. In a few areas, the abundance of the pink miniacina may be high enough to create a “pink sand” from the shells of dead specimens.

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References:

Di Camillo, C.; Bo, M.; Lavorato, A.; Morigi, C.; Reinach, M. S.; Puce, S.; Bavestrello, G. (2008) Foraminifers epibiontic on Eudendrium (Cnidaria: Hydrozoa) from the Mediterranean Sea. Journal of the Marine Biological Association of the United Kingdom88(3): 485–489. https://doi.org/10.1017/S0025315408001045

Milliman, J. D.(1976) Miniacina miniacea: modern foraminiferal sands on the Outer Moroccan shelf. Sedimentology23: 415–419. https://doi.org/10.1111/j.1365-3091.1976.tb00059.x

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Friday Fellow: Sea Sparkle

by Piter Kehoma Boll

If you live near the sea or visit it often, you may sometimes have seen the waves glowing while breaking on the shore at night. This beautiful phenomenon is caused by the presence of bioluminescent microorganisms, the most famous of which is our newest Friday Fellow. Scientifically known as Noctiluca scintillans, it is populary known as the sea sparkle.

Bioluminescent_sea

Waves glowing blue at Atami, Japan. Photo by Kanon Serizawa.*

The sea sparkle is a dinoflagellate and is common worlwide. It is an heterotrophic flagellate and feeds on many other small organisms, such as bacteria, diatoms, other dinoflagellates and even eggs of copepods and fish. Having only a small tentacle and a rudimentar flagellum, the sea sparkle is unable to swim, making it a very unusual predator. Studies have suggested that it preys by bumping into the prey during water flow or by ascending or descending in the water column due to density differences. It can also produce a string of mucus attached to the tentacle that entagles prey and brings them to their horrible end.

noctiluca_scintillans_unica

A single Noctiluca scintillans. Photo by Maria Antónia Sampayo, Instituto de Oceanografia, Faculdade Ciências da Universidade de Lisboa.**

In temperate waters, the sea sparkle is an exclusive predator, but in tropical water it may maintain some of the ingested algae alive and use them in a symbiotic association to receive nutrients from photosynthesis. Diatoms of the genus Thalassiosira appear to be one of its favorites.

The most striking feature of the sea sparkle, however, is its bioluminescence, from which it receives its names. The light that it emits is produced by a chemical reaction between a compound called luciferin and an enzyme, called luciferase, that oxidizes it, causing it to emit light. The phenomenon is clearly visible on the sea during blooms of the dinoflagellate, which usually happen right after a bloom of its food.

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References:

Kiørbe, T.; Titelman, J. (1998) Feeding, prey selection and prey encounter mechanisms in the heterotrophic dinoflagellate Noctiluca scintillansJournal of Plankton Research 20(8): 1615–1636.

Quevedo, M.; Gonzalez-Quiros, R.; Anadon, R. (1999) Evidence of heavy predation by Noctiluca scintillans on Acartia clausi (Copepoda) eggs of the central Cantabrian coast (NW Spain). Oceanologica Acta 22(1): 127–131.

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Friday Fellow: Lyre ship diatom

by Piter Kehoma Boll

It’s time for the next diatom, and just as with the radiolarian from the last week, it’s a hard task to find good pictures and good information of any species to present here.

Today I’m introducing a species of the most diverse (I guess, or at least one of the most diverse) genus of diatoms, Navicula, a name that means “little ship” in Latin due to the shape of the cells. There are more than 1200 species in this genus, and one of them is called Navicula lyra, which I decided to call the lyre ship diatom. I have also seen it with the name Lyrella lyra, being the type-species of a genus Lyrella (little lyre) that was split from Navicula. I don’t know which one is the official form today, but it seems that Lyrella is sometimes something like a subgenus of Navicula, although sometimes both genera are not even in the same family!

Navicula_lyra

Navicula lyra, a lyre little ship. Photo by Patrice Duros.*

Anyway, the lyre ship diatom is a planktonic species that is found in all the oceans of the world, being present in species lists everywhere. It measures about 100 µm or less, a typical size for a diatom.

As with other diatoms in the genera Navicula and Lyrella, the lyre ship diatom has different varieties, which may eventually be revealed to be separate species, I guess. See, for example, the variety constricta shown below. It looks considerably different from the picture above, which appears to be from the type variety.

Navicula_lyra

Lyrella lyra var. constricta. Extracted from Siqueiros-Beltrones et al. (2017)

Despite being a widespread species, little seems to be known about the natural history of the lyre ship diatom. Aren’t you interested in studying the ecology of these tiny little glass ships?

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References:

Nevrova, E.; Witkowski, A.; Kulikovskiy, M.; Lange-Bertalot, H.; Kociolek, J. P. (2013) A revision of the diatom genus Lyrella Karayeva (Bacillariophyta: Lyrellaceae) from the Black Sea, with descriptions of five new species. Phytotaxa 83(1): 1–38.

Siqueiros-Beltrones, D. A.; Argumedo-Hernández, U.; López-Fuerte, F. O. (2017) New records and combinations of Lyrella (Bacillariophyceae: Lyrellales) from a protected coastal lagoon of the northwestern Mexican Pacific. Revista Mexicana de Biodiversidad 88(1): 1–20.

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Friday Fellow: Twisted-Spined Sponge Radiolarian

by Piter Kehoma Boll

Oh, it’s time for our next radiolarian. As as usual, it’s hard to find good information on any species. (If you work with radiolarians and have good available resources and nice species to suggest, please contact us!)

It’s hard to find pictures of live radiolarians, especially those identified to the species level, but one that I found is seen below and is called Spongosphaera streptacantha, or the twisted-spined sponge radiolarian, as I decided to call it.

4xspongospaerastreptacantha2014oct27

A nice photo of a liveSpongosphaera streptacantha. Extracted from Galerie de l’Observatoire Océanologique de Villefranche-sur-Mer.

The twisted-spined sponge radiolarian is found in warm waters in the Atlantic and Pacific oceans (perhaps the Indian too?) and, as one can notice, may have a diameter of more than 1 mm if we count the longest spines. As with most radiolarians, the cell of this species has two concentric shells and a set of spines, which are 6 to 15 in number.

The food of the twisted-spined sponge radiolarian consists of smaller organisms, such as bacteria and algae, which it captures with the long rod-like pseudopods called actinopodia.

As with most radiolarians, the twisted-spined sponge radiolarian is understudied regarding its ecology. Let’s hope more people get interested in studying this fascinating group of organisms.

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References:

Kurihara, T.; Matsuoka, A. (2004) Shell structure and morphological variation in Spongosphaera streptacantha Haeckel (Spumellaria, Radiolaria). Science Reports of Niigata University (Geology), 19: 35–48. http://hdl.handle.net/10191/2141

Matsuoka, A. (2007) Living radiolarian feeding mechanisms: new light on past marine ecosystems. Swiss Journal of Geosciences, 100: 273-279. https://dx.doi.org/10.1007/s00015-007-1228-y

Radiolaria.org: Spongosphaera streptacantha. Available at: < http://www.radiolaria.org/species.htm?sp_id=90 >. Access on August 8, 2017.

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