Category Archives: protists

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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Friday Fellow: Pink Cellular Slime Mold

by Piter Kehoma Boll

Protists have always been problematic organisms, and today’s Friday Fellow is not different. In fact, it has probably been one of the most problematic ones. Known scientifically as Acrasis rosea, it has no common name, as you may have guessed already, so I will call him the pink cellular slime mold, as I saw him being called once.

acrasis_rosea_31330

Isolated (or not so much) cells of Acrasis rosea. Photo by Shirley Chio.*

The pink cellular slime mold is a single-celled organism with an amoeboid shape. It feeds on a variety of bacteria and yeasts and is commonly found in decaying plant matter. When the food supply is completely consumed and the cells start to starve, they gather and form a colony that act as a single organism that moves like a plasmodium similar to that of slime molds. For this reason they were originally called cellular slime molds and considered related to other organisms showing a similar behavior, such as those of the genus Dictyostelium.

This plasmodium moves through the formation of “pseudopods”. Eventually the cells start to form a pile reaching up into the air that produce fruiting bodies in the form of branched chains of spores. There is a slight division of labor between stalk and spore, but both groups of cells are viable to produce a new generation.

799px-acrasis_rosea_31095

The chains of spores are visible in this image of the pink cellular slime mold during its plasmodium phase. Photo by Shirley Chio.*

The whole process is similar to what is seen in species of Dictyostelium, but the division of labor and the morphology of the plasmodium and the fruiting bodies are a bit more complex. However, with the advancement of molecular phylogenetics, all the slime mold and cellular slime mold classification fell apart.

While Acrasis was revealed to be an excavate, being closely related to organisms such as the euglenas and parasitic flagellates, Dictyostelium is closely related to the true slime molds, such as the already presented here many-headed slime.

But the excavates are still a problematic group among the protists, and so the real position of the pink cellular slime mold may not be settled yet.

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References:

Bonner, J. T. (2003) Evolution of development in the cellular slime molds. Evolution and Development 5(3): 305–313. http://dx.doi.org/10.1046/j.1525-142X.2003.03037.x

Olive, L. S.; Dutta, S. K.; Stoianovitch, C. (1961) Variation in the cellular slime mold Acrasis rosea*. Journal of Protozoology 8(4): 467–472. https://dx.doi.org/10.1111/j.1550-7408.1961.tb01243.x

Page, F. C. (1978) Acrasis rosea and the possible relationship between Acrasida and Schizopyrenida. Archiv für Protistenkunde 120(1–2): 169–181. https://doi.org/10.1016/S0003-9365(78)80020-7

Weitzman, I. (1962) Studies on the nutrition of Acrasis roseaMycologia 54(1): 113–115.

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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).

Chaos_carolinense

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.

Chaos (Pelomyxa) carolinensisChaos with paramecium prey

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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Friday Fellow: Bubble Globigerina

by Piter Kehoma Boll

A little more than a year ago I introduced the first foraminifer here, the tepid ammonia. Now it is time to bring the second one, this time a planctonic species that is rather famous and whose scientific name is Globigerina bulloides, or the bubble globigerina as I call it.

Globigerina_bulloides

A live specimen of Globigerina bulloides. Photo extracted from Words in mOcean.

This species can be found throughout the world, but it’s more common in cold subantarctic waters and a little less common in subarctic waters. The most common areas are the North and South Atlantic and the Indian Oceans, but the tropical records are most likely a misidentification of other closely related species.

The bubble globigerina usually lives in the upper 60 m of the water column, at least while reproducing, and feeds on other planktonic organisms, especially microscopic algae. In oder to maximize the ability of their gametes to meet in the vast extension of the ocean, the bubble globigerina synchronizes its sexual cycle with the moon cycle, reproducing during the first week after the new moon. It is, therefore, a kind of biological calendar.

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ResearchBlogging.orgReferences:

Bé, A. W. H.; Tolderlund, D. S. 1972. Distribution and ecology of living planktonic Foraminifera in surface waters of the Atlantic and Indian Oceans. In: Funnell, B. M.; Riedel, R. (Eds.) The Micropaleontology of Oceans, Cambridge University Press, pp. 105–150.

Schiebel, R., Bijma, J., & Hemleben, C. (1997). Population dynamics of the planktic foraminifer Globigerina bulloides from the eastern North Atlantic Deep Sea Research Part I: Oceanographic Research Papers, 44 (9-10), 1701-1713 DOI: 10.1016/S0967-0637(97)00036-8

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Friday Fellow: Downy Mildew

by Piter Kehoma Boll

Last week I introduced a serious plant pathogen, the gray mold, that attacks many crops and has a special role as either a bad or a good guy in wine grapes. But a plant that is never happy with an infection by the gray mold is certainly the lettuce. And in this case our juicy vegetable has an enemy that makes it susceptible to the mold, and I’m bringing it to you today.

Named Bremia lactucae, this organism is a oomycete, thus belonging to a group of organisms that was formerly classified as a fungus, but that currently is known to be more closely related to brown and golden algae. This species attacks lettuces and closely related plants, causing a disease called downy mildew.

Bremia_lactucae

A lettuce leaf with downy mildew. Photo by Gerald Holmes.*

The downy mildew is the most important disease affecting lettuce worldwide. The disease itself is not the main problem, although it decreases the quality of the crop. Its main problem is that it makes the vegetable more vulnerable to other infections, such as those by the gray mold, and also increases the risk of contamination by human pathogens, such as intestinal parasites.

Bremia_lactucae1

A branch of the downy mildew under the microscope. Photo by Bruce Watt.*

The usual forms of controling the spread of the downy mildew is by using fungicides and developing mildew-resistant lettuces by hybridization with wild and naturally resistant varieties. However, as usual, the downy mildew eventually adapts to this, giving rise to fungicide-resistant strains, as well as strains able to neutralize the resistance of lettuce lineages. It’s one more evolutionary arms race.

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ResearchBlogging.orgReferences:

Beharav, A., Ochoa, O., & Michelmore, R. (2013). Resistance in natural populations of three wild Lactuca species from Israel to highly virulent Californian isolates of Bremia lactucae Genetic Resources and Crop Evolution, 61 (3), 603-609 DOI: 10.1007/s10722-013-0062-5

Parra, L., Maisonneuve, B., Lebeda, A., Schut, J., Christopoulou, M., Jeuken, M., McHale, L., Truco, M., Crute, I., & Michelmore, R. (2016). Rationalization of genes for resistance to Bremia lactucae in lettuce Euphytica, 210 (3), 309-326 DOI: 10.1007/s10681-016-1687-1

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