Category Archives: protists

Friday Fellow: Toxo

by Piter Kehoma Boll

If I had to bet on a parasite that you who are reading this probably have in your body, I’d go for today’s fellow, the protist Toxoplasma gondii, sometimes simply called toxo.

Found worldwide, the toxo is one of the most common parasites in humans, with estimations that about half of the world’s population is infected. Fortunately, this creature usually occurs in a latent form and does not offer great risks, but eventually it may develop into a more serious condition called toxoplasmosis, especially in people with weakened immunity.

But let’s take a closer look at this tiny fellow.

Toxoplasma_gondii_oocyst

Oocysts of Toxoplasma gondii. This is the form found in the environment and that can start an infection in your body.

The toxo is a protist belonging to the phylum Apicomplexa, a group of parasitic alveolates that also includes the agent that causes malaria. Although traditionally considered a protozoan, the apicomplexans are closely related to dinoflagellates (which are generally considered as a group of algae). They have a unique organelle called apicoplast, which they use to penetrate a host cell. The apicoplast is derived from a plastid (such as the chloropast), so in a certain way we can say that the apicomplexans are algae that evolved into intracellular parasites!

Toxoplasma_gondii_tachy

Tachyzoites of Toxoplasma gondii stained with Giesma from the peritoneal fluid of a mouse.

The life cycle of the toxo is kind of complex. Let’s start with the inactive form called oocyst, which may be found in the environment. If a warm-blooded animal ingests an oocyst, it will “burst” inside the gut of the animal and release several “quick-moving” forms called tachyzoites. The tachyzoites invade almost any cell of the body and multiply asexually inside it until the cell dies and release them, allowing them to infect more and more cells. When invading the brain, liver and muscles, the tachyzoites usually differentiate into cysts that become inactive. In this stage, the only thing that the toxo wants is that a cat (any species of the family Felidae) eats the host. It may even change the host’s behavior in order to make it bolder and more easily accessible to predators.

Toxoplasma_gondii_cyst

A cyst of Toxoplasma gondii that forms in the muscles, brain and liver of any warm-blooded anymal. All the cyst wants is to be eaten by a cat!

Now let’s assume that a cat ate the host (that was likely a bird or mouse). Inside the cat’s gut, the cyst burst and releases several “slow-moving” forms called bradyzoites. This form invades the epithelial cells of the cat’s intestine and multiply asexually inside them. Eventually, the bradyzoites differentiate into either tachyzoites or gametocytes (sperm- and egg-like cells). When two gametocytes fuse, they form a zygote that matures into an oocyst and is released into the environment, restarting the cycle.

Toxoplasma_life_cycle

The complex life cycle of Toxoplasma gondii. Credits to Mariana Ruiz Villarreal.

As always, the lifecycle of parasites is a wonderful adventure!

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ResearchBlogging.orgReferences:

Tenter, A., Heckeroth, A., & Weiss, L. (2000). Toxoplasma gondii: from animals to humans International Journal for Parasitology, 30 (12-13), 1217-1258 DOI: 10.1016/S0020-7519(00)00124-7

Wikipedia. Toxoplasma gondii. Available at <https://en.wikipedia.org/wiki/Toxoplasma_gondii&gt;. Access on March 6, 2017.

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Friday Fellow: Crawling Spider Alga

by Piter Kehoma Boll

The world of unicelular creatures includes fascinating species, some of which were already presented here. And today one more is coming, the marine phytoplanctonic amoeboid protist Chlorarachnion reptans, which again is a species without a common name, so I created one: crawling spider alga.

chlorarachnion_reptans

A plasmodium of the crawling spider alga Chlorarachnion reptans. Photo by Wikimedia user NEON.*

The crawling spider alga was dicovered in the Canary Islands in 1930. It is an amoeboid alga that forms plasmodia (multinucleated networks) of cells connected by thin strips of cytoplasm (reticulopodia). The reticulopodia are also used to capture prey (bacteria and smaller protists, especially algae) working kind of like a spider web. Additionally, the crawling spider alga has chloroplasts, so being able to conduct photosynthesis. It is, therefore, a mixotrophic organism, having more than one way of feeding.

The chloroplasts of the crawling spider alga, as well of other species in its group, called Chlorarachniophyceae, have four membrane layers and appears to have evolved from a green alga that was ingested and became an endosymbiont. As a result, the chloroplast of the crawling spider alga has two sets of DNA, one from the original chloroplast that came from an endosymbiotic cyanobacteria (located inside the inner membrane) and one of the green algae (between the two inner and the two outer membranes).

Although traditionally seen as a group of algae, the chlorarachniophytes are not closely related to the more “typical” algae, such as red, green, brown and golden algae or diatoms. They are actually relatives of other protists with thin net- or thread- like pseudopods, such as radiolarians and foraminifers, forming with them the group Rhizaria.

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ResearchBlogging.orgReferences:

AlgaeBase. Chlorarachnion reptans Geitler. Available at <http://www.algaebase.org/search/species/detail/?species_id=59340&gt;. Access on March 5, 2017.

EOL – Encyclopedia of Life. Chlorarachnion reptans. Available at <http://eol.org/pages/897235/overview&gt;. Access on March 5, 2017.

Hibberd, D., & Norris, R. (1984). Cytology and ultrastructure of Chlorarachnion reptans (Chlorarachniophyta divisio nova, Chlorarachniophyceae classis nova) Journal of Phycology, 20 (2), 310-330 DOI: 10.1111/j.0022-3646.1984.00310.x

Ludwig, M., & Gibbs, S. (1989). Evidence that the nucleomorphs of Chlorarachnion reptans (Chloraracnhiophyceae) are vestigial nuclei: morphology, division and DNA-DAPI fluorescence Journal of Phycology, 25 (2), 385-394 DOI: 10.1111/j.1529-8817.1989.tb00135.x

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Friday Fellow: Divergent Dinobryon

by Piter Kehoma Boll

Let’s return once more to the troublesome and neglected protists. This time I’m bringing you another tiny but beautiful alga, more precisely a golden alga. Its name is Dinobryon divergens and as usual there is no common name, so I invented one by simply translating the scientific name, thus I’ll call it the divergent dinobryon.

The divergent dinobryon is part of the class Chrysophyceae, commonly known as golden algae. Measuring about 50 µm in length, it lives in temperate lakes around the world and forms colonies composed of about 6 to 50 ovoid cells that are surrounded by a vase-like shell (lorica) of cellulose, as seen in the picture below.

dinobryon_divergens

A branching colony of Dinobryon divergens. The cells are clearly visible inside the lorica. Photo by Frank Fox.*

During colony formation, an original cell divides and one of the two daughter cells slides to the opening of the lorica and starts to construct a new one. It starts by creating the base of the lorica, which has a funnel shape and is attached to the inner wall of the original lorica. With further divisions, the colony starts to grow in a tree-like form. And the most interesting part is that the cells have two flagella and use them to swim, pulling the whole colony through the water.

As with other golden algae, the divergent dinobryon produces an internal siliceous structure that is globose, hollow and has a single opening connecting to the outside. This structure is called a statospore or stomatocyst and allows the cell to enter a resting state (cyst). The statospore is an important structure to help distinguish different species of golden algae.

The divergent dinobryon is a mixotrophic organism, meaning that it feeds by photosynthesis and by ingesting food too, especially bacteria. Kind of an interesting fellow, don’t you think?

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ResearchBlogging.orgReferences:

Franke, W., & Herth, W. (1973). Cell and lorica fine structure of the chrysomonad alga, Dinobryon sertularia Ehr. (Chrysophyceae) Archiv für Mikrobiologie, 91 (4), 323-344 DOI: 10.1007/BF00425052

Herth, W. (1979). Behaviour of the chrysoflagellate alga, Dinobryon divergens, during lorica formation Protoplasma, 100 (3-4), 345-351 DOI: 10.1007/BF01279321

Karim, A., & Round, F. (1967). Microfibrils in the lorica of the freshwater alga Dinobryon New Phytologist, 66 (3), 409-412 DOI: 10.1111/j.1469-8137.1967.tb06020.x

Sandgren, C. (1981). Characteristics of sexual and asexual resting cyst (statospore) formation in Dinobryon cylindricum Imhof (Chrysophyta) Journal of Phycology, 17 (2), 199-210 DOI: 10.1111/j.1529-8817.1981.tb00840.x

Sheath, R., Hellebust, J., & Sawa, T. (1975). The statospore of Dinobryon divergens Imhof: Formation and germination in a subarctic lake Journal of Phycology, 11 (2), 131-138 DOI: 10.1111/j.1529-8817.1975.tb02760.x

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Friday Fellow: B. coli

by Piter Kehoma Boll

It’s time to give more space for parasites, including human parasites! So today our fellow comes right from the stool of many mammals, including humans. Its name is Balantidium coli, or B. coli for short.

B. coli is a ciliate, i.e., a member of the phylum Ciliophora, a group of protists that have their cells covered by cilia, which are nothing more than very short and numerous flagella. Most ciliates are free-living organisms, and in fact B. coli is the only ciliate known to be harmful to humans, but not only to humans. Many other mammals are also known to host this fellow, especially pigs.

balantidium_coli

The red elongate macronucleus of B. coli makes it look like a bad guy, don’t you think? Photo extracted from http://www.southampton.ac.uk/~ceb/Diagnosis/Vol2.htm

The typicall habitat of B. coli is the large intestine of mammals. The protist lives there in an active phase called trophozoite (seen in the image above) and feeds on the natural bacteria that live in the gut. When facing dehydration, which happens in the final portion of the intestine or after the organism is released with the feces, B. coli changes to an inactive phase called cyst, which is smaller than the trophozoite and covered by a thick wall. The cysts released in the environment may be ingested by a new host and reach their intestine, where they will return to the trophozoite form.

balantidium_coli2

A cyst of B.coli. Photo extracted from http://www.southampton.ac.uk/~ceb/Diagnosis/Vol2.htm

Symptoms of infection by B. coli, also known as balantidiasis, include explosive diarrhea every 20 minutes and, in acute infections, it may cause perforation of the colon and become a life-threatening condition.

Fortunately, infection in humans is not that common. The most affected country nowadays are the Philippines, but you may get infected anywhere. The best way to reduce the infection risks is by having good sanitary conditions and personal hygiene. However, as pigs are the most common vectors of the disease, it will likely continue to exist as long as humans raise pigs.

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ResearchBlogging.orgReferences:

Schuster, F., & Ramirez-Avila, L. (2008). Current World Status of Balantidium coli Clinical Microbiology Reviews, 21 (4), 626-638 DOI: 10.1128/CMR.00021-08

Wikipedia. Balantidium coli. Available at <https://en.wikipedia.org/wiki/Balantidium_coli&gt;. Access on February 23, 2017.

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Friday Fellow: Northern Plaited Radiolarian

by Piter Kehoma Boll

Some weeks ago I introduced a diatom here and mentioned that, despite the fact that they are a very abundant group, little information on species is available. Today our species is a radiolarian and, just as with the diatoms, they are abundant but little known.

I struggled to find an extant species that also had a good and available photo to share. And the winner was a species known as Cleveiplegma boreale, or Rhizoplegma boreale perhaps. I’m not sure what is the currently accepted name. Anyway, it does not have a common name, but I decided to create one, so let’s call it “northern plaited radiolarian”.

Radiolarians are unicelular organism that have an intricate mineral skeleton that contains a central capsule that typically divides the cell into two portions: an inner one and an outer one. Our fellow today looks like this:

cleveiplegma_boreale

A living specimen of the northern plaited radiolarian. Photo by John Dolan.*

The northern plaited radiolarian has from 6 to 10 spines growing out of it and there is a complex plaited pattern of the skeleton that surrounds them and the inner shell. Measuring anout 20µm in diameter, it is a rather large radiolarian.

Although it is known from fossils along the Quaternary, from at least 10 thousand years before present, the northern plaited radiolarian is still a living species. Currently it is known to occur in the Nordic Seas, around Scandinavia, Iceland and Greenland, in the North Pacific, including the Bering Sea, and in the Southern Ocean, around Antarctica. We can see, therefore, that this species likes cold waters.

Ah, and they feed on diatoms… I guess.

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ResearchBlogging.orgReferences:

Dolven, J., & Bjørklund, K. (2001). An early Holocene peak occurrence and recent distribution of Rhizoplegma boreale (Radiolaria): a biomarker in the Norwegian Sea Marine Micropaleontology, 42 (1-2), 25-44 DOI: 10.1016/S0377-8398(01)00011-1

Dumitrica, P. (2013). Cleveiplegma nov. gen., a new generic name for the radiolarian species Rhizoplegma boreale (Cleve, 1899) Revue de Micropaléontologie, 56 (1), 21-25 DOI: 10.1016/j.revmic.2013.01.001

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Friday Fellow: Wheel Necklace Diatom

ResearchBlogging.orgby Piter Kehoma Boll

Most of you likely know what diatoms are, microscopic algae with a silica shell that are very abundant in the world’s oceans and one of the main oxygen producers. You may have seen images like the one below, showing the diversty of diatoms, but can you name a single species?

diatoms

The beautiful, yet largely neglected by non-experts, diversity of diatoms. Photo by Wikimedia user Wipeter.*

Today I decided to bring you a diatom Friday Fellow and let me tell you: it was not at all easy to select a nice species with a considerable amount of available information and a good picture. But at the end the winner of the First Diatom Friday Fellow Award was…

Thalassiosira rotula!

thalassiosira_rotula

Three connected individuals of Thalassiosira rotula. Photo by micro*scope.**

As with most microorganisms, this species has no common name and, as it is a tradition here, I decided to make one up and chose wheel necklace diatom. Necklace diatom seems to be a good common name for species in the genus Thalassiosira, as they are formed by several individuals connected to each other in a pattern that resembles a necklace. I decided to call this particular species wheel necklace diatom because of its specific epithet, rotula, which means little wheel in Latin.

The wheel necklace diatom is a marine species found worldwide close to the coast. It is very abundant and the dominant species in some areas, so it is of great ecological importance. Small planctonic crustaceans, such as copepods, usually feed on the wheel necklace diatom and, as those crustaceans are used as food for much larger animals, the wheel necklace diatom is responsible for sustaining a whole food chain.

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References:

Ianora, A., Poulet, S., Miralto, A., & Grottoli, R. (1996). The diatom Thalassiosira rotula affects reproductive success in the copepod Acartia clausi Marine Biology, 125 (2), 279-286 DOI: 10.1007/BF00346308

Krawiec, R. (1982). Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light, temperature and salinity Marine Biology, 69 (1), 79-89 DOI: 10.1007/BF00396964

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Friday Fellow: Tepid ammonia

by Piter Kehoma Boll

One of the few groups of living being not yet featured in Friday Fellow is Rhizaria, a group of single-celled organisms that includes the famous foraminifers. So today I decided to bring you just that, a foraminifer. And I think a good species to start with is Ammonia tepida, or the “tepid ammonia” as I decided to call it.

A live Ammonia tepida. Credits to Scott Fay.*

A live Ammonia tepida. Credits to Scott Fay.*

The tepid ammonia is found worldwide in brackish waters, or more precisely in the sediments deposited in brackish waters worlwide. It is able to tolerate a wide range of temperatures and degrees of salinity and is considered an ideal species of laboratory studies. As most foraminifers, the tepid ammonia secrets a shell of calcium carbonate, which is deposited on the cell’s surface in the form of a chain of chambers forming a spiral path, thus making it look like a snail shell.

Living in the sediments, the tepid ammonia feeds mainly on algae, but also consumes bacteria. In the laboratory, it demonstrated to have the ability to prey on small animals, such as nematodes, copepods and molluk larvae.

This kid got talent!

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References:

Dupuy, C.; Rossignol, L.; Geslin, E.; Pascal, P.-Y. (2010) Predation of mudflat meio-macrofaunal metazoans by a calcareous foraminifer, Ammonia tepida (Cushman, 1926). The Journal of Foraminiferal Research 40 (4): 305–312.

Munsel, D.; Kramar, U.; Dissard, D.; Nehrke, G.; Berner, Z.; Bijma, J.; Reichart, G.-J.; Neumann, T. (2010) Heavy metal incorporation in foraminiferal calcite: results from multi-element enrichment culture experiments with Ammonia tepida. Biogeosciences 7 (8): 2339–2350.

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