Fashionable testate amoebae!

Fashion phenomena strongly influence our societies. These phenomena mostly affect young people and can be very worrysome. Many sociological studies seek to understand these phenomena, based on community background, culture and society tendencies but none seem to have considered a simple possibility: are our young people not just copying nature?

Recently, a very interesting study highlighted an intriguing fashion phenomenon within the testate amoeba community. Gomaa et al. (1) indeed revealed that all mixotrophic testate amoebae dressed up with the same algal-underwear!

Mixotrophic testate amoebae are species able to combine two nutrition modes; phototrophy and phagotrophy (predation). Using light energy thanks to their algal symbionts, mixotrophic testate amoebae are able to fix inorganic carbon through photosynthesis, whilst in parallel they are also able to assimilate organic carbon by feeding on prey items such as bacteria, fungi and other protists (2-5). This mixotrophic energetic mode thus gives them an important trophic advantage when food resources are low.

Some mixotrophic testate amoebae we can find in mosses : Placocista spinosa (A), Archerella flavum (B), Amphitrema wrigthianum (C), Hyalosphenia papilio (D) and Heleopera sphagni (E). Scale bar on E = 50 μm

Figure 1| Some mixotrophic testate amoebae we can find in mosses : Placocista spinosa (A), Archerella flavum (B), Amphitrema wrigthianum (C), Hyalosphenia papilio (D) and Heleopera sphagni (E). Scale bar on E = 50 μm

Most mixotrophic testate amoebae show different characteristics, with for instance, different body sizes, shape and test composition. However, visually under the microscope, it seems that all of these species choose their algal symbionts in the same shop, copying each other! Probably intrigued by such fashion phenomena, Gomaa et al. (1) investigated the genetic diversity of the algal symbionts harboured by several mixotrophic testate amoeba species such as Archerella flavum, Hyalosphenia papilio, Heleopera sphagni and Placocista spinosa. These analyses showed that most algae found in testate shells shared the same kind of gene sequence (ribulose- 1,5-bisphosphate carboxylase/oxidase), thus revealing a close genetic proximity (1). The phylogenetic analysis further placed all surveyed testate amoebae symbionts close to Chlorella variabilis, a species known for forming symbiotic relationships with the ciliate Paramecium bursar (6). However, the authors also underlined that it is probable that some other endosymbiotic species occur in mixotrophic testate amoebae. Some symbionts morphologically clearly differ from C. variabilis in shape and colour, in particular within genus Placocista (Figure 1).

The modalities of symbiont acquisition by mixotrophic testate amoebae are still poorly kown and would require more investigations. Who is copying whom? Did Archerella flavum make Hyalosphenia papilio jealous with such nice colours in its shell leading the latter to feed on it to steal these nice coloured symbionts (Figure 2)? Is Placocista spinosa a weak copy of Archerella flavum and Hyalosphenia papilio, selecting its symbionts from a cheaper shop? Many questions remain unanswered. Could some of these require a sociological approach?

 

Hyalosphenia papilio taking its revenge on Archerella flavum H. papilio feeding on A. flavum.

Figure 2 | Hyalosphenia papilio taking its revenge on Archerella flavum.

 

References

  1. Gomaa, F. et al. One alga to rule them all: unrelated mixotrophic testate amoebae (amoebozoa, rhizaria and stramenopiles) share the same symbiont (trebouxiophyceae). Protist 165, 161–176 (2014).
  2. Gilbert, D., Amblard, C., Bourdier, G., Francez, A.-J. & Mitchell E. A. D. Le régime alimentaire des thécamoebiens (Protista, Sarcodina). L’année Biologique 39, 57–68 (2000).
  3. Gilbert, D., Mitchell, E. A. D., Amblard, C., Bourdier, G. & Francez, A.-J. Population dynamics and food preferences of the testate amoeba Nebela tincta major-bohemica-collaris complex (Protozoa) in a Sphagnum peatland. Acta protozoologica 42, 99–104 (2003).
  4. Jassey, V. E. J., Shimano, S., Dupuy, C., Toussaint, M.-L. & Gilbert, D. Characterizing the feeding habits of the testate amoebae Hyalosphenia papilio and Nebela tincta along a narrow ‘fen-bog’ gradient using digestive vacuole content and 13C and 15N isotopic analyses. Protist 163, 451–464 (2012).
  5. Wilkinson, D. M. & Mitchell, E. A. D. Testate Amoebae and Nutrient Cycling with Particular Reference to Soils. Geomicrobiology Journal 27, 520–533 (2010).
  6. Hoshina, R., Iwataki, M. and Imamura, N. (2010) Chlorella variabilis and Micractinium reisseri sp nov (Chlorellaceae, Trebouxiophyceae): Redescription of the endosymbiotic green algae of Paramecium bursaria (Peniculia, Oligohymenophorea) in the 120th year. Phycological Research, 58, 188-201.

Hotel Testate Amoebae

Imagine, after a long journey, you arrive alone in a hotel. The radio is playing a nice song…

“On a dark desert highway, cool wind in my hair

Warm smell of colitas, rising up through the air

Up ahead in the distance, I saw a shimmering light

My head grew heavy and my sight grew dim

I had to stop for the night”

You’re lucky, all of the rooms are free, and you can choose the one you like. You try all of the rooms and choose the largest, most comfortable room, with the best view and a well-stocked fridge.

“Welcome to the Hotel Testate Amoebae

Such a lovely place (Such a lovely place)

Such a lovely face

Plenty of room at the Hotel Testate Amoebae

Any time of year (Any time of year)

You can find it here”

After some time, you realize you start getting bored alone in this hotel and call some friends to share your room and your fridge. Your friends delight greatly in your hotel and thus call their own friends to continue parties, reducing the space and resources available.

“They livin’ it up at the Hotel Testate Amoebae

What a nice surprise (what a nice surprise)”

You decide to move with your friends in another hotel, nicely situated in the mountains. Here again, the local food is great and parties abundant… decreasing food and drinks quickly after few weeks… Why not moving again? Seems a good choice and you move not so far in new hotel.

Just get in the hotel,     “You called up the Captain, ’Please bring me French red wine’

He said, ‘We haven’t had such wine here since nineteen sixty nine’

Some voices are calling from far away,

‘They only have Coca Cola there…’

Just to hear them say…”

What do you do? You have some good old whiskey in stock and therefore decide to mix it with Coca Cola… Unfortunately, this mixture is not good enough for your friends forcing them leaving one by one…

“Last thing I remember, they were

Running for the door…”

 What do testate amoebae do when different nutrient resources are available? This is the question posed by Krashevska et al. (2014). These authors found that testate amoebae from tropical mountain rainforests significantly responded to moderate nutrient additions. They investigated rainforests along an altitudinal transect to get insight into variations in the effects of nutrient inputs with altitude. They found that both diversity and density of testate amoebae benefited from the addition of N (e.g. French red wine), whereas the addition of P detrimentally affected their diversity and density (e.g. Whiskey-Coca Cola mixture). They also found that Nutrient-mediated changes in microbial PLFA community structure contributed only little to these changes, suggesting that testate amoebae communities are structured predominantly by abiotic factors rather than by the availability of food, but a more detailed analysis of microbial communities are needed to test these suggestions.

In conclusion, the results of Krashevska et al. suggest that testate amoebae communities of tropical mountain rainforests are structured by both positive and negative interactions via both biotic and abiotic factors, and that the response of testate amoebae to nutrient addition is dependent from altitude.

 

Krashevska, V., Sandmann, D., Maraun, M., & Scheu, S. (2014). Moderate changes in nutrient input alter tropical microbial and protist communities and belowground linkages, The ISME Journal 8(5), 1126–1134. [http://www.nature.com/ismej/journal/v8/n5/abs/ismej2013209a.html]

How shall I build my test?

How do testate amoebae build their tests? How they chose the components to build it? How do they assemble organic or inorganic particles that shape their shell? These are questions I’m often asked. Unfortunately, these questions are very difficult to answer using common tools like the light microscope.

During the last couple decades, testate amoebae have been increasingly used as proxies for reconstructing Holocene environmental change in peatlands. Community composition primarily reflects surface wetness and pH, and can be used to study mire development, climate change and human impacts. However, little is known regarding the factors that may alter quantitatively or qualitatively the test composition of these organisms. Recently studies observed variations in shell composition of some testate amoebae in acidic environments, and suggested that a better understanding of how testate amoebae build their test may improve paleo-reconstruction models (Mitchell et al. 2008).

Historically, many researchers have worked on characterizing the shell of testate amoebae (e.g., Moraczewski 1971, Netzel 1972, Saucin Meulenberg et al. 1973, Eckert et al. 1974, Stout & Walker 1976, Hedley et al. 1976, Golemansky & Couteaux 1982, Ogden 1980a, b, 1983, 1984). Unfortunately, this line of research on testate amoebae has diminished over time.

Structural variability of the shell of testate amoebae (Source; Maxence Delaine)

Structural variability of the shell of testate amoebae (Source; Maxence Delaine)

So, when I heard that a PhD student – Maxence Delaine – had recently worked on this topic in France I was very curious. To satisfy my curiosity, I met Maxence Delaine and he explained me what they found in their recent paper (Armynot du Chatelet et al. 2013).

Across 14 sites situated in north-eastern France, Maxence collected samples from different microhabitats, such as mosses and soil, to study variations in testate amoeba shell composition.

Sites sampled for determination of shell construction of testate amoebae

Sites sampled for determination of shell construction of testate amoebae

3D representation of one species of testate amoebae, Difflugia oblonga. This picture is obtained by numerical recombination and correction of numerous 2D slides which are given by X-Ray microtomography. We can see on this picture the variability of the numerous grains constituting the shell: small vs big or smooth vs angular particules. (Source Maxence Delaine)

3D representation of one species of testate amoebae, Difflugia oblonga.
This picture was obtained by numerical recombination and correction of numerous 2D slides which are given by X-Ray microtomography.  The picture highlights the variability of the grains constituting the shell: small vs big or smooth vs angular particules. (Source Maxence Delaine)

The authors explored the potential application of 3D X-ray micro-tomography in addition to 2D techniques (Environmental Scanning Electron Microscope, Electron Probe Micro-Analysis, and cathodoluminescence) to characterize specimens such as Difflugia oblonga. The goal of this work was to test whether 3D morphology of testate amoebae in aqueous environments was governed by sediment size distribution and mineralogical composition.

From the 3D images, the authors calculated different parameters characterising the geometry of the specimens (size and mass) and of the individual grains forming the specimen (grain size distribution and volume). Combining chemical, mineralogical and morphological analyses allowed them to compare the grains forming the test with those of the sediment. Surprisingly, they found that Difflugia oblonga selectively picked up the small size fraction of the sediment with a preference for low-density silicates close to quartz density (~2.65). They also found that the maximum-sized grains are used for the pseudostome (i.e. shell aperture).

The following diagram shows that Difflugia oblonga is able to select the grains based on size, because the grain-size of the sediment is completely different from the grain-size of the particles constituting these amoeba shells. Moreover, no particles exceed the limit ‘‘αβ’’, which corresponds to the maximal measured size of the pseudostome of these 2 individuals. It seems likely that all the particles must pass through the pseudostome before being distributed by the amoeba for the shell’s construction.

Histograms of the particles size which constitute the shell of 2 individuals (Difflugia oblonga), compared to the grain-size curve of the sediment (in which these amoebae lived).

Histograms of the particles size which constitute the shell of 2 individuals (Difflugia oblonga), compared to the grain-size curve of the sediment (in which these amoebae lived).

Amazing isn’t it? A single-celled organism selecting the “bricks” for its house! Research on this topic is very promising, and these results highlight that there is still much to learn shell composition of these amazing organisms.

References

ARMYNOT DU CHATELET E., NOIRIEL C., DELAINE M. (2013). 3D morphological and mineralogical characterisation of testate amoebae.  – Microscopy and Microanalysis, 19, 1511-1522.

ECKERT B.S., MCGEE-RUSSELL S.M., 1974, Shell structure in Difflugia lobostoma observed by scanning and transmission electron microscopy. – Tissue & Cell, 6, 215-221.

HEDLEY R.H., OGDEN C.G. & MORDAN N.J., 1976, Manganese in the shell of Centropyxis (Rhizopodea: Protozoa). – Cell Tiss. Res., 171, 543-549.

GOLEMANSKY V. & COUTEAUX M.M., 1982, Etude en microscopie électronique à balayage de huit espèces de thécamœbiens interstitiels du supralittoral marin. – Protistologica, 18, 473-480.

MITCHELL E.A.D., PAYNE R.J & LAMENTOWICZ M., 2008, Potential implications of differential preservation of testate amœba shells for paleoenvironmental reconstruction in peatlands, – J. Paleolimnol., 40, 603-618.

MORACZEWSKI J., 1971a, La composition chimique de la coque de Arcella discoides Ehrbg. – Acta Protozool., 8, 407-422.

NETZEL H., 1972, Die schalenbildung bei Difflugia oviformis (Rhizopoda, Testacea). – Z. Zellforsch, 135, 55-61.

STOUT J. D. & WALKER G. D., 1976, Discrimination of mineral particles in test formation by thecamœbae. – Trans. Amer. Micros. Soc., 95, 486-489.

OGDEN C.G. & HEDLEY R.H., 1980a, An atlas of freshwater testate amœbæ, Oxford University Press, 113 p.

OGDEN C.G., 1980b, Shell structure in some pyriform species of Difflugia (Rhizopodea). – Arch. Protistenk., 123, 455-470.

OGDEN C.G., 1983, Observations on the systematics of the genus Difflugia in Britain. – Bull. Br. Mus. Nat. Hist. (Zool.), 44, 1-73.

OGDEN C.G., 1984, Shell structure of some testate amœbæ from Britain (Protozoa, Rhizopoda). – Journal of Natural History, 18, 341-361.