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.

Testate amoebae on fire

Contributed by Katarzyna Marcisz

How do testate amoeba communities respond to fire? How does burning affect this group of microorganisms and the environment where they occur in exceptionally high abundance – Sphagnum peatlands?

Answering these questions is crucial, as fire has a significant impact on peatland ecosystems. Peatlands are an important carbon pool, containing 1/3 of the global soil carbon (Parish et al., 2008). It has been shown that even a moderate drop in water table influences vegetation composition in peatlands and disturbs carbon accumulation (Kettridge et al., 2015). Peatlands experiencing drying are also more often ignited, and the frequency of fire and the extent of peat fires often increases (Turetsky et al., 2015). Peat fires can be deceptive: peat often burns by smouldering combustion that can persist for long periods of time rather than by more visible large fires as in the case of forests. The consequence is nevertheless that this burning affects the peat carbon stock.

The relationships between testate amoebae and fire are still quite a mystery. In studies from North America, Clifford and Booth (2013) and Clifford and Booth (2015) revealed peaks in microscopic charcoal accumulation rates that corresponded to drought periods as reconstructed with the use of a testate amoeba-based transfer function. However, these charcoal peaks were likely primarily derived from regional, upland fires rather than fire on the peatlands themselves. The effects of peatland fires on testate amoeba communities, and the response of individual species, have not been adequately examined. For example, Trigonopyxis arcula was suggested to be a possible fire indicator by Warner (1990) and Turner et al. (2014), and Hyalosphenia subflava was correlated with fire in the work by Turner and Swindles (2012). However, Turner et al. (2014) later suggested it should rather not be regarded as a reliable local fire indicator.

Fig. 1. Linje mire in the spring 2013.

Fig. 1. Linje mire in the spring 2013.

Recently the relationships between individual testate amoeba species and fire were examined in a study by Marcisz et al. (2015), which was conducted within the RE-FIRE Sciex project (http://www.swissuniversities.ch/en/topics/sciex) and CLIMPEAT project (www.climpeat.pl), in northern Poland at a beautiful Linje mire (Fig. 1).

The analyses revealed that the peatland was wet before the onset of the Little Ice Age (ca. AD 1300-1850), when a rapid drop in water table occurred. Drying was also correlated with human migrations in the region, and with changing agricultural practices. Anthropogenic fires preceded hydrological changes on the mire; the response of the mire recorded as hydrological changes towards drier conditions was delayed in relation to the surrounding fire-related vegetation changes.

Fig. 2. Cross-correlation diagrams between testate amoeba species and macroscopic charcoal particles (from Marcisz et al., 2015)

Fig. 2. Cross-correlation diagrams between testate amoeba species and macroscopic charcoal particles (from Marcisz et al., 2015)

Individual testate amoeba species were correlated with macroscopic charcoal particles recorded in the peat profile (Fig. 2). Testate amoebae indirectly responded to vegetation removal in the catchment driven by fire. While all the wet indicator species were negatively correlated with fire activity, most of the dry indicators (as well as Arcella discoides) were positively correlated. Although no explicit local fire indicator was found, from all the testate amoeba species Nebela tincta s.l. had the highest positive correlation recorded (Fig. 3)…..

https://www.youtube.com/watch?v=J91ti_MpdHA&feature=youtu.be&t=46s

Fig. 3. Nebela tincta s.l. on fire.

Fig. 3. Nebela tincta s.l. on fire.

Additional work is needed to better quantify the relationships between testate amoebae, hydrological change, and fire, and experimental work is needed to assess the causes of these relationships. Such work may provide insight into the underlying processes controlling microbial community responses to fire and hydrological change. However, fire activity likely affects peatland microbial food webs, both directly (combustion of surface Sphagnum and peat layers) and indirectly (surrounding vegetation and surface run-off changes).

Literature cited

Clifford, M.J., Booth, R.K., 2013. Increased probability of fire during late Holocene droughts in northern New England. Climatic Change 119, 693–704.

Clifford, M.J., Booth, R.K., 2015. Late-Holocene drought and fire drove a widespread change in forest community composition in eastern North America. The Holocene 25, 1102-1110.

Kettridge, N., Turetsky, M.R., Sherwood, J.H., Thompson, D.K., Miller, C.A., Benscoter, B.W., Flannigan, M.D., Wotton, B.M., Waddington, J.M., 2015. Moderate drop in water table increases peatland vulnerability to post-fire regime shift. Scientific Reports 5.

Marcisz, K., Tinner, W., Colombaroli, D., Kołaczek, P., Słowiński, M., Fiałkiewicz-Kozieł, B., Łokas, E., Lamentowicz, M., 2015. Long-term hydrological dynamics and fire history over the last 2000 years in CE Europe reconstructed from a high-resolution peat archive. Quaternary Science Reviews 112, 138-152.

Parish, F., Sirin, A., Charman, D.J., Joosten, H., Minayeva, T., Silvius, M., Stringer, L., 2008. Assessment on peatlands, biodiversity and climate change: main report. Global Environment Centre, Kuala Lumpur and Wetlands International, Wageningen 179 pp.

Turetsky, M.R., Benscoter, B., Page, S., Rein, G., van der Werf, G.R., Watts, A., 2015. Global vulnerability of peatlands to fire and carbon loss. Nature Geosci 8, 11-14.

Turner, T.E., Swindles, G.T., 2012. Ecology of Testate Amoebae in Moorland with a Complex Fire History: Implications for Ecosystem Monitoring and Sustainable Land Management. Protist 163, 844-855.

Turner, T.E., Swindles, G.T., Roucoux, K.H., 2014. Late Holocene ecohydrological and carbon dynamics of a UK raised bog: impact of human activity and climate change. Quaternary Science Reviews 84, 65-85.

Warner, B.G., 1990. Testate amoebae (Protozoa). Methods in Quaternary ecology no. 5. Geosci. Can. 5, 65-74.

Testate amoebae and their influence on (global) silicon cycling

Contributed by Daniel Puppe

Silicon is the second most common element in the Earth’s crust (after oxygen) and the seventh most abundant element in the universe. That means we can find silicon almost everywhere. Silicon plays a pivotal role in diverse living organisms comprising pro- and eukaryotes accumulating biogenic silicon in various siliceous structures (= biosilicification) – like idiosomic testate amoeba shells. In soils of terrestrial ecosystems we can find a lot of biogenic silicon forming different silicon pools. These pools can be separated into zoogenic, phytogenic, microbial and protistic ones (Fig. 1).

Fig. 1: Biogenic silicon (Si) pools in terrestrial ecosystems (from Puppe et al. 2015).

Fig. 1: Biogenic silicon (Si) pools in terrestrial ecosystems (from Puppe et al. 2015).

While scientific research has been focused especially on the phytogenic silicon pool (represented by so-called phytoliths), little is known about zoogenic, microbial and protistic silicon pools. The protistic silicon pool in soils comprises mainly terrestrial diatoms and idiosomic testate amoebae (some testates are shown in Fig. 2).

Fig. 2: Scanning electron microscope (SEM) micrographs of various idiosomic (a - c) and xenosomic (d) testate amoebae: a) Euglypha rotunda-like amoeba, b) Puytoracia bonneti (first record for Germany), c) Corythion dubium and d) two individuals of Centropyxis sphagnicola. Scale bars in all micrographs = 20 µm. Source: Puppe et al. 2014.

Fig. 2: Scanning electron microscope (SEM) micrographs of various idiosomic (a – c) and xenosomic (d) testate amoebae: a) Euglypha rotunda-like amoeba, b) Puytoracia bonneti (first record for Germany), c) Corythion dubium and d) two individuals of Centropyxis sphagnicola. Scale bars in all micrographs = 20 µm. Source: Puppe et al. 2014.

However, what is the relevance of biogenic silicon pools for silicon cycling? To understand this, we have to look at biogeochemical cycles at a global scale. Globally, silicon and carbon cycles are connected by weathering processes and fluxes of dissolved silicon from terrestrial to aquatic ecosystems (e.g. Sommer et al. 2006). When silicon is washed away into the oceans, it is used by marine diatoms for frustule synthesis (frustules are the siliceous cell walls of diatoms). Due to their worldwide distribution in very high abundances, diatoms are able to fix carbon dioxide (CO2) on a large scale (about 20 % of the photosynthesis on Earth is carried out by diatoms! See, e.g., Armbrust 2009). By consuming atmospheric CO2, diatoms thus have an effect on climate change, which is mainly caused by increasing atmospheric concentrations of the greenhouse gas CO2 since 1750 (IPCC 2013). The fluxes of dissolved silicon are affected by organisms that synthesize siliceous structures and consequently accumulate and recycle biogenic silicon in soils. In other words, the more silicon that is fixed in terrestrial ecosystems, the less silicon that arrives in the oceans, and as a consequence diatom production in the oceans decreases. Let´s visualize the main aspects of the processes described so far (Fig. 3).

Fig. 3: Connections of global silicon (Si) and carbon (C) cycles and the influence of biogenic silicon pools (see descriptions in the text).

Fig. 3: Connections of global silicon (Si) and carbon (C) cycles and the influence of biogenic silicon pools (see descriptions in the text).

In two recent publications we analyzed protozoic silicon pools (represented by idiosomic testate amoebae) in initial (Puppe et al. 2014) and forested (Puppe et al. 2015) ecosystems. We found, that after (only!) 10 years of development idiosomic silicon pools in initial ecosystem states become comparable to the ones in forested ecosystems. In forest soils idiosomic silicon pools were relatively small (0.2 kg – 4.7 kg silicon per hectare in the upper 5 cm). Due to the fact that only intact shells were enumerated in our studies idiosomic silicon pools might be larger than calculated. However, there is no information on the quantity of this “platelet silicon pool”.

At the forested sites we further analyzed potential influences of abiotic factors (e.g. soil pH) and earthworms on idiosomic silicon pools. Surprisingly, no relationship between silicon supply (readily-available silicon in soils) and idiosomic silicon pools could be found, thus no silicon limitation for shell synthesis appeared in the field. Instead, idiosomic silicon pools showed a strong, negative relationship to earthworm biomasses. We concluded that earthworms control idiosomic silicon pools by direct (e.g. competition in the soil food web) and/or indirect mechanisms (e.g. change of habitat structure through burrowing activities). Earthworms themselves were strongly influenced by soil pH. Due to the fact that soil pH is a result of weathering and acidification, idiosomic silicon pools are indirectly, but ultimately controlled by soil forming factors, mainly parent material and climate. These results point to the potential relationships between soil fauna and the storage of biogenic silicon in terrestrial ecosystems. However, further research is needed to enlighten the complex biotic linkages in terrestrial biogeochemical silicon cycling and their importance for global silicon fluxes.

Annual biosilicification rates of living testate amoebae (17 kg – 80 kg silicon per hectare) in forested ecosystems were comparable to or even exceeded reported data of annual silicon uptake by trees. Just imagine it! Unicellular, microscopic organisms can out-compete multicellular, macroscopic ones in terms of annual silicon uptake. Given the worldwide distribution of testate amoebae, the importance of idiosomic silicon pools and corresponding biosilicification for (global) silicon cycling becomes clear.

Literature Cited

Armbrust, E.V. (2009). The life of diatoms in the world’s oceans. Nature, 459, 185-192.

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.

Puppe, D., D. Kaczorek, M. Wanner & M. Sommer (2014). Dynamics and drivers of the protozoic Si pool along a 10-year chronosequence of initial ecosystem states. Ecological Engineering 70, 477-482.

Puppe, D., O. Ehrmann, D. Kaczorek, M. Wanner & M. Sommer (2015). The protozoic Si pool in temperate forest ecosystems – Quantification, abiotic controls and interactions with earthworms. Geoderma 243-244, 196-204.

Sommer, M., D. Kaczorek, Y. Kuzyakov & J. Breuer (2006). Silicon pools and fluxes in soils and landscapes – a review. Journal of Plant Nutrition and Soil Science 169, 310-329.

Flying amoebae

Contributed by Edward A. D. Mitchell

Laboratory of Soil Biology, University of Neuchâtel

I’m learning to fly but I ain’t got wings

Coming down is the hardest thing

Jeff Lynne/ Tom Petty

Since the early days of protistology it has been known that testate amoebae can be transported passively by wind. Darwin had collected dust that had fallen on the Beagle while sailing off the coast of Africa. He sent the sample to Ehrenberg who observed it under his microscope and found many protists (Darwin, 1846). Observations such as this have led to the idea that microscopic organisms could travel far and colonise all potentially favourable habitats (i.e. everything is everywhere, but, the environment selects; (Baas Becking, 1934, de Wit and Bouvier, 2006)). It is therefore perhaps surprising that not much experimental research has been done to quantify the amoebae that are transported by wind. A recent modelling study showed that the medium to large sized testate amoebae (i.e. 40-60µm diameter) were unlikely to travel over large distances and certainly incapable of crossing oceans while the smaller ones (e.g. 9 µm diameter) could potentially do so (Wilkinson et al., 2012). But, to my knowledge, observational and experimental studies on wind dispersal of testate amoebae are very rare. An elegant recent study by Wanner and colleagues contributed to filling this important gap (Wanner et al., 2015).

Wanner and colleagues used sticky traps: 15cm diameter plastic petri dishes in which filter paper was attached using a paraffin-based balm, which also covered the filters. The petri dishes were used as passive, sticky traps for airborne organisms and contained no growth media. The system was initially designed to study seed dispersal but proved to also be useful to study microorganisms. They exposed traps for periods ranging from 16 to 42 days and recorded 12 testate amoeba species (excluding unidentifiable specimens): Centropyxis aerophila, C. elongata, C. sphagnicola, C. ambigua, C. eurystoma, Difflugia lucida, Phryganella acropodia, Tracheleuglypha dentata, Trigonopyxis arcula, Trinema complanatum, Trinema lineare, and Trinema penardi. The two most commonly found species were respectively ca. 40µm and 60µm in diameter (Phryganella acropodia and Centropyxis sphagnicola). The overall abundance was low with little over 80 specimens recorded in total. Therefore although this study shows that amoebae can “fly”, they don’t do so in massive numbers even close to the ground and near source populations. The probability for long-distance (e.g. across 100-1000km of ocean) passive dispersal must therefore be extremely low.

Also it is rather surprising that the dominant taxa recorded on the traps were not small euglyphids but mid-size arcellinids. Indeed small euglyphids are likely to be more numerous in the upper soil horizons and the better drained and exposed microsites from which they can be expected to have more chances to be lifted up by the wind. Their small size and lighter shells should potentially allow them to be transported more easily than larger taxa, but this is not what Wanner and colleagues observed.

Extrapolating form their results, Wanner and colleagues estimated that on average 61 individual amoebae (living + dead) were deposited per square meter each day. Therefore a viable population can become established rather rapidly on a newly exposed surface, provided that a source population is present nearby. These results also suggest that initial colonisation will be rather stochastic but that as more and more amoebae are deposited on a given place the full potential community will soon be present and community composition will therefore soon be controlled by local processes such as environmental filtering. The authors estimated that the shift from stochastic to deterministic community pattern takes place after ca. seven years of soil development and therefore concluded that testate amoebae are valuable indicators of initial ecosystem development and utilisation.

Such research is important at the local as well as global scales. Locally it informs on the mechanisms that determine primary and secondary colonisation of soil and other habitats and at which temporal scale testate amoebae can be used as bioindicators. Globally it provides useful data on actual wind dispersal of amoebae. The first step is indeed for an amoeba to become airborne and this may not be trivial depending where the species live.

The study of Wanner and colleagues also shows that it is not straightforward to design traps for studying aerial dispersal of testate amoebae. The traps were indeed initially not designed for such a study but were nevertheless useful. However it may be possible to develop an optimal type of trap for studying aerial dispersal of testate amoebae. This study clearly gives food for thoughts and hopefully will stimulate the community of testate amoeba researchers to further explore how amoebae colonise new habitats.

References

Baas Becking, L.G.M. (1934) Geobiologie of inleiding tot de milieukunde. W.P. Van Stockum & Zoon The Hague, the Netherlands.

Darwin, C. (1846) An account of the fine dust which often falls on vessels in the Atlantic Ocean. Quartely Journal of the Geological Society, 2, 26-30.

de Wit, R. & Bouvier, T. (2006) “Everything is everywhere, but, the environment selects”; what did Baas Becking and Beijerinck really say? Environmental Microbiology, 8, 755–758.

Wanner, M., Elmer, M., Sommer, M., Funk, R. & Puppe, D. (2015) Testate amoebae colonizing a newly exposed land surface are of airborne origin. Ecological Indicators, 48, 55-62.

Wilkinson, D.M., Koumoutsaris, S., Mitchell, E.A.D. & Bey, I. (2012) Modelling the effect of size on the aerial dispersal of microorganisms. Journal of Biogeography, 39, 89-97.

Tropical testate amoebae as hydrological indicators?

Sampling testate amoebae in a tropical peatland. A recent paper in Microbial Ecology by Swindles et al. suggests that testate amoebae have potential as hydrological indicators in tropical peatlands.

Sampling testate amoebae in a tropical peatland. A recent paper in Microbial Ecology by Swindles et al. suggests that testate amoebae have good potential as hydrological indicators in tropical peatlands.

Testate amoebae have been successfully used as indicators of past changes in peatland hydrology, particularly ombrotrophic (i.e., nutrients derived exclusively from precipitation) peatlands of north-temperate and boreal regions.  Over the past couple decades, many ecological studies of testate amoebae have been performed in these northern bogs, allowing empirical relationships between community composition and surface moisture to be described. Because the shells of testate amoebae preserve well in the acidic and anaerobic environment of bogs, these modern relationships have been used to infer past changes in the relative wetness of the bog surface from the composition of subfossil communities.  Much recent work has focused on the validation and interpretation of testate amoeba paleohydrological records from bogs, and their application to pressing global change questions.

Surveying along a transect across the peatland.

Surveying along a transect across the peatland.

However, very little is known regarding the potential paleoenvironmental applications of testate amoebae in tropical peatlands.  Peatlands in this region contain a large reservoir of soil carbon, and are extremely vulnerable to environmental changes including changes in land use (e.g., drainage, deforestation) as well as ongoing climate change. How have these peatlands responded to past environmental changes? How similar are communities of testate amoebae in these systems to those of northern bogs? Can testate amoebae be used as indicators of past hydrological changes in tropical peatlands? A recent study by Swindles et al. published in the journal Microbial Ecology set out to find preliminary answers to some of these questions.

One of 100 sampling sites.  Testate amoeba communities and several environmental variables were examined at each site.

Testate amoeba communities and several environmental variables were examined at 100 sites.

The study examined the present-day testate amoeba communities on a ombrotrophic peatland in Peruvian Amazonia. Surface samples of testate amoeba communities and measurements of water-table depth, pH, litter-moisture content, vegetation, and loss-on-ignition were taken along a transect across the peatland. The field work sounds like it was challenging, as the authors succinctly noted that the orientation of the transect had to be a bit flexible given certain obvious constraints:

A slight change in direction was needed half-way along the transect to avoid working in an area containing snakes.

Clearly the work was not well suited for ophidiophobes.

The research group also collected a peat core from the site and assessed changes in testate amoeba communities for the last several thousand years, using the results of their modern survey to inform their interpretation of the paleoecological record.

Tropical testates!

Tropical testates!

Results of the study indicated that the species composition of testate amoebae on this tropical peatland was most strongly related to measurements of water-table depth, with secondary relationships to pH. Forty-seven testate amoeba taxa were encountered, including one species only found in the southern hemisphere. Some taxa were clearly diagnotic of particular habitats (e.g., pools on the peatland surface). Testate amoebae were also preserved in the peat core,  and the authors applied the results of their modern study to infer changes in past water-table depth for approximately the last 3000 years. Although there is clearly much more work needed to describe the ecology of testate amoebae in peatland systems of the tropics, the results of this work indicate good potential to use testate amoebae in paleoenvironmental studies of these important, vulnerable, and unique peatland systems. Hopefully more work will follow soon.

 

 

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]

Testate amoeba CSI

Now here is something you don’t see everyday. In fact, I am pretty sure this has never been done before.  Ildiko Szelecz and colleagues set out to answer a question that very few of you must have already pondered: could testate amoebae be used in forensic studies?

This should in fact be a very ordinary question if you know something about soil biology and protists. A dead body is a huge influx of carbon and nutrients  into the soil that it is sitting atop.  The bacterial communities will basically go wild, and all of that must influence very heavily the community of eukaryotic microorganisms that used to inhabit there.  Interestingly enough, it appears that the idea of checking out what happens to testate amoebae communities has never popped into anyone’s head before.  Testate amoebae are abundant, somewhat easily recognizable micro-eukaryotes, which despite a few taxonomic issues are quite useful as indicators of environmental conditions.  Well, I think we have to thank Miss Szelecz for kindly looking into this gory issue!

Basically, the authors hung pig cadavers of approximately 20 kilos each in a nicely setup experiment.  For each pig replicate, there were two controls – a similar sized are with nothing in it, and an area where they added a plastic bag filled with 20 kg of soil to mimic possible micro-climatic effects that do not come form decomposition itself.  They then sampled soil from beneath the cadavers at regular intervals and counted testate amoebae – what could be more fun?

pig

What happens then is truly incredible.  At first, the testate amoebae die.  The changes introduced in soil chemistry are simply not tolerable to the amoebae and by the 22nd, all amoebae under the dead body are also dead.  The two controls behaved different from each other, presumably because microclimatic conditions (evaporation, etc) are quite different under a plastic bag filled with litter.

Screen Shot 2014-03-12 at 4.54.55 PMIn the image above straight from the paper, the plain line indicates live amoebae, the short-dashed line indicates encysted amoebae, and the long-dashed line indicates dead amoebae.

After the massive amoeba genocide caused by the dead pig body, it is apparently very difficult to recolonize and rebuild the original community.  Even after almost one year, the effects of the cadaver were still noticeable in the composition of the testate amoeba community.

The authors conclude that testate amoebae may actually be good forensic tools to estimate post-mortem intervals.  I’ve heard a bigger experiment exploring distinct types of habitats is in the works.  Perhaps the authors shouldn’t be surprised if they receive a phone call from the producers of CSI or another forensic show where they are looking for some kind of new forensic evidence…

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