Adherent eukaryotic cells typically exhibit amoeboid locomotion through actin polymerization and bleb-driven mechanisms. However, testate amoebae, which enclose their bodies within a shell, exhibit variation in these locomotion types. This study focused on Arcella, a representative testate amoeba that pulls its shell using multiple pseudopods extending from a single aperture on the ventral side. Arcella may be found in peatlands and freshwater, where it adapts its movement to various substrates. We characterized its movement on glass as well as hard, and soft gel substrates through detailed observation. The results indicated a higher randomness in motion on the soft gel, which was influenced by the pseudopodial elongation direction. Additionally, we evaluated the relationship between movement direction and traction stress. The dipole moment of the traction stress field determined the axis of motion, whereas quadrupole moments were correlated with forward and lateral movements. Although some relationships between multipole moments and velocity were shared with other cells, Arcella exhibited unique characteristics in its movement mechanism, which likely occurred due to its use of multiple pseudopods alongside its shell.

Assessing the Value of Testate Amoebae and their Functional Traits in Detecting Climate Change-Induced Peatland Drying

High-latitude ecosystems are undergoing rapid ecological changes in response to climate warming. While some changes are well studied, the responses of microbial communities remain less understood. Testate amoebae, shell-producing protists well preserved in peat, provide a means to reconstruct past microbial dynamics. Mixotrophic taxa such as Archerella flavum host algal endosymbionts (zoochlorellae), allowing both heterotrophic and phototrophic energy acquisition. Previous work has demonstrated that these pathways result in different δ13C values. We applied a novel stable isotope approach to a peat core from the North Slope of Alaska to reconstruct changes in phototrophy by Archerella flavum. δ13C values were measured on Archerella flavum tests (i.e. shells) and Sphagnum, and a two-endmember mixing model was used to estimate relative usage of phototrophy through time. δ13C values were compared with testate amoeba community composition, test size, vegetation, and historical climate. Archerella flavum δ13C values were consistently more positive than Sphagnum δ13C values in the peat core, and patterns indicated greater phototrophy use after the late 1980s CE. This shift was followed by expansion of Archerella flavum populations and a trend of decreasing test length in several testate amoeba taxa. Increased phototrophy was associated with higher peat C:N ratios, indicating more oligotrophic conditions. From 2007 to 2019 CE, the length of the snow-free growing season was correlated with estimates of phototrophy usage, with more phototrophy during longer growing seasons. δ13C analyses of mixotrophic testate amoebae are a powerful tool for reconstructing microbial nutritional strategies and responses to past environmental change.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00248-025-02681-3.

Healthy peatlands are the largest terrestrial carbon (C) store despite covering only approximately 3% of total global land surface. However, peatland health is threatened by anthropogenic exploitation and degradation by drainage. Consequently, large-scale ambitious projects to re-wet and restore peatlands have been initiated. It is hoped that they will sequester C and provide a nature-based solution to climate change. The organic-rich peat soils contained in peatlands play an important role in the global C cycle and other biogeochemical cycles, including global silicon (Si) cycling. Testate amoebae (TA) are a dominant group of microbial consumers in peatlands, and their siliceous shells form protozoic Si pools, which represent an important biological sink for Si in these ecosystems. Seasonal variations and the influence of peatland microtopography on protozoic Si pools are unexplored areas of research. In this study, we present data on protozoic Si pools in a former raised bog under restoration management. Our findings show variability in protozoic Si pools between seasons, microtopography, and vegetation cover. There was a clear trend of higher protozoic Si pools in hummocks than in hollows in all seasons, and higher protozoic Si pools were associated with higher water table depth and lower temperatures in colder/wetter months (November/autumn, February/winter) than that in warmer/drier months (May/spring, August/summer). These results suggest that future quantification of protozoic Si pools in peatlands should consider fine-scale spatiotemporal variables as an important feature in the experimental design.

Maintaining appropriate peatland hydrology, notably through the regulation of the depth to water table (DWT), is crucial for peatland conservation, restoration, and the mitigation of greenhouse gas (GHG) emissions. We assess the long-term ecological impact of hydrological changes, primarily induced by drainage, in ombrotrophic peatlands across Europe. Our analysis is based on novel palaeoecological data from seven peat cores collected from sites that have experienced varying degrees of anthropogenic disturbance. We reconstructed historical DWT fluctuations using plant macrofossil and testate amoeba analyses at high resolution. By applying Threshold Indicator Taxa Analysis (TITAN) models, we identified species-specific and community-level response thresholds to changes in reconstructed water table. This approach revealed two distinct change points: the first, at c. 7 cm DWT, corresponds to hydrological conditions favourable for moisture-dependent Sphagnum species. The second, at c. 22 cm DWT, is associated with more drought-adapted plant taxa and signals ecosystem degradation. The interval between these change points represents a transition zone between optimal and suboptimal conditions for peatland functioning. An additional TITAN analysis, designed to identify the timing of major ecological changes, indicates that peatland degradation has intensified over the past two centuries and accelerated in recent decades. Our findings further reveal that plant and testate amoebae communities often remain distinct from those of undisturbed peatlands, even after hydrological restoration. This underscores the importance of preserving sites that still retain near-natural conditions. Based on our results (and consistent with previous studies) we recommend maintaining the water table close to the surface, i.e., a DWT of approximately 10 cm below the surface as an optimal target for both peatland conservation and restoration. Such conditions not only support ecological integrity but are also associated with reduced GHG emissions and higher peat accumulation rates, reinforcing the role of ombrotrophic peatlands as long-term carbon sinks.

The Western Siberian peatlands rank among the largest in the Northern Hemisphere. This study investigates peatland development and palaeohydrological changes of the Mukhrino mire during the Holocene focussing on climatic, regional and local factors. The multiproxy and multi-core approach reveals spatial variability driven by topography and sedimentary conditions. Our study integrates testate amoebae, plant macrofossils, peat geochemical and biomarkers to provide insights into past vegetation and environmental conditions. Peat accumulation in Mukhrino mire began in the early Holocene, with regional vegetation influenced by climatic and soil factors. Forest cover has been present since the Early Holocene. Birch and pine dominated in the drained areas and episodic regional presence of Tilia and Ulmus indicated warmer intervals. Since ~8800 cal yr BP, Mukhrino mire transitioned to an oligotrophic/ombrotrophic state dominated by Sphagnum fuscum . A key focus of this study is the dynamics of peatland surface wetness over millennia. Proxy-specific responses revealed both short-term variability (via testate amoebae) and long-term climatic trends (via plant macrofossils). Local dry phases (~6500–5700/4700 and 2200–1800 cal yr BP) resulted in partial mire afforestation, while wetter periods (~5700/4700–2500 cal yr BP) facilitated the restoration of its current state. Comparisons with prior studies identified two wet and four dry zones, with synchronised wetness trends across cores despite localised variations in peat accumulation rates. A pronounced local wet phase (~6700–6800 cal yr BP) corresponds with a marker layer from nearby Lake Svetlenkoye sediments (~8000–6700 cal yr BP), attributed to Ob River palaeo-floods. This evidence supports the presence of regionally wet environmental conditions during this period.

Protists play important roles in nutrient cycling across ecosystems, yet the composition and function of their associated microbiomes remain poorly studied. Here, we use cultivation-independent single-cell isolation and genome-resolved metagenomics to investigate the microbiomes and viromes of more than 100 uncultivated ciliates and amoebae from diverse environments. Our findings reveal unique microbiome structures and complex associations with bacterial symbionts and viruses, with stark differences between ciliates and amoebae. We recover 117 microbial genomes affiliated with known eukaryotic endosymbionts, including Holosporales, Rickettsiales, Legionellales, Chlamydiae, and Babelota, and 258 genomes linked to host-associated Patescibacteriota. Many show genome reduction and genes related to toxin-antitoxin systems and nucleotide parasitism, indicating adaptation to intracellular lifestyles. We also identify more than 80 giant viruses from diverse lineages, some actively expressing genes in single-cell transcriptomes, along with other viruses predicted to infect eukaryotes or symbiotic bacteria. The frequent co-occurrence of giant viruses and microbial symbionts, especially in amoebae, suggests multipartite interactions. Together, our study highlights protists as hubs of microbial and viral associations and provides a broad view of the diversity, activity, and ecological importance of their hidden partners.

Abstract. This study investigates the vegetation and hydrological dynamics of Linje peatland in northern Poland during the past ∼11 500 years by integrating testate amoebae and plant macrofossil analyses. The Linje profile is currently the only complete Holocene peat record in Central Europe and offers valuable insights into long-term climate variability and its ecological consequences for peatland ecosystems. The results reveal significant changes in peatland wetness and vegetation driven by autogenic processes, climatic fluctuations and anthropogenic influences. Major bryophyte species turnovers occurred ∼11 200, ∼10 350, ∼8200, 7500, ∼5500, ∼600, and ∼450 cal BP often coinciding with declines in Archerella flavum and Hyalosphenia papilio abundances. Both proxies indicate a marked period of drier conditions between ∼ 7600 and ∼ 6800 cal BP corresponding with the Holocene Thermal Maximum. Additionally, testate amoebae data suggest further disturbances at ∼ 3050, ∼ 2000, and ∼ 200 cal BP, and the latter, linked to a permanent shift in species composition, implies lasting changes to peatland conditions caused by intensified human activity. Around the end of the Early Holocene, most species turnovers and disturbances began to align with Holocene Rapid Climate Change (RCC) events.

Determinants of testate amoeba community dynamics in urban waters: Effects of heatwave, air pollution, and hydrological gradient.

Abstract Observations on the North Slope of Alaska have revealed patches of Sphagnum peat within the widespread matrix of tussock tundra on mineral soils. Little is known about the developmental history of these Sphagnum patches and whether they represent incipient peatlands established in response to warming‐related environmental changes. Nine peat cores were collected from nine Sphagnum ‐dominated peat patches spanning an approximately 300‐km longitudinal gradient on the North Slope to determine their development and establishment history. Stratigraphically constrained cluster analysis was applied to plant macrofossil data, carbon‐to‐nitrogen ratios, and total organic matter measured from bulk peat to delineate developmental phases, and radiocarbon dating was used to constrain the timing of Sphagnum peat patch establishment. We compared these data to changes in testate amoeba community composition and amoeba‐inferred water‐table depth and pH in six of the peat cores. We also compared Sphagnum peat‐patch development and establishment history to paleoclimate and local instrumental temperature records. Results indicated a predictable pattern that describes the transition from moist tussock tundra to Sphagnum peat. Furthermore, although Sphagnum has been present on the North Slope for millennia, our data suggest that Sphagnum ‐dominated peat patches constitute recent landscape features, mainly established in the 1800s and 1900s, and with rapidly increasing Sphagnum abundance in the past 50 years. Sphagnum expansion was associated with pronounced changes in testate amoeba communities, including an increase in mixotrophic taxa and species associated with densely growing Sphagnum, and community changes consistent with drying and increased acidity. The recent development of Sphagnum ‐dominated peat patches has been associated with warming air and soil temperatures, active layer deepening, and earlier snowmelt. Sphagnum expansion has also been observed in other arctic regions, and understanding the extent and growth potential of Sphagnum peat patches has implications for understanding and anticipating changes in carbon cycling, edaphic conditions, permafrost thermal regimes, and floristic diversity.

Testate amoebae as paleoenvironmental indicators in peatlands: calibration-dataset synthesis and assessment of modern analogues using the Neotoma Paleoecology Database

Testate amoeba functional traits and indicator taxa are important tools for tracking peatland restoration effectiveness.

Characterizing lineage-specific genes in testate lobose amoebae (Arcellinida).

Ecoregional patterns of protist communities in mineral and organic soils: assembly processes, functional traits and diversity of testate amoebae in Northern Eurasia

Testate amoebae are protists with protective external shells, unicellular free-living and regarded as good bioindicators of environmental alteration. The occurrence of testate amoebae inhabiting the moss habitats was not recorded in the state of Jharkhand earlier. Therefore, this is the first description of species composition and diversity in the area. In this preliminary study, the samples of moss were taken out on the surface of the soil and the wall in different sites of Argaghat in the Giridih district of Jharkhand. There were 12 different species of testate amoebae found based on analysis which included 6 genera and 6 families. Testate amoebae species are known to be ecologically sensitive and are very useful in monitoring the environment, as they can provide indications on the health and quality of their immediate habitats. In general, the results can substantiate the usefulness of testate amoebae as bioindicators, the study also represented an important source of base data that can be used in future to comprehend the distribution and richness of testate amoebae in India and can demonstrating their importance in monitoring the ecosystem in understudied regions.

Abstract. The frequency of extreme events worldwide is steadily increasing. Therefore, it is crucial to recognize the accompanying response of different ecosystems. Monoculture tree plantations with simplified ecosystem linkages in food webs are particularly vulnerable to catastrophic events like fires, wind throws, droughts, and insect outbreaks. These events threaten forests and other associated ecosystems, including peatlands, which are extremely important in regulating the global carbon cycle and, thus, mitigating the effects of a warming climate. Here, we traced a 2000-year history of the Miały peatland, which is located in one of Poland's largest pine plantation complexes, and we examined how this peatland responded to some of the largest environmental disasters observed in the 20th century across central Europe: the 1922–1924 Panolis flammea outbreak and the 1992 fire. As a disturbance proxy, we used a multi-proxy palaeoecological analysis (plant macrofossils, testate amoebae, pollen, non-pollen palynomorphs, and micro- and macrocharcoal) supported by a neodymium isotope record. We showed several critical transitions in the peatland associated with extreme events and anthropogenic impacts, which triggered significant changes in the peatland's ecological status.

Trait-based predictors of feeding ecology patterns in shelled microorganisms.

Tales of the crown: An integrative approach to the testate amoeba Galeripora dentata (Ehrenberg, 1830) Siemensma, 2021 (Amoebozoa, Arcellinida, Arcellidae).

The paper presents the results of a microfossil study of Holocene sediments in the Yana River flow zone in the southeastern part of the Laptev Sea. A rich diatom flora (242 species and intraspecific taxa, of which 177 species are freshwater) was revealed; additionally, five species of marine tintinnids (planktonic ciliates) and 15 species of freshwater testate amoebae (testacean) were discovered for the first time in the sea sediments. Three assemblages of microfossils reflecting the phases of environmental changes during the Holocene transgression are distinguished in the studied sediments of core LV83-32. Assemblage 1 was formed under terrestrial conditions (assemblage of diatoms Eunotia-Pinnularia and testacean Difflugia-Cylindrifflugia-Centropyxis), assemblage 2 in the zone of mixing of sea and fresh waters (assemblages of diatoms Cyclotella striata-Aulacoseira, Thalassiosira hyperborea-Chaetoceros and T. hyperborea-Aulacoseira, testacean Cyclopyxis kahli, tintinnids Tintinnopsis fimbriata), and assemblage 3 reflects modern conditions in the inner shelf of the Laptev Sea under the strong influence of river runoff (assemblage of diatoms T. hyperborea-Aulacoseira-M. arctica and tintinnids Tintinnopsis ventricosoides). Changes in the natural environment in the coastal part of the Laptev Sea shelf during the Holocene, established by microfossil assemblages, are confirmed by geochemical data.

Climate change can have a direct impact on the decomposition of organic matter, as well as indirect effects on peatland vegetation (including carnivorous plants) and the microbial communities associated with this environment. The activity of microbes varies depending on the type of peatland they inhabit. Because some microorganisms are highly sensitive, they can be used as indicators of climate change. However, there is still little knowledge of how changes in the temperature of the environment can affect the microbiome of carnivorous plants. The study was conducted to test the following hypotheses: (1) The effect of rising water temperature on the qualitative and quantitative structure of the microbiome of carnivorous peatland plants depends on the type of peatland; (2) habitats with a higher trophic status stimulate the development of microbial communities in the water, but are an unfavourable habitat for the development of the microbiome of plant traps. Irrespective of the type of peatland, the species richness of microorganisms was much higher in the water than in the traps. As the temperature increased, there was an increase in the abundance of bacteria, heterotrophic flagellates, and testate amoebae, which was much more pronounced in the peat bog than in the carbonate fen.