Species Of Amoebae Research Articles

Evaluation of different primers of the 18S rRNA gene to profile amoeba communities in environmental samples

Amoeboid protists, an assemblage of organisms belonging to different phylogenetic lineages, have drawn increasing attention due to their crucial ecological roles in various environments and their potential health risks. Currently, 18S rRNA gene sequencing is widely applied for the detection of amoebae. However, it is not clear which is the best primer pair for 18S rRNA gene amplification in amoebae. This study compared the four most commonly used primer pairs for revealing the diversity, composition, core species, and community assembly processes of amoebae in water and sediments. We found that the choice of primers artificially influences the detection of community composition of amoebae. We also found that short-read fragments may lead to mismatches in taxonomy and were not suitable for phylogenetic analyses. In contrast, full-length primers could detect the highest number of amoeba lineages and annotate 80% of reads belonging to amoebae to known species. However, full-length primers did not detect as many amoeba species as V4 primers. Moreover, we showed that beta diversity and community assembly determination were largely unaffected by primer choice, but different primers could influence our interpretations of the ecological process underlying stochasticity and determinism. This study indicates that full-length read sequencing and V4 region Illumina sequencing are suitable for profiling amoeba diversity in the environment.

Recognition of Cell Wall Mannosylated Components as a Conserved Feature for Fungal Entrance, Adaptation and Survival Within Trophozoites of Acanthamoeba castellanii and Murine Macrophages.

Acanthamoeba castellanii (Ac) is a species of free-living amoebae (FLAs) that has been widely applied as a model for the study of host-parasite interactions and characterization of environmental symbionts. The sharing of niches between Ac and potential pathogens, such as fungi, favors associations between these organisms. Through predatory behavior, Ac enhances fungal survival, dissemination, and virulence in their intracellular milieu, training these pathogens and granting subsequent success in events of infections to more evolved hosts. In recent studies, our group characterized the amoeboid mannose binding proteins (MBPs) as one of the main fungal recognition pathways. Similarly, mannose-binding lectins play a key role in activating antifungal responses by immune cells. Even in the face of similarities, the distinct impacts and degrees of affinity of fungal recognition for mannose receptors in amoeboid and animal hosts are poorly understood. In this work, we have identified high-affinity ligands for mannosylated fungal cell wall residues expressed on the surface of amoebas and macrophages and determined the relative importance of these pathways in the antifungal responses comparing both phagocytic models. Mannose-purified surface proteins (MPPs) from both phagocytes showed binding to isolated mannose/mannans and mannosylated fungal cell wall targets. Although macrophage MPPs had more intense binding when compared to the amoeba receptors, the inhibition of this pathway affects fungal internalization and survival in both phagocytes. Mass spectrometry identified several MPPs in both models, and in silico alignment showed highly conserved regions between spotted amoeboid receptors (MBP and MBP1) and immune receptors (Mrc1 and Mrc2) and potential molecular mimicry, pointing to a possible convergent evolution of pathogen recognition mechanisms.

Amoeba & Biofilms in UK Chlorinated Drinking Water Distributions Systems: Impact on Water Safety

Amoeba-related diseases have been related with the presence of certain amoebas in domestic water, including drinking water. Biofilms in drinking water distribution systems are able to support amoeba growth by providing a food source and protecting them against disinfectants. Additionally, amoeba growth can be favoured by warm temperatures and climate change appears to contribute to its geographic spread. The presence of amoeba and its association with potential pathogenic bacteria was studied in a real-scale chlorinated DWDS. The test facility comprised three independent pipe loops fed with water from the local water supply and for this study a varied flow hydraulic profile was applied based on daily patterns observed in real UK distribution networks. The daily regime was repeated for a biofilm growth phase of 30 days. Amoeba viability was tested by a culture-based method, non-nutrient agar (NNA)-E. coli plates, and then confirm by qPCR using specific primers to detect species of amoeba including Naegleria and Acanthamoeba. Amplicon sequencing of the 16s rRNA gene was used to characterise the biofilm and planktonic bacterial communities. Several amoeba species belonging to the genera Acanthamoeba, Vermamoeba and Naegleria were identified in 30-day old biofilm samples. While the bacterial communities in biofilms were dominated by Variovorax, Pseudomonas and Aquabacterium. This study yielded new insights on the dynamics of amoeba and bacterial communities in DWDS. However, more research is required to accurately establish the impact of these inter-kingdom associations on human health.

New finds of naked amoebae in the Black Sea (Ukraine)

Our research identified 12 species of naked amoebae of eight morphotypes in the Black Sea (coastal zone of Zatoka village, Odessa region). In more than half of the samples, Vannella devonica, Vannella aberdonica and Thecamoeba orbis were present. The species Saccamoeba marina, Vexillifera armata, Vannella plurinucleolus, Cochliopodium gulosum, and Stenamoeba sp. were rare and infrequent in our samples. The upper layers of the bottom sediment were inhabited by all 12 species of amoebae; two layers were inhabited by S. marina, V. armata, V. devonica, V. aberdonica, Mayorella gemmifera, T. orbis, Stenamoeba sp., <Acanthamoeba griffin; three layers were colonized by V. armata, V. devonica, V. aberdonica, T. orbis, Stenamoeba sp., and A. griffini. All amoebae species and their morphotypes occurred at Black Sea water temperatures of + 22 ºС to + 26 ºС and salinity of 15.5 ‰ to 17.6 ‰. The species V. simplex and A. griffini, which belong to the fan–shaped and acanthopodial morphotypes, respectively, were collected in samples from the Mediterranean Sea at water temperatures of +29 ºС and salinity of 37.8 ‰. The amoebas identified belong to two classes, seven orders, eight families and eight genera. Dataset published through Zenodo (Doi:10.5281/zenodo.6557376)

Species and morphotypes complexes of naked amoebae in several types of soils of Ukraine

Species and morphotypes complexes of naked amoebae in several types of soils of Ukraine

New finds of naked amoebae

Findings of naked amoebae in various habitats of Ukraine and other territories are presented. Saccamoeba sp., Thecamoeba similis (Greeff, 1891) Lepşi, 1960, Vexillifera bacillipedes Page, 1969, Vannella lata Page, 1988, Acanthamoeba sp., Willaertia magna De Jonckheere, Dive, Pussard & Vickerman, 1984 were identified based on morphological data and molecular genetic research methods. All these species of amoebae are characterized according to our own observations and measurements and the published data. The amoebae we found belong to three classes (Tubulinea, Discosea, Heterolobosea), six orders (Euamoebida, Thecamoebida, Dactylopodida, Vannellida, Centramoebida, Schizopyrenida), six families (Hartmannellidae, Thecamoebidae, Vexilliferidae, Vannellidae, Acanthamoebidae, Vahlkampfiidae) and six genera (Saccamoeba, Thecamoeba, Vexillifera, Vannella, Acanthamoeba, Willaertia). W. magna was the least common in water bodies of different regions of Ukraine; Saccamoeba sp., V. bacillipedes in the studied water bodies are either uncommon species or occupy the middle position in terms of frequency of occurrence In the water bodies of Ukraine T. similis, V. lata, Acanthamoeba sp. are both the least common and the most common species, or occupy the middle position in terms of frequency of occurrence. The following ecological groups of naked amoebae have been identified in relation to temperature: eurythermal, psychrophilic stenothermal, thermophilic stenothermal. In relation to the concentration of dissolved oxygen in water: euryoxidic and stenooxidic. Three species of amoebae can withstand either a wide range of values of organic substances dissolved in water, or belong to stenobiont species. The recorded amoebae belong to monotactic (Saccamoeba sp.), striate (T. similis), dactylopodial (V. bacillipedes), fan-shaped (V. lata), acanthopodial (Acanthamoeba sp.) and eruptive (W. magna) morphotypes.

Certesella larai (Amoebozoa: Arcellinida: Hyalospheniformes) a new soil testate amoeba species from the Dominican Republic and Chile challenges the definition of genera Certesella and Porosia

Microbial diversity is known to be huge but remains only partly documented. Testate amoebae are a relatively well studied group or free-living protists that build morphologically characteristic shells on which the taxonomy of this group is mainly based. Among testate amoebae, the Hyalospheniformes are especially well documented and are a model group for microbial biogeography. Here we describe a new species of genus Certesella from Sphagnum mosses and forest litter samples collected in the Dominican Republic and Chile. We name this species Certesella larai to honour our esteemed colleague Enrique Lara. This species bears two large pores connected by tube, which are characteristic of the genera Porosia and Certesella. The new species fits best in the latter genus given the presence of a distinct, sometimes denticulated, neck with a bulge that is absent in genus Porosia but occurs in Certesella. Its elongated shape (length/breadth ratio 2.03–2.58) only overlaps with C. certesi, which is distinguishable by the presence of a distinct longitudinal groove in the neck region that is absent from the new species. Interestingly most specimens lacked the internal teeth which are usually present in members of genus Certesella. As such, while the morphology of C. larai strongly suggests a belonging to genus Certesella, molecular analyses are still required to confirm its phylogenetic position, clarify the relationships among all species in genera Porosia and Certesella and the definition and validity of these two genera. The presence of this new species in two rather distant regions – Caribbean and central Chile – suggests it is likely widespread, but possibly rare. However, this perception may be due to a sampling bias in favour of Sphagnum mosses and wet and organic-rich habitats. This illustrates the need for a more systematic sampling effort to document the full and mostly unknown taxonomic diversity of soil protists.

Balamuthia spinosa n. sp. (Amoebozoa, Discosea) from the brackish-water sediments of Nivå Bay (Baltic Sea, The Sound)-a novel potential vector of Legionella pneumophila in the environment.

We have found a new free-living amoeba species named Balamuthia spinosa n. sp. (Amoebozoa, Discosea) in the bottom sediments of the brackish-water Nivå Bay (Baltic Sea, The Sound). This species resembles members of the genus Stygamoeba morphologically and was (mis)identified as belonging to this genus during the initial investigation. However, SSU rRNA gene data show that it robustly groups with Balamuthia mandrillaris sequence among Acanthopodida and represents a new species of the genus Balamuthia. Fragments of Legionella pneumophila genome were found among the NGS contigs obtained from B. spinosa n. sp., suggesting that this species may be a vector of Legionella in the environment. We discuss a remarkable morphological and ultrastructural similarity between the genus Balamuthia and the genus Stygamoeba. In addition, our phylogenetic analysis based on the SSU rRNA gene sequences revealed a close relationship between the genera Stygamoeba and Vermistella. It is one more confirmation of the order Stygamoebida, which was formed basing on the morphological evidence. The position of these branches close to Thecamoebida clade is congruent with current phylogenomic data.

The Distribution of Intestinal Amoebae in Wild Long-Tailed Macaques (Macaca fascicularis) in Sabang City, Aceh Province, Indonesia

Amoeba that infects primates can also be found in humans and can be zoonotic. This study aims to identify the distribution of intestinal amoeba in the wild Long-Tailed Macaque (LTM) group located at Cot Murong, Kebun Mangga, and Tugu Zero Kilometer Monument (IZKM) in Sabang City, Aceh Province, Indonesia. A total of 177 stool samples from 59 tails from the three LTM groups were examined microscopically. The results of the examination confirmed seven species of intestinal amoeba, three of which belonged to the genus Entamoeba, namely the Entamoeba histolytica/dispar/moshkovskii complex, Entamoeba coli, Entamoeba pölecki, and four other species from different genera, namely Iodamoeba butschlii, Blastocystis sp., Endolimax nana and Dientamoeba fragilis. The prevalence of intestinal amoeba in wild LTM in Sabang City was 57.6% (102/177). Dientamoeba fragilis was only found in the LTM group of Kebun Mangga. Entamoeba coli dominated the highest prevalence in all LTM groups. The LTM group located around Cot Murong and IZKM had a higher concentration of infection with intestinal amoeba than the Kebun Mangga location. The statistical tests showed a significant difference between the proportions of Iodamoeba butschlii, Endolimax nana and Dientamoeba fragilis, both found in the LTM Cot Murong, Kebun Mangga, or IZKM groups. This study is the first to report amoebic infection prevalence in the wild LTM group in Sabang City, Aceh Province. The pathogenic amoeba that cannot be distinguished microscopically from morphologically identical amoebae needs to be identified molecularly to identify variants and their potential as zoonotic agents.
 HIGHLIGHTS
 
 Intestinal amoeba species found in fecal samples of the wild long-tailed macaques group of Sabang City, Aceh Province, Indonesia, can also be found in human stool samples
 As many as three of the seven identified amoeba species, namely Entamoeba histolytica, Dientamoeba fragilis, and Blastocystis sp. is a pathogen that can cause diarrhea and colitis in humans and non-human primates
 The prevalence of amoeba infection in wild macaques in Sabang City is in the high category and tends to increase the incidence of infection in the macaque group, which has more susceptible individuals, namely infants, children, and females
 
 GRAPHICAL ABSTRACT

Biofilm and Related Amoebas in an UK Chlorinated Drinking Water System

Drinking water distribution systems (DWDS) can host pathogenic amoebae, but the role of biofilms in supporting the occurrence of these organisms needs to be fully explored in the UK systems. The presence of amoebae and associated bacteria in biofilms attached to inner pipe surfaces was studied in an experimental full-scale chlorinated distribution system in the UK. Quantitative polymerase change reaction (qPCR) was used to identify and quantify amoebae, whilst the bacterial communities in the biofilms were characterised by sequencing the 16S rRNA gene. Despite the maintenance of a chlorine residual in the network (free chlorine ≥ 0.24 mg/L), several species of amoebae belonging to the genera Acanthamoeba, Vermamoeba, and Naegleria were identified in 30-day-old biofilm samples; however, no amoebae were detected in the water samples analysed. The dominant bacterial communities present in the biofilm samples were Variovorax, Pseudomonas, and Aquabacterium. These results indicate that the biofilm samples contained potential pathogenic amoebae and bacteria, such as Acanthamoeba and Pseudomonas, respectively, which implies a potential public health risk if the biofilms are mobilised into the bulk water. Several of the amoebae identified in this study are able to support the presence of resistant bacteria that can remain viable within these prokaryotic organisms until they reach people’s taps. The identification of the microorganisms associated with the pathogenic amoeba species in biofilms could be used to improve the surveillance of DWDS in order to protect public health.

Cooccurrence of Five Pathogenic Legionella spp. and Two Free-Living Amoebae Species in a Complete Drinking Water System and Cooling Towers.

Pathogenic Legionella species grow optimally inside free-living amoebae to concentrations that increase risks to those who are exposed. The aim of this study was to screen a complete drinking water system and cooling towers for the occurrence of Acanthamoeba spp. and Naegleria fowleri and their cooccurrence with Legionella pneumophila, Legionella anisa, Legionella micdadei, Legionella bozemanii, and Legionella longbeachae. A total of 42 large-volume water samples, including 12 from the reservoir (water source), 24 from two buildings (influents to the buildings and exposure sites (taps)), and six cooling towers were collected and analyzed using droplet digital PCR (ddPCR). N. fowleri cooccurred with L. micdadei in 76 (32/42) of the water samples. In the building water system, the concentrations of N. fowleri and L. micdadei ranged from 1.5 to 1.6 Log10 gene copies (GC)/100 mL, but the concentrations of species increased in the cooling towers. The data obtained in this study illustrate the ecology of pathogenic Legionella species in taps and cooling towers. Investigating Legionella’s ecology in drinking and industrial waters will hopefully lead to better control of these pathogenic species in drinking water supply systems and cooling towers.

Population and molecular responses to warming in Netzelia tuberspinifera – An endemic and sensitive protist from East Asia

With the effects of global warming becoming ever more obvious, biodiversity conservation is facing severe challenges. Currently, a deeper understanding the mechanisms of the effects of warming on sensitive species has become an important topic in aquatic biodiversity and ecological management. Our study first overcame the “challenge” for a sensitive indicator species (Netzelia tuberspinifera, an endemic testate amoeba species in East Asia) of culturing under laboratory conditions, and then explored its molecular response mechanisms to warming using transcriptomic analysis. Our data indicate that temperature mainly drove the geographical and seasonal variation of N. tuberspinifera populations. Transcriptomic results indicate that when the temperature is <25 °C, rising temperature triggers the biosynthesis of ribosomes; while the temperature is >25 °C, it triggers molecular processes related with cell division, test formation and general biomass increase. However, once the temperature exceeds 40 °C, N. tuberspinifera is unable to survive. Following from these results, the distribution of N. tuberspinifera might expand towards higher altitude or latitude regions under global warming. For the first time, our study showed direct evidence for sensitive protozoa species that presents a very narrow adaptation mechanism to local climate. Our work provides fundamental data for regional biodiversity conservation and scientific reference in subtropical and tropical waterbodies.

The therapeutic potential of novel isobenzofuranones against Naegleria fowleri

The Free-Living Amoeba species, Naegleria fowleri is the causative agent of a lethal encephalitis known as Primary Amoebic Encephalitis (PAM). Moreover, most of the reported cases are often related to swimming and/or diving in aquatic environments. In addition, the current therapeutic options against PAM are not fully effective and hence, there is an urgent need to develop novel therapeutic agents against this disease. Previously isobenzofuranones compounds have been reported to present antiprotozoal and antifungal activity among others. However, to the best of our knowledge, these molecules have not been previously tested against N. fowleri. Therefore, the aim of this study was to evaluate the activity of 14 novel isobenzofuranones against this pathogenic amoeba. The most active and less toxic molecules, were assayed in order to check induction of Programmed Cell Death (PCD) in the treated amoebae. The obtained results showed that these molecules were able to eliminate N. fowleri trophozoites and also induced PCD. Therefore, the tested isobenzofuranones could be potential therapeutic candidates for the treatment of PAM.

Searching for an ecological baseline: Long-term ecology of a post-extraction restored bog in Northern Estonia

The exploitation of peatlands in Estonia, which began in the 17th century, has degraded them to a great extent. Consequently, cutover and drained peatlands have become the sources of CO2. Global warming has led to a need for policies focusing on the protection and restoration of drained and degraded peatlands. Hence, to compare the effect/progress of restoration with the past pristine ecosystem baseline before the peatland was destroyed by cutting, we examined a peat core from North Estonia using chronology based on 14C by analyzing several proxies in high resolution including testate amoebae, plant macrofossils, pollen, non-pollen palynomorphs, and diatoms. The results revealed a striking ecological contrast between the pristine (ca. 2 kyrs) and restored state (currently) of the peatland. The pristine state was characterized by a domination of Sphagnum fuscum/rubellum and Archerella flavum, suggesting that extraction area of Hara peatland was a wet and stable ombrotrophic bog. As a result of peat exploitation, deposits comprising the last ca. 2 kyrs were cut. In turn an important feature of the restored section of the peat core was the domination of a green algae (Chlorophyta) and Eriophorum vaginatum as well as testate amoebae species Arcella discoides, which is considered an indicator of hydrological instability. The main difference between the predisturbed and restored parts of the peat core section was that a minor cover of peat-forming Sphagnum and mixotrophic testate amoebae was present in the top inundated part. We state that a healthy raised bog—the target of restoration—should consist abundant mixotrophic testate amoebae such as Archerella flavum and Hyalosphenia papilio which are good indicators of a well-functioning Sphagnum bog ecosystem even if the Sphagnum species differ from the reconstructed ecological baseline conditions. Our study highlights the extensive damage caused to the peat-forming ombrotrophic peatland by extraction and how difficult, challenging, and time-consuming is the process of ecological restoration.

Ecology of peatland testate amoebae in Svalbard and the development of transfer functions for reconstructing past water-table depth and pH

Peatlands are valuable archives of information about past environmental conditions and represent a globally-important carbon store. Robust proxy methods are required to reconstruct past ecohydrological dynamics in high-latitude peatlands to improve our understanding of change in these carbon-rich ecosystems. The High Arctic peatlands in Svalbard are at the northern limit of current peatland distribution and have experienced rapidly rising temperatures of 0.81 °C per decade since 1958. We examine the ecology of peatland testate amoebae in surface vegetation samples from permafrost peatlands on Spitsbergen, the largest island of the Svalbard archipelago, and develop new transfer functions to reconstruct water-table depth (WTD) and pH that can be applied to understand past peatland ecosystem dynamics in response to climate change. These transfer functions are the first of their kind for peatlands in Svalbard and the northernmost developed to date. Multivariate statistical analysis shows that WTD and pore water pH are the dominant controls on testate amoeba species distribution. This finding is consistent with results from peatlands in lower latitudes with regard to WTD and supports work showing that when samples are taken across a long enough trophic gradient, peatland trophic status is an important control on the distribution of testate amoebae. No differences were found between transfer functions including and excluding the taxa with weak idiosomic tests (WISTs) that are most susceptible to decay. The final models for application to fossil samples therefore excluded these taxa. The WTD transfer function demonstrates the best performance (R2LOO = 0.719, RMSEPLOO = 3.2 cm), but the pH transfer function also performs well (R2LOO = 0.690, RMSEPLOO = 0.320). The transfer functions were applied to a core from western Spitsbergen and suggest drying conditions ~1750 CE, followed by a trend of recent wetting and increasing pH from ~1920 CE. These new transfer functions allow the reconstruction of past peatland WTD and pH in Svalbard, thereby enabling a greater understanding of long-term ecohydrological dynamics in these rapidly changing ecosystems.

South American Entamoeba dispar strains produce amoebic liver abscesses with different pathogenicities and evolutionary kinetics

Amoebiasis is a protozoan disease caused by Entamoeba histolytica, and presents a geographic distribution of worldwide amplitude, high incidence, sometimes accompanied by severe clinical manifestations such as amoebic colitis and Amoebic Liver Abscess (ALA), remaining as a public health problem in developing countries. Entamoeba dispar is another species of amoeba that infects approximately 12% of the world's population, and it has previously been classified as noninvasive. However, E. dispar has already been isolated from patients with symptomatic non-dysenteric colitis, as well as its DNA sequences were detected and genotyped in samples from patients with dysenteric colitis, and patients with ALA, suggesting that this species could also be involved in the development of lesions in the large intestine and liver of human beings. In this context, this study aims to evaluate the ability of isolated strains of Entamoeba dispar in South America to cause liver damage, and to better characterize histopathological findings in 3, 8, 12 and 16 days after infection (DAI). Firstly, we assessed whether trophozoites from MCR, ACFN, ICS, ADO and VEJ E. dispar strains, and EGG Entamoeba histolytica strain differed in their in vitro phagocytosis ability, being related to greater ability to phagocyte with greater virulence. Then, we investigate and characterize histopathological changes present in the liver of mice induced by different strains of E. dispar. Our results demonstrated that trophozoites from E. dispar strains are capable of phagocyting human erythrocytes, but in lower amounts than Entamoeba histolytica. In addition, we described and characterized the lesions in different periods after infection by different E. dispar strains, and identified ACFN as the most pathogenic strain, followed by MCR. The large areas of necrosis produced by the ACFN strain as the eighth DAI, which also show high parasitism, led to 100% mortality. On the other hand, the ICS, ADO and VEJ strains did not produce mortality, and this was correlated with the presence of well-developed chronic granulomatous inflammation, necrosis absorption throughout the infection, and regeneration of the liver parenchyma. The greater pathogenicity of the ACFN strain strongly suggests that this strain could be producing higher levels of virulence factors. As the experimental infection, the heterogeneity of biological behavior of different Entamoeba dispar strains could be involved in the development of undiagnosed human clinical conditions.

Transport and Retention of Free-Living Amoeba Spores in Porous Media: Effects of Operational Parameters and Extracellular Polymeric Substances.

Amoebas are protists that are widespread in water and soil environments. Some species are pathogenic, inducing potentially lethal effects on humans, making them a major threat to public health. Nonpathogenic amoebas are also of concern because they have the potential to carry a mini-microbiome of bacteria, either transiently or via more long-term stable transport. Due to their resistance to disinfection processes, the physical removal of amoeba by filtration is necessary to prevent their propagation throughout drinking water distribution networks and occurrence in tap water. In this study, a model amoeba species Dictyostelium discoideum was used to study the transport and retention behavior of amoeba spores in porous media. The key factors affecting the transport behavior of amoeba spores in fully saturated media were comprehensively evaluated, with experiments performed using a quartz crystal microbalance with dissipation monitoring (QCM-D) and parallel plate chamber system. The effects of ionic strength (IS) on the deposition of spores were found to be in contrast to the predicted Derjaguin-Landau-Verwey-Overbeek (DLVO) theory that more deposition is observed under lower-IS conditions. The presence of extracellular polymeric substances (EPS) was found to be the main contributor to deposition behavior. Overall, these results provide plausible evidence for the presence of amoeba in tap water. Furthermore, this is one of the first studies to examine the mechanisms affecting the fate of amoeba spores in porous media, providing a significant baseline for future research to minimize the safety risk presented by amoeba in drinking water systems.

A dormant amoeba species can selectively sense and predate on different soil bacteria

Abstract Soil protists are the invisible majority of soil eukaryotes, which are essential but often forgotten parts of the soil ecosystem. They play key roles in microbial food webs by predating on other soil microbes. However, it is not clear how dormant soil protists sense, recognize and feed on diverse microbial prey. In this study, we used a soil amoeba, Dictyostelium discoideum, to study selective discrimination and predation of 14 different bacteria. We found that discrimination and sensing of prey in D. discoideum started as early as resting spores. Dictyostelium discoideum had higher hatching rates, formed bigger amoeba plaques and preferred high nutritional value bacteria. The feeding speed of amoeba on various bacteria was constant and was not linked with sensing of prey or bacterial nutritional value. We also found that higher bacterial density decreased predation efficiency, and one species, P. fluorescens, induced a strong density‐dependent inhibition of amoeba spore production. In conclusion, we find that dormant D. discoideum can selectively sense and predate on different soil bacteria, a process that is likely mediated through active amoeba preference as well as bacterial inhibition. This study provides new insights into the role of protists in shaping soil bacterial communities, and future study needs to assess this in natural soil environments.

Decade-scale change in testate amoebae community primarily driven by anthropogenic disturbance than natural change in a large subtropical reservoir

Understanding the extent of human activities leading to an influx of chemical pollutants that cause substantial environmental transformations is the focus of much ongoing research. In this study, we present a multi-proxy record based on a sediment core from a large subtropical reservoir (Xinfengjiang Reservoir) in south China with an emphasis on the changes in testate amoebae community, in combination with sedimentological (radioactivity, physicochemistry, nutrient and organochlorine pesticides) and climatological (air temperature and precipitation) data over the last three decades. Twenty-seven testate amoebae species belonging to seven genera (Arcella, Centropyxis, Cyclopyxis, Difflugia, Netzelia, Euglypha and Pseudodifflugia) were observed. Species richness, abundance and biomass of testate amoebae were in ranges of 18–26 species, 616–825 ind. ml−1 and 9.0–19.4 μg C ml−1, respectively. Two development stages of the reservoir, dated to 1978–1993 (stage 1) and 1993–2006 (stage 2), were distinguished based on testate amoebae communities. Stage 1 was characterized by elevated dry bulk density, carbon-to‑nitrogen ratio and p,p’-DDE in the sediment core and an impact of nitrogen and sulfur deficiency on testate amoebae. Stage 2 was marked by a decrease of dry bulk density, elevated concentrations of aluminum, iron and carbon, low carbon-to‑nitrogen ratio and organochlorine pesticides, fluctuations in rainfall on shorter and yearly timescales, and a stronger influence of the organochlorine pesticides on testate amoebae. Testate amoebae community change and the identified two-stage development were consistent with atmospheric deposition of organochlorine pesticides from anthropogenic sources inside and outside the reservoir watershed, nutrient influx and sediment physicochemistry. The testate amoebae community dynamics and a strong community-environment relationship in stage 2 were linked with non-random patterns in the biotic neighborhoods of species (deterministic processes). The results suggest a stronger impact of anthropogenic disturbance than natural environmental change on testate amoebae community variation of Xinfengjiang Reservoir over time.

The ecology of testate amoebae and Cladocera in Hawaiian montane peatlands and development of a hydrological transfer function

Peatland complexes in the humid highlands of Hawai‘i are vital refuges of biodiversity and freshwater resources. Hawaiian peat deposits are also rare repositories of terrestrial ecosystem archives located in an otherwise vast expanse of ocean. We investigated the potential for researching the paleohydrological history of Hawaiian montane peatlands on Kohala, Hawai‘i Island through analyses of testate amoebae and Cladocera. Surface peat was collected from a variety of ecohydrological habitats (from water pools to hummocks) and analyzed for modern testate amoeba and cladoceran species relative abundance. We identified 54 morphotype taxa from 21 genera of testate amoebae, 4 taxa and genera of littoral Cladocera, and the common peat rotifer Habrotrocha angusticollis. Testate amoeba diversity and morphotype occurrence mirrored observations from many high-latitude peatland studies. Constrained and unconstrained ordinations support the hypothesis that surface moisture, measured as water-table depth, is an important control on the distribution of testate amoebae and Cladocera in Hawaiian peatlands. Transfer functions relying on weighted-averaging and modern analogs were developed to predict water-table depths from species relative abundance data, and these perform well under leave-one-site-out cross-validation: RMSEP = 9.75–10.3 cm, R2 = 0.56–0.62. Including cladoceran abundance data in the calibration dataset produced modest model improvement: RMSEP = 1–8% and R2 = 2–13%. A weighted-average partial-least-squares transfer function was applied to microfossil assemblages from a 0.5 m-long peat core with a 210Pb decay chronology anchored by ten existing measurements of 210Pb activity and a Bayesian statistical framework. Microfossils were well-preserved in the peat core. The water-table depth optima of an abundant down-core taxa, Hyalosphenia subflava, is not precisely constrained in the calibration data set, but estimates match those of other tropical studies. A reconstruction of water-table depth indicates dry early nineteenth-century conditions, wet conditions in the late 19th to early twentieth centuries, followed by progressive drying for much of the twentieth-century. Testate amoeba composition appears to have been sensitive to severe drought in recent decades. The results signal that assemblages of testate amoebae and Cladocera are useful proxies of Hawaiian peatland paleohydrology and should be considered alongside other archives of Hawaiian environmental history.