Species Of Amoebae Research Articles

Functional traits data for testate amoebae of Northern Holarctic realm

The functional traits of soil protists have been employed in ecological research to enhance comprehension of the underlying mechanisms of ecological processes. Among the numerous soil protists, testate amoebae emerge as a prominent and abundant group, playing a pivotal role in soil micro-food webs. Furthermore, they are regarded as valuable bioindicators for environmental monitoring and palaeoecological studies due to their sensitivity to environmental changes. We screened 372 testate amoebae species widely distributed across Northern Holarctic realm and collected trait data, representing the morphological and feeding characteristics of testate amoebae. The dataset would provide valuable basis for investigation of the functional diversity and ecological roles of testate amoebae, thus facilitating further research on soil protist communities and ecosystem dynamics.

Diversity and Environmental Significance of Moss-Dwelling Testate Amoebae in Various Biotopes Around Nainital Lake, Uttarakhand

The present research aims to record the diversity of testate amoebae occurring in different biotopes around Nainital Lake, Uttarakhand, concerning distribution. Free-living, testate amoebae are single-celled protists with external shells and acting excellent bio-indicators of environmental changes. Collection of Tree, Rock and wall Moss samples was done at different locations around the Nainital Lake area from both the littoral zones and the terrestrial regions. The results show an impressive number of species of testate amoebae; 39 species of testate amoebae span over 11 genera and 8 families that all are new for the region and stress the role of some species in biomonitoring and evaluation of the condition of the environment in these peculiar biotopes. This study not only increases researcher’s knowledge on the testate amoebae species distribution in Nainital Lake but also contributes to the body of knowledge that would be useful for the ecological and environmental status of the area in the future. The outcomes of the research confirm the need for the conservation of the habitats in the area surrounding Nainital Lake to sustain the biodiversity and ecosystems of the region.

Iris setosa Pall. ex Link Extract Reveals Amoebicidal Activity against Acanthamoeba castellanii and Acanthamoeba polyphaga with Low Toxicity to Human Corneal Cells.

Acanthamoeba keratitis (AK) is a sight-threatening and difficult-to-treat ocular infection. The significant side effects of current AK treatments highlight the urgent need to develop a safe and effective AK medication. In this study, the amoebicidal activity of Iris setosa Pall. ex Link extract (ISE) against Acanthamoeba was examined and its specific amoebicidal mechanism was explored. ISE induced significant morphological changes in Acanthamoeba trophozoites and exhibited amoebicidal activity against A. castellanii and A. polyphaga. ISE was further fractionated into five subfractions by sequential extraction with n-hexane, chloroform, ethyl acetate, n-butanol, and water, and their amoebicidal activities and underlying amoebicidal mechanisms were investigated. The n-butanol subfraction of ISE (ISE-BuOH) displayed selective amoebicidal activity against the Acanthamoeba species with minimal cytotoxicity in human corneal cells (HCE-2). ISE-BuOH triggered apoptosis-like programmed cell death (PCD) in amoebae, characterized by DNA fragmentation, increased ROS production, and caspase-3 activity elevation. ISE-BuOH also demonstrated a partial cysticidal effect against the amoeba species. ISE-BuOH could be a promising candidate in the development of therapeutic drugs for AK.

Novel insights on microbiome dynamics during a gill disease outbreak in farmed rainbow trout (Oncorhynchus mykiss)

The generic term “Gill disease” refers to a wide range of disorders that affect the gills and severely impact salmonid aquaculture systems worldwide. In rainbow trout freshwater aquaculture, various etiological agents causing gill diseases have been described, particularly Flavobacterium and Amoeba species, but research studies suggest a more complex and multifactorial aetiology. Here, a cohort of rainbow trout affected by gill disease is monitored both through standard laboratory techniques and 16S rRNA Next-Generation Sequencing (NGS) analysis during a natural disease outbreak and subsequent antibiotic treatment with Oxytetracycline. NGS results show a clear clustering of the samples between pre- and post-treatment based on the microbial community of the gills. Interestingly, the three main pathogenic bacteria species in rainbow trout (Yersinia ruckeri, Flavobacterium psychrophilum, and Flavobacterium branchiophilum) appear to be weak descriptors of the diversity between pre-treatment and post-treatment groups. In this study, the dynamics of the gill microbiome during the outbreak and subsequent treatment are far more complex than previously reported in the literature, and environmental factors seem of the utmost importance in determining gill disease. These findings present a potential novel perspective on the diagnosis and management of gill diseases, showing the limitations of conventional laboratory methodologies in elucidating the complexity of this disease in rainbow trout. To the authors’ knowledge, this work is the first to describe the microbiome of rainbow trout gills during a natural outbreak and subsequent antibiotic treatment. The results of this study suggest that NGS can play a critical role in the analysis and comprehension of gill pathology. Using NGS in future research is highly recommended to gain deeper insights into such diseases correlating gill’s microbiome with other possible cofactors and establish strong prevention guidelines.

Presence and diversity of free-living amoebae and their potential application as water quality indicators.

Free-living amoebae (FLA) are found in diverse environments, such as soils, rivers, and seas. Hence, they can be used as bioindicators to assess the water quality based solely on their presence. In this study, we determined the presence of FLA in river water by filtering water samples collected from various sites and culturing the resulting filtrates. FLA were detected in all the water samples with varying quality grades (Grades Ι-V). The significant increase in the size of the amoebae population with the deterioration in the water quality. Monoxenic cultures of the amoebae were performed, and genomic DNAs were isolated, among which 18S rDNAs were sequenced to identify the amoeba species. Of the 12 species identified, 10 belonged to the Acanthamoeba genus; of the remaining 2 species, one was identified as Vannella croatica and the other as a species of Vermamoeba. Acanthamoeba was detected in samples with Grades Ι to VI quality, whereas the Vermamoeba species was present only in Grade Ι water. V. croatica was found exclusively in water with Grade ΙΙ quality. Following morphological observations, genomic DNA was sequenced using 16S rDNA to determine whether the species of Acanthamoeba harbored endosymbionts. Most of the isolated Acanthamoeba contained endosymbionts, among which 4 species of endogenous bacteria were identified and examined using transmission electron microscopy. This study provides evidence that the distribution of amoebae other than Acanthamoeba may be associated with water quality. However, further confirmation will be required based on accurate water quality ratings and assessments using a more diverse range of FLA.

Enteropathogenic Escherichia coli modulates the virulence and pathogenicity of Entamoeba dispar

Amoebiasis is a disease caused by Entamoeba histolytica, affecting the large intestine of humans and occasionally leading to extra-intestinal lesions. Entamoeba dispar is another amoeba species considered commensal, although it has been identified in patients presenting with dysenteric and nondysenteric colitis, as well as amoebic liver abscess. Amoebic virulence factors are essential for the invasion and development of lesions. There is evidence showing that the association of enterobacteria with trophozoites contributes to increased gene expression of amoebic virulence factors. Enteropathogenic Escherichia coli is an important bacterium causing diarrhea, with high incidence rates in the world population, allowing it to interact with Entamoeba sp. in the same host. In this context, this study aims to evaluate the influence of enteropathogenic Escherichia coli on ACFN and ADO Entamoeba dispar strains by quantifying the gene expression of virulence factors, including galactose/N-acetyl-D-galactosamine-binding lectin, cysteine proteinase 2, and amoebapores A and C. Additionally, the study assesses the progression and morphological aspect of amoebic liver abscess and the profile of inflammatory cells. Our results demonstrated that the interaction between EPEC and ACFN Entamoeba dispar strains was able to increase the gene expression of virulence factors, as well as the lesion area and the activity of the inflammatory infiltrate. However, the association with the ADO strain did not influence the gene expression of virulence factors. Together, our findings indicate that the interaction between EPEC, ACFN, and ADO Entamoeba dispar strains resulted in differences in vitro and in vivo gene expression of Gal/GalNAc-binding lectin and CP2, in enzymatic activities of MPO, NAG, and EPO, and consequently, in the ability to cause lesions.

Identification of new amoebae strains in rainbow trout (Oncorhynchus mykiss, Walbaum) farms affected by nodular gill disease (NGD) in Northeastern Italy.

Nodular gill disease (NGD) is an emerging condition associated with amoeba trophozoites in freshwater salmonid farms. However, unambiguous identification of the pathogens still must be achieved. This study aimed to identify the amoeba species involved in periodic NGD outbreaks in two rainbow trout (Oncorhynchus mykiss) farms in Northeastern Italy. During four episodes (February-April 2023), 88 fish were euthanized, and their gills were evaluated by macroscopic, microscopic and histopathological examination. The macroscopic and microscopic severity of the lesions and the degree of amoebae infestation were scored and statistically evaluated. One gill arch from each animal was put on non-nutrient agar (NNA) Petri dishes for amoeba isolation, cultivation and subsequent identification with SSU rDNA sequencing. Histopathology confirmed moderate to severe lesions consistent with NGD and mild to moderate amoeba infestation. The presence of amoebae was significantly correlated with lesion severity. Light microscopy of cultured amoebae strains and SSU rDNA analysis revealed the presence of a previously characterized amoeba Naegleria sp. strain GERK and several new strains: two strains from Hartmannelidae, three vannelid amoebae from the genus Ripella and cercozoan amoeba Rosculus. Despite the uncertainty in NGD etiopathogenesis and amoebae pathogenic role, identifying known and new amoebae leans towards a possible multi-aetiological origin.

Grazing preferences of three species of amoebae on cyanobacteria and green algae.

Twenty species/isolates of cyanobacteria and green algae were isolated from cyanobacterial bloom samples in lakes associated with the upper Qu'Appelle River drainage system in southern Saskatchewan, Canada. Three amoebae species (Cochliopodium sp., Vannella sp. and Vermamoeba vermiformis) were also isolated from one of these samples, and were subjected to grazing assays to determine which species of cyanobacteria or algae could potentially serve as a food source. Amoeba grazing rates were quantified based on the diameter of the plaque after 12 days on agar plate assays, and by estimation of the amoeba population growth rate from the rate of increase of plaque area. The common cyanobacterial bloom-formers Dolichospermum sp. and Aphanizomenon flos-aquae supported high growth rates for all three amoebae, while green algae, with the exception of one green alga/amoeba combination, did not support growth of the tested amoebae. Many of the cyanobacterial and algal isolates that did not support amoebae growth were ingested, suggesting that ingestion did not determine grazing success. Overall, while the cyanobacteria Dolichospermum sp. and Aphanizomenon flos-aquae were suitable food sources for the amoebae, the other cyanobacteria were grazed in an unpredictable manner, with some species/strains grazed by some amoebae and some species not grazed at all.

Characterization of Rosculus vilicus sp. nov., a rhizarian amoeba interacting with Mycobacterium avium subsp. paratuberculosis.

Free-living amoebae are described as potential reservoirs for pathogenic bacteria in the environment. It has been hypothesized that this might be the case for Mycobacterium avium subsp. paratuberculosis, the bacterium responsible for paratuberculosis. In a previous work, we isolated an amoeba from a water sample in the environment of infected cattle and showed that this amoeba was associated with Mycobacterium avium subsp. paratuberculosis. While a partial 18S rRNA gene has allowed us to suggest that this amoeba was Rosculus-like, at that time we were not able to sub-cultivate it. In the present study, we succeeded in cultivating this strain at 20-25°C. This amoeba is among the smallest (5-7 μm) described. The sequencing of the whole genome allowed us to extract the full 18S rRNA gene and propose this strain as a new species of the Rosculus genus, i.e., R. vilicus. Of note, the mitochondrial genome is particularly large (184,954 bp). Finally, we showed that this amoeba was able to phagocyte Mycobacterium avium subsp. paratuberculosis and that the bacterium was still observed within amoebae after at least 3 days. In conclusion, we characterized a new environmental amoeba species at the cellular and genome level that was able to interact with Mycobacterium avium subsp. paratuberculosis. As a result, R. vilicus is a potential candidate as environmental reservoir for Mycobacterium avium subsp. paratuberculosis but further experiments are needed to test this hypothesis.

Antiamoebic activities of flavonoids against pathogenic free-living amoebae, Naegleria fowleri and Acanthamoeba species.

Free-living amoebae (FLA) rarely cause human infections but can invoke fatal infections in the central nervous system (CNS). No consensus treatment has been established for FLA infections of the CNS, emphasizing the urgent need to discover or develop safe and effective drugs. Flavonoids, natural compounds from plants and plant-derived products, are known to have antiprotozoan activities against several pathogenic protozoa parasites. The anti-FLA activity of flavonoids has also been proposed, while their antiamoebic activity for FLA needs to be emperically determined. We herein evaluated the antiamoebic activities of 18 flavonoids against Naegleria fowleri and Acanthamoeba species which included A. castellanii and A. polyphaga. These flavonoids showed different profiles of antiamoebic activity against N. fowleri and Acanthamoeba species. Demethoxycurcumin, kaempferol, resveratrol, and silybin (A+B) showed in vitro antiamoebic activity against both N. fowleri and Acanthamoeba species. Apigenin, costunolide, (‒)-epicatechin, (‒)-epigallocatechin, rosmarinic acid, and (‒)-trans-caryophyllene showed selective antiamoebic activity for Acanthamoeba species. Luteolin was more effective for N. fowleri. However, afzelin, berberine, (±)-catechin, chelerythrine, genistein, (+)-pinostrobin, and quercetin did not exhibit antiamoebic activity against the amoeba species. They neither showed selective antiamoebic activity with significant cytotoxicity to C6 glial cells. Our results provide a basis for the anti-FLA activity of flavonoids, which can be applied to develope alternative or supplemental therapeutic agents for FLA infections of the CNS.

Prevalence of Legionella in a Public Building Water Plumbing System During COVID-19 Lockdown.

Although water stagnation is widely accepted as an essential factor supporting Legionella growth in plumbing systems and "water flashing" has become a common action for water quality control, additional monitoring data in practical spaces are still needed to back up this recommendation. The lockdown of public buildings during the COVID-19 pandemic provided an ideal time window to collect such data on a large scale. This study investigated how the long-term lockdown of a public building and the subsequent water stagnation impact water quality and the population of Legionella in water. From June 2020 to May 2021, 192 water samples were collected from a public building during the lockdown and reopening due to the COVID-19 pandemic. Each water sample was assessed for common physicochemical characteristics. Concentrations of Legionella and three species of free-living amoeba (FLA) (Acanthamoeba spp., Naegleria fowleri, and Hartmannella vermiformis) were monitored by qPCR. The data suggest that long-term stagnation promotes the population of Legionella spp., Acanthamoeba spp., and N. fowleri. Notable associations were observed between Legionella and FLA. These relationships were impacted by stagnation. These results provide important evidence that can inform future water quality management actions to minimize the risk of Legionella outbreaks by avoiding the occurrence of water stagnation.

Description of a New Species of the Genus Quadrulella (Cockerell, 1909) Kosakyan et al., 2016 (Amoebozoa : Arcellinida) from Western Himalaya, Uttarakhand, India

A new species of testate amoeba namely Quadrulella talukensis Bindu sp.nov. from Western Himalaya, Uttarakhand, Himachal Pradesh, which is closely related to Quadrulella alata Gauthier-Lievre, 1957 is described and illustrated.

Novel cercozoan and heterolobosean protists from the rhizosphere and phyllosphere of two endemic cacti from the Atacama Desert

Cercozoans and heterolobose amoebae are found across terrestrial habitats where they feed on other unicellular microbes, including bacteria, fungi and microalgae. They constitute a significant fraction of soil ecosystems and are integral members of plant microbiota. Here, we present the results on the isolation of protozoans from the rhizosphere and phyllosphere of Browningia candelaris (Meyen) in the Andean Altiplano and Eulychnia taltalensis (F. Ritter) from the Coastal Cordillera of the Atacama Desert, both endemic to this ancient desert. We identified a new heterolobose amoeba species of the genus Allovahlkampfia isolated from cactus soil, three new species of the different glissomonad genera Allapsa, Neoheteromita, Neocercomonas and one new thecofilosean amoeba of the genus Rhogostoma isolated from the phyllosphere of one studied cactus. In addition, one bacterivorous flagellate was isolated from cactus spines and identified as a member of the non-scaled imbricatean family Spongomonadidae (Spongomonas). The isolation of protists from cactus spines extends the knowledge on the habitat ranges of taxa typically found on plant leaves or soils. The molecular data presented here is a prerequisite for further investigations on the ecology and diversity of protists including next-generation sequencing of microhabitats in plants and the rhizosphere, allowing for deeper taxonomic classification.

Acanthamoeba castellanii trophozoites escape killing by neutrophil extracellular traps using their 3′-nucleotidase/nuclease activity

Acanthamoeba castellanii is a free-living amoeba that acts as an opportunistic pathogen for humans and is the pathogenic agent of Acanthamoeba keratitis (AK). A. castellanii may present as proliferative and infective trophozoites or as resistant cysts during their life cycle. The immune response against AK is still poorly explored; however, it is well established that macrophages and neutrophils play essential roles in controlling corneal infection during the disease outcome. The release of NETs is one of the innate immune strategies to prevent parasite infection, especially when neutrophils interact with microorganisms that are too large to be phagocytosed, which is the case for amoeba species. The present work demonstrated that A. castellanii trophozoites can trigger NET formation upon in vitro interaction with neutrophils. Using DNase as a control, we observed increased parasite survival after coinciding with neutrophils, which may be correlated with NET degradation. Indeed, A. castellanii trophozoites degrade the NET DNA scaffold. Molecular analysis confirmed the occurrence of a 3′-nucleotidase/nuclease (3′-NT/NU) in the A. castellanii genome. We also demonstrated that trophozoites exhibit significantly higher 3′-NT/NU activity than cysts, which cannot trigger NET release. Considering that previous studies indicated the pathological role of 3′-NT-/NU in parasite infection, we suggest that this enzyme may act as the mechanism of escape of A. castellanii trophozoites from NETs.

Isolation and genotyping of Acanthamoeba species and Vahlkampfiidae in the harsh environmental conditions in the centre of Iran.

Different species of free-living amoeba (FLA) have been abundantly isolated in harsh environmental conditions such as hot springs and brackish water. The present study aimed to isolate, genotype, and evaluate the pathogenicity of FLAs in Qom Roud, a large river, in the centre of Iran. About 500 mL of water samples (n = 30) were collected from each sampling site and were investigated for the presence of FLAs using morphological and molecular characters. Genotype identification was performed using DNA sequencing and a phylogenetic tree was constructed with the MEGA X software. The pathogenic potential of all positive isolates was evaluated using the tolerance ability test. Morphological and molecular analysis indicated that 14 (46.66%) and two (6.66%) water samples were positive for Acanthamoeba species and Vahlkampfiidae, respectively. According to sequence analysis, Acanthamoeba isolates related to the T4 genotype and Vahlkampfiidae sequences were similar to Naegleria philippinensis. In the next step, thermo- and osmotolerance tests indicated four Acanthamoeba strains are extremely pathogenic. Our data showed the presence of potentially pathogenic Acanthamoeba T4 genotype and N. philippinensis in the super harsh Qom Roud. Contamination of water with virulent T4 genotype of Acanthamoeba may pose risk factors for contact lens users, children, and immunocompromised people.

New Records of Testate Amoebae in Shenthuriney Wildlife Sanctuary, Kerala, India: Insights into Microbial Biodiversity

This report summarizes the results hitherto achieved in the study of moss inhabitant testate amoebae in Shenthuriney WLS, part of Western Ghats, Kerala. This is the first study on this important protozoan group in the sanctuary to document the testate fauna.The study reveals the novel records of 28 species of testate amoebae span over 6 families and 9 genera from Shenthuriney WLS, Kerala.

Uncovering microbial food webs using machine learning

Microbial trophic interactions are an important aspect of microbiomes in any ecosystem. They can reveal how microbial diversity modulates ecosystem functioning. However, uncovering microbial feeding interactions is a challenge because direct observation of predation is difficult with classical approaches such as behaviour and gut contents analyses. To overcome this issue, recent developments in trait-matching and machine-learning approaches are promising for successfully inferring microbial feeding links. Here, we tested the ability of six machine-learning algorithms for predicting microbial feeding links, based on species traits and taxonomy. By incorporating organism speed, size and abundance into the model predictions, we further estimated the probability of feeding links occurring. We found that the model trained with the boosted regression trees algorithm predicted feeding links between microbes best. Sensitivity analyses showed that feeding link predictions were robust against faulty predictors in the training set, and capable of predicting feeding links for empirical datasets containing up to 50% of new taxa. We cross-validated the feeding link predictions using an empirical dataset from a Sphagnum-dominated peatland with direct feeding observations for two dominant testate amoeba predators. The feeding habits of the two testate amoeba species were comparable between microscopic observations and model predictions. Machine learning thus offers a means to develop robust models for studying microbial food webs. It offers a route to combine traditional observations with DNA-based sampling strategies to upscale soil biodiversity research along ecological gradients.

Expansion of the cytochrome C oxidase subunit I database and description of four new lobose testate amoebae species (Amoebozoa; Arcellinida)

Arcellinida is ascending in importance in protistology, but description of their diversity still presents multiple challenges. Furthermore, applicable tools for surveillance of these organisms are still in developing stages. Importantly, a good database that sets a correspondence between molecular barcodes and species morphology is lacking. Cytochrome oxidase (COI) has been suggested as the most relevant marker for species discrimination in Arcellinida. However, some major groups of Arcellinida are still lacking a COI sequence. Here we expand the database of COI marker sequences for Arcellinids, using single-cell PCR, transcriptomics, and database scavenging. In the present work, we added 24 new Arcellinida COI sequences to the database, covering all unsampled infra- and suborders. Additionally, we added six new SSUrRNA sequences and described four new species using morphological, morphometrical, and molecular evidence: Heleopera steppica, Centropyxis blatta, Arcella uspiensis, and Cylindrifflugia periurbana. This new database will provide a new starting point to address new research questions from shell evolution, biogeography, and systematics of arcellinids.

History of vegetation and fires in the Arctic part of the Pur-Taz interfluve in the Holocene

The global climate change and significantly increased anthropogenic pressure on the Arctic and Subarctic regions require modern ecosystem monitoring and understanding of the past environmental changes. Vegetation history is reflected by pollen spectra recorded in peat deposits, investigation of which is one of the main methods in the research of long-term climatic changes. In order to reconstruct the vegetation and fire history of today’s south tundra in the lower reaches of the Taz river, we carried out palynological exploration of peat and underlying lake sediments covering the last 11.2 cal ka BP in the Tazovsky district of the Yamalo-Nenets Autonomous Okrug (Russia). In the course of the research, we found 31 pollen taxa, 4 taxa of spore plants, 2 types of fungal spores, one species of shell amoeba and green algae. We have identified several stages in the development of the local wetland biocenosis at the study site and reconstructed the history of changes in the vegetation cover of the region, including changes in the composition of the woody vegetation. Grasslands, with groups of trees among thickets of shrubs and lake-mire complexes dominated in the study area by 11.2 cal ka BP. The grasslands were gradually supplemented by wet grass communities, which were then replaced by swamps and tundra complexes in the mid-Holocene. The time periods of the local fires have been established. The fire that had the greatest effect on the vegetation at the study site was detected in the period of 8.1 cal ka BP. We have revealed periods of the least fire activity – 7.6–5.5 cal ka BP and the highest fire activity – 12.5–8 cal ka BP.

A New Algivorous Heterolobosean Amoeba, Euplaesiobystra perlucida sp. nov. (Tetramitia, Discoba), Isolated from Pilot-Scale Cultures of Phaeodactylum tricornutum.

The diatom Phaeodactylum tricornutum is regarded as a prospective "cell factory" for the high-value products fucoxanthin and eicosapentaenoic acid (EPA). However, contamination with grazing protozoa is a significant barrier to its commercial cultivation. Here, we describe a new species of heterolobosean amoeba, Euplaesiobystra perlucida, which caused the loss of Phaeodactylum tricornutum in pilot-scale cultures. Morphological and molecular characteristics distinguish E. perlucida from the other species in the genus Euplaesiobystra. E. perlucida is 1.4 to 3.2 times larger than other Euplaesiobystra species in terms of average length/width and maximum length/width of the trophozoites. Unlike Euplaesiobystra salpumilio, E. perlucida has no cytostome; E. perlucida lacks a flagellate stage, whereas Euplaesiobystra hypersalinica and E. salpumilio both display a flagellate stage in their life cycle. The small-subunit rRNA gene sequence of E. perlucida shared only 88.02% homology with that of its closest relative, Euplaesiobystra dzianiensis, and had two distinctive regions. Its phylogenetic branch was clustered with one uncultured heterolobosean clone (bootstrap support/posterior probability = 100%/1.00). Results of feeding experiments demonstrated that E. perlucida could graze on various unicellular and filamentous eukaryotic microalgae (chlorophytes, chrysophytes, euglenids, and diatoms) and cyanobacteria. E. perlucida's ingestion rate declined exponentially with increasing size of unicellular prey, and E. perlucida attained the highest growth rates on P. tricornutum. On the basis of its strong ability to graze on microalgae, capacity to form large populations in a short period of time, and capacity to form resistant resting cysts, this contaminant has the potential to cause severe problems in large-scale microalgal culture and merits further attention. IMPORTANCE Heteroloboseans have garnered considerable interest because of their extraordinary ecological, morphological, and physiological diversity. Many heteroloboseans have adapted to various extensive habitats, including halophilic, acidophilic, thermophilic, psychrophilic, and anaerobic habitats. Most heteroloboseans are bacterivores, with a few algivorous species reported. In this study, a new species of algivorous heterolobosean amoeba, Euplaesiobystra perlucida, is described as a significant grazer that causes losses in outdoor industrial Phaeodactylum cultures. This study provides phenotypic, feeding, and genetic information on a previously unknown heterolobosean, emphasizes the impact of contaminating amoebae in commercial microalgal cultures, and will contribute to the management strategies for predicting this kind of contaminant in large-scale microalgal cultivation.