A newly identified ciliate species, designated Euplotes gigatrox, has been discovered in a seawater filtration apparatus situated on the Caribbean island of Curaçao. This organism’s remarkable capacity to transform into a voracious “supergiant” form prompts novel inquiries into the intricate nature of life at the microscopic level.
Euplotes gigatrox. Image credit: Ben Larson & Samuel Lord.
“Forerunners in the field of microscopy have long been captivated by ciliates belonging to the genus Euplotes, owing to their pervasive presence and distinctive characteristics,” stated lead author Dr. Ben Larson of Rensselaer Polytechnic Institute, alongside his research collaborators.
“Euplotes species are prevalent across the vast majority of aquatic environments, and their modes of locomotion, reproductive behaviors, symbiotic associations, geographical distribution, and evolutionary adaptations to specific habitats have been the subject of extensive scientific scrutiny.”
“Within the Euplotes genus, cells exhibit a highly organized and sophisticated body plan, reminiscent of animal structures. Their cilia are aggregated into larger formations, termed membranelles and cirri, which have been specialized for functions such as feeding by generating water currents, facilitating propulsion through swimming, or serving as appendages for adhering to and traversing surfaces akin to legs.”
The recent addition to this genus, christened Euplotes gigatrox, was isolated from the seawater filtration system located on Curaçao, a Caribbean island.
Within populations of these organisms that are clonally derived—meaning every individual shares identical genetic material—a subset of cells can spontaneously undergo a metamorphosis into “supergiants.” These transformed cells are more than twice the standard length of regular cells, possess a wider bodily contour, and feature an enlarged oral apparatus.
Instead of the filter-feeding behavior on bacteria characteristic of normal cells, the supergiants adopt predatory strategies. They actively traverse their clonal relatives, capturing and ingesting them whole at an approximate rate of one individual every ten minutes.
“This represents a single-celled organism engaging in a process typically associated with the developmental trajectory of multicellular animals,” commented Dr. Larson.
“It significantly broadens our understanding of the capabilities inherent in single-celled life forms and furnishes us with a novel model system for investigating the mechanisms by which cells regulate their morphology and physiological functions.”
The research team indicated that the shift in behavior extends beyond mere dietary alterations.
Undifferentiated cells navigate surfaces and exhibit graceful helical movement through liquid mediums.
Supergiants, in contrast, exclusively ambulate, following circular paths optimized for hunting prey that crawls on surfaces. When dislodged from a substrate, they tumble rather than swim.
“The development of supergiants necessitates a trade-off. While these cells gain enhanced predatory skills, their aquatic mobility is compromised, leading to a repositioning within the food web from consuming bacteria to exploiting an entirely different food source,” explained Dr. Larson.
In an effort to elucidate the molecular underpinnings of this transformative process, the researchers performed single-cell transcriptome sequencing on normal Euplotes gigatrox cells, their supergiant counterparts, and cells that had recently reverted from the supergiant phenotype.
The findings revealed that supergiants represent a transcriptionally distinct developmental phase, characterized by pervasive alterations in gene expression patterns governing cell cycle regulation, protein synthesis, and membrane organization.
Cells that revert from the supergiant form also exhibit a unique molecular signature, which appears to transiently inhibit the molecular pathways that drive the transformation.
Populations initiated from recently reverted cells demonstrated a reduced rate and overall frequency of new supergiant formation compared to populations originating from normal cells, irrespective of external environmental conditions.
The emergence of supergiants is typically observed as populations transition from a phase of accelerated proliferation into a stationary growth phase, particularly when preferred microscopic prey is not abundant. These supergiant forms persist only in circumstances where small prey remains scarce and larger prey (normal cells) are available.
Supergiants constitute no more than approximately 5% of the total population, a proportion consistent with a bet-hedging strategy, where a small fraction of the population diversifies its resource utilization.
These discoveries establish a new paradigm for the study of development in unicellular organisms, which are tasked with undertaking all the essential functions of both a cell and a complete organism within a singular cellular boundary.
“Our current comprehension of biological development is predominantly derived from the study of animals,” Dr. Larson remarked.
“We now possess a model system that enables the investigation of these fundamental developmental questions within a unicellular organism, a creature that operates on a significantly divergent branch of the evolutionary tree of life, yet exhibits analogous developmental processes.”
The research findings are published in the journal Proceedings of the National Academy of Sciences.
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Ben T. Larson et al. 2026. Regulated development of cannibalistic supergiant cells in the ciliate Euplotes gigatrox. PNAS 123 (20): e2606891123; doi: 10.1073/pnas.2606891123
