Euplotes gigatrox, a new species of ciliate collected from a seawater filtration system on the Caribbean Island of Curaçao, can transform into a cannibalistic ‘supergiant,’ raising new questions about the complexity of life at the microscopic scale.
Euplotes gigatrox. Image credit: Ben Larson & Samuel Lord.
“Ciliates of the genus Euplotes have attracted attention since the earliest days of microscopy, due to their ubiquity and striking features,” said lead author Dr. Ben Larson from the Rensselaer Polytechnic Institute and colleagues.
“Euplotes species occur in most aquatic ecosystems, and their movement, mating habits, symbiotic relationships, biogeography, and adaptations to local environments have all been extensively investigated.”
“Euplotes cells have a highly ordered, complex animal-like body plan, with cilia packed into larger structures, called membranelles and cirri, that have been modified for feeding (by generating water currents), swimming, or to be used as ‘legs’ for walking across substrates.”
Named Euplotes gigatrox, the new member of the genus was collected from a seawater filtration system on the Caribbean Island of Curaçao.
In clonal populations of these organisms where every cell shares the same DNA, a small number of cells can spontaneously develop into supergiants more than twice the length of normal cells, with a broader body shape and a larger mouth.
Rather than filter-feeding on bacteria as normal cells do, supergiants become raptorial predators, running over smaller clonal relatives to capture and swallow them whole, at a rate of roughly one prey every ten minutes.
“This is a single cell doing something we usually associate with the development of animals,” Dr. Larson said.
“It expands our picture of what single-celled organisms are capable of, and gives us a new system for asking questions about how cells control their form and function.”
According to the team, the behavioral shift runs deeper than feeding alone.
Normal cells walk across surfaces and swim gracefully along helical trajectories in fluid.
Supergiants only walk, moving in circular paths suited to hunting surface-crawling prey, and tumble clumsily rather than swim when displaced from a surface.
“Supergiant formation represents a tradeoff. These cells become better hunters but worse swimmers, shifting their trophic niche from feeding on bacteria to exploiting a completely different type of prey,” Dr. Larson said.
To investigate the molecular basis of the transformation, the authors sequenced single-cell transcriptomes from Euplotes gigatrox’s normal cells, supergiants, and cells that had recently reverted from the supergiant state.
The results showed that the supergiants are a transcriptionally distinct developmental stage, with widespread differences in gene expression including cell cycle regulation, protein production, and membrane organization.
Cells that revert from the supergiant state also carry a distinct molecular signature, one that appears to temporarily suppress the pathways driving transformation.
Populations started from recently reverted cells produced new supergiants more slowly and at lower overall frequency than populations started from normal cells, regardless of external conditions.
Supergiant formation tends to occur as populations transition from rapid growth to stationary phase, particularly when small prey is not too abundant, and they only persist while small prey remains scarce and large prey (normal cells) are present.
Supergiants never exceed about 5% of the population, consistent with a bet-hedging strategy in which a small fraction of cells shifts to exploit a different resource.
The findings provide a new framework for studying development in unicellular organisms, which must carry out all the functions of both a cell and an entire organism within a single membrane.
“Most of what we know about development comes from animals,” Dr. Larson said.
“We now have a system where we can study those same fundamental questions, as analogous developmental processes play out in a single-celled organism on a completely different branch of the tree of life.”
The study appears in the 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
