Ben Larson, Samuel Lord.
Euplotes gigatrox
A new species of ciliate shows that single-celled organisms can adopt much more complex survival strategies than previously thought, alternating between different ways of life depending on the availability of food.
O Euplotes gigatrox, a species of ciliate recently collected in a seawater filtration system on the island of Curaçao, in the Caribbean, manages to transform into a “supergiant” cannibalraising new questions about the complexity of life on a microscopic scale.
The species now discovered was presented in a published in Proceedings of the National Academy of Sciences.
“The ciliates of the genus Euplotes attract attention from the beginning of microscopy, due to its ubiquity and its striking characteristics”, write Ben Larsonof Rensselaer Polytechnic Institute, and his colleagues in the study.
Euplotes species occur in most aquatic ecosystems, and their locomotion, mating habits, symbiotic relationshipsbiogeography and adaptations to local environments have been the subject of in-depth research, say the study authors.
Euplotes cells have a highly organized body plan and complex, similar to that of an animal, with cilia grouped into larger structures, called membranellas and cirri, which were modified for foodthrough the generation of water currents, for swimming or to function as ‘legs’ when moving over substrates, the researchers add.
Baptism Euplotes gigatroxthe new member of the genus was collected in a seawater filtration system on the Caribbean island of Curaçao.
In clonal populations of these organisms, in which all cells share the same DNA, a small number of cells can develop spontaneously in supergiants more than twice as long of normal cells, a wider body shape and a larger mouth.
Instead of feeding by filtering bacteria, as normal cells do, supergiants become raptorial predators: They advance on smaller clonal relatives to capture and swallow them whole, at a rate of about one prey every ten minutes.
“It is about a simple cell doing something that we normally associate with animal development” said Larson. “This broadens our view 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, behavioral change goes far beyond food. normal cells move over surfaces and swim elegantly in fluids following helical trajectories.
Supergiants just walkmoving in circular paths suitable for hunting prey that crawl on surfaces, and, when they are moved away from a surface, they roll awkwardly instead of swimming.
“The formation of supergiants represents a commitment. These cells become best hunters, but worst swimmersshifting its trophic niche from feeding on bacteria to exploring a completely different type of prey”, explains Larson, cited by .
The cells that revert from supergiant state also present a own molecular signaturewhich appears to temporarily suppress the pathways responsible for transformation.
Populations started from recently reverted cells produced new supergiants slower and with a lower overall frequency than populations initiated from normal cells, regardless of external conditions.
The formation of supergiants tends to occur when populations pass from one rapid growth phase to a stationary phaseespecially when the Small prey is not too abundants, and these only persist as long as small prey remains sparse and large prey (normal cells) are available.
Supergiants never exceed around 5% of the populationwhich is compatible with a risk diversification strategyin which a small fraction of cells starts to exploit a different resource.
The findings provide a new framework for studying development in single-celled organisms, which must perform all the functions of a cell and an entire organism within a single membrane.
“Most of what we know about development comes from animals” said Larson. “We now have a system in which we can study the same fundamental questions, in analogous developmental processes that occur in a single-celled organism of a completely different branch of the tree of life.”
