A cannibalistic microbe that can transform into a "supergiant" predator—and swallow its own kin—has been discovered in a seawater filter on the Caribbean island of Curaçao.
Discovery and Basic Characteristics
The newly identified single-celled microbe, Euplotes gigatrox, was isolated from a seawater filtration system. In its normal state, it measures approximately 54 micrometers in length, feeds on bacteria, and moves by walking across surfaces or swimming gracefully along helical trajectories.
Supergiant Transformation
Clones of the microbe can spontaneously develop into a form researchers have termed "supergiants." These supergiant cells can exceed twice the length of normal cells, reaching up to 140 micrometers, and possess a broader body and larger mouth. This transformation occurs after population growth stabilizes and bacterial food sources become scarce, indicating a response to changing resource availability.
The supergiant form is a distinct developmental stage characterized by widespread differences in gene activity, including protein production and membrane organization. When supergiants revert to their normal size—a process that occurs within 24 hours—they enter a refractory period. Cells that have recently reverted carry a distinct set of molecules that appear to temporarily suppress transformation back into the supergiant state. Analysis of gene expression revealed one set of genes active during supergiant formation and another set active in reverted cells, which may be responsible for this latency period.
Behavioral Changes
As supergiants, E. gigatrox shifts from filter-feeding on bacteria to active predation. They hunt along surfaces, capturing and swallowing clonal relatives whole at an observed rate of approximately one prey every 10 minutes. Their movement pattern changes to circular paths suited to hunting surface-crawling prey, and they tumble clumsily when displaced from a surface. In contrast, normal cells can swim freely. The supergiant proportion never exceeded 5% of the population in laboratory cultures.
Significance
The phenomenon was documented in seawater samples cultured in artificial seawater with bacteria. According to co-author Ben Larson, a biologist at Rensselaer Polytechnic Institute, the supergiant formation represents a shift in trophic niche. The research was published in Proceedings of the National Academy of Sciences.