Item from Project Hail Mary by Andy Weir
The natural predator of the thing eating the Sun — an amoeba that envelops and kills Astrophage, found on a planet twelve light-years from the problem it needed to solve.
Taumoeba is the answer to the mission's central question: why is Tau Ceti the one star that isn't dying? Because something on Adrian eats the thing that eats the stars. The natural Taumoeba population keeps Tau Ceti's Astrophage in check through simple predator-prey dynamics — the same ecological balance that prevents any single species from consuming everything on Earth. The complication is nitrogen. Natural Taumoeba dies in the presence of nitrogen, which means it can't survive on Venus (Earth's Astrophage breeding ground) or Threeworld (Erid's equivalent). Grace and Rocky breed a nitrogen-resistant strain — Taumoeba-82.5 — through eighty-two and a half rounds of selective evolution. But engineered organisms don't always behave as designed: strain 82.5 develops the ability to penetrate xenonite, which natural Taumoeba cannot do. This means the engineered cure could eat through Rocky's xenonite ship and fuel tanks, turning the solution into a new catastrophe.
An amorphous, amoeba-like microorganism — shapeless and unremarkable under microscopy. It envelops Astrophage cells and kills them through a process that dissolves the Astrophage's energy-storage mechanism. Individually tiny; collectively, the reason Tau Ceti's sun still shines.
Also known as: Taumoeba, Taumoeba-82.5, The Cure