Taumoeba

Taumoeba is a species of amoeba-like alien microbe native to the atmosphere of Tau Ceti e, or Adrian. It is most notable as the sole natural predator of Astrophage.

Description
Taumoeba is an amoebic single-celled organism many times larger than Astrophage, probably some hundreds of microns in diameter. In most respects it resembles a terrestrial eukaryotic cell. It is implied to be a methanogen, respiring carbon dioxide into methane for energy.

Diet
Taumoeba feeds exclusively on Astrophage. It consumes Astrophage by engulfing Astrophage cells either individually or in small groups, then killing and digesting them. Taumoeba is apparently able to neutralize Astrophage’s radiant propulsion, which would otherwise allow Astrophage to easily escape a predator.

Environment
Taumoeba naturally lives in the upper atmosphere of Adrian, where Astrophage breed. Here, at an altitude of 91 kilometers, atmospheric pressure is 0.02 bar and the temperature is negative 51 degrees Celsius. Since Astrophage, at 96 degrees Celsius, is far hotter than this, Taumoeba must necessarily have a tolerance for both extreme heat and extreme cold. Taumoeba can tolerate an incredibly wide range of temperatures, from 104 degrees Celsius to negative 180 degrees Celsius.

Taumoeba can survive in virtually any atmosphere so long as it contains carbon dioxide. Nitrogen, however, is extremely poisonous to Taumoeba, so much so that any measurable amount of nitrogen will almost immediately kill it. It is unclear how or why nitrogen poisons Taumoeba - Grace and Rocky both note this as very odd, since nitrogen is mostly non-reactive, but do not have the time to explore it.