Microscopic civilization
A microscopic civilization was any civilization that consisted of sentient microbes.

In 2381, when Ensign Sam Rutherford was obsessing over how Lieutenant Shaxs came back from the dead, he imagined several possibilities that could have brought him back.

One of the things that he imagined was that a microscopic civilization brought him back to harness the  of his body with a tiny Dyson sphere. ()

Microorganisms