A microbe is a microscopic organism, and it is not necessarily within a unified group that is closely related. In fact, microbes exist in all three domains of life. There are microbes that are bacteria, microbes that are archaea, and microbes that are part of the more complex domain that plants and animals are a part of—the eukaryotes. Even viruses, a group scientists debate is even a form of life, are considered to be microbes. Microbes are incredibly diverse and live in bustling microscopic worlds that are invisible to our eyes.

This work was supported by the National Academies Keck Futures Initiative of the National Academy of Sciences under award number NAKFI DBS17. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Academies Keck Futures Initiative or the National Academy of Sciences.