Some scientists believe that nanobes are the smallest living organisms. They are 20-150 billionths of a meter (10-12 to 10-13), and smaller than any known bacteria, spore or other single-celled organism.
In 2004, a team at the Mayo Clinic in Rochester, Minnestota presented four years of research on nanobes. They claimed that they may cause a diverse range of diseases, including the calcification of the arteries that affects us as we get older. However, some say nanobes are too small to be living organisms. It’s questionable whether or not they even contain the necessary cell components, such as DNA, RNA, and plasmids. To learn more, check out this article in Astrobiology Magazine.