microbiology (n.)

word-forming element meaning "small in size or extent, microscopic; magnifying;" in science indicating a unit one millionth of the unit it is prefixed to; from Latinized form of mikros, Attic form of Greek smikros "small, little, petty, trivial, slight," perhaps from PIE *smika, from root *smik- "small" (source also of Old High German smahi "littleness"), but Beekes thinks it a Pre-Greek word.

"the science of life and living things," 1819, from Greek bios "life, one's life, lifetime" (from PIE root *gwei- "to live;" see bio-) + -logy "study of." Suggested 1802 by German naturalist Gottfried Reinhold Treviranus, and introduced as a scientific term that year in French by Lamarck; they seem to have hit upon the word independently.

"one who studies or is versed in the knowledge of microbes," 1882, from microbiology + -ist.