Bacteria, Viruses, and Protists

Bacteria Basics

Are any bacteria visible to the naked eye?

Epulopiscium fishelsoni, bacteria that live in the gut of the brown surgeonfish (Acanthurus nigrofuscus), are visible to the naked eye. It was first identified in 1985 and mistakenly classified as a protozoan (mostly aquatic, single-celled organisms; for more about protozoa, see this chapter). Later studies analyzed the organism’s genetic material that showed it to be a bacterium of unprecedented size: 0.015 inches (0.38 millimeter) in diameter—about the size of a period at the end of this sentence.


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