How bacteria swim

Bacterial flagella in the light microscope, left:
Desulfovibrio sapovorans, right: Desulfovibrio desulfuricans
A bacterial flagellum is only 0.01 µm thick and not directly visible in the light microscope. However, by treatment with a contrasting agent (tannin) the flagella can be made thicker, until they become visible. Often the flagella loose their natural curling during this procedure.

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