Flagellum, shift into reverse gear! https://schaechter.asmblog.org/schaechter/2024/05/hey-flagellum-shift-into-reverse-gear.html

Structural basis of directional switching by the bacterial flagellum https://pubmed.ncbi.nlm.nih.gov/38459206/

"In a manual gearbox, a gearwheel is inserted between the countershaft and the drive shaft. This reverses the rotation. #Flagella of E. coli, Salmonella #bacteria have found a smart solution to do without an additional wheel: they run their engine along the outside of a gearwheel or, if they reverse the direction of rotation, on its inside"