Evolution of the bacterial flagellum

Abstract

• Bacterial flagella are modular structures consisting of (1) a basal body, (2) a filamentous propeller, (3) an interconnecting hook complex, (4) a rotary motor, (5) a secretion/assembly system, (6) a secretion energizing ATPase, and (7) various ancillary proteins. • Each module probably evolved independently of the others from primordial systems having nothing to do with cell motility. • Complexity arose by domain and protein recruitment as well as by intragenic and extragenic duplication events. • Hundreds of structurally and functionally distinct flagella, present in various bacterial species, share only about half their protein constituents.