Figure 4
From: Evolution of higher torque in Campylobacter-type bacterial flagellar motors
Proposed model of bacterial flagellar motor disk complex evolution. Evolving from a basic motor (bottom left), the incremental addition of proteins has on multiple independent occasions led to the assembly of inner membrane support structures (boxed in green) and outer membrane support structures (boxed in blue). In the ε-proteobacteria, these two structures have fused to form a scaffold structure (boxed in pink). Sub-tomogram averages on the right show contemporary motors that exemplify descendants of each ancestral intermediate.
