Figure 5.

Proposed model for the evolution of the bacterial flagellar motor inferred from ECT and STA data. ECT and STA have indicated multiple pathways for the acquisition of additional accessory proteins resulting in improved stator support, increased outer membrane support and finally, in the case of C. jejuni, a basal disk–proximal disk fusion. ECT has also revealed structural and evolutionary insights into degenerate flagellar motors that have become injectisomes: virulence-factor delivery systems that are used by many pathogenic bacteria. Ancestral states have been inferred from representative subtomogram averages on the right coupled with phylogenetic studies (Chaban et al., 2018 ▸; Beeby et al., 2016 ▸).