Evolution of a large periplasmic disk inCampylobacterotaflagella facilitated efficient motility alongside autoagglutination

Abstract

SummaryAlthough the bacterial flagella ofEscherichia coliandSalmonella entericaare distributed around the cell body, many bacteria instead place their flagella at their poles. This widespread form of flagellar motility is relatively poorly understood, but these polar flagellar motors invariably feature periplasmic disk structures of unknown function. The flagellar motor ofCampylobacter jejunifeatures a 100 nm-wide periplasmic disk associated with scaffolding a wider ring of motor proteins to increase torque, but the size of this disk is excessive for a role solely in scaffolding motor proteins. Here we show that the basal disk inC. jejuniis a flange that braces the motor during disentanglement of the flagellar filament from interactions with the cell body and other filaments, interactions that are otherwise important for host colonization. Our results reveal an entanglement of co-dependencies in the evolution of flagellar motor structure and cell plan in the Campylobacterota (previously epsilonproteobacteria). Note that this manuscript has a sibling manuscript titled’Molecular model of a bacterial flagellar motor in situ reveals a “parts-list” of protein adaptations to increase torque’that describes a molecular model of theCampylobacter jejuniflagellar motor discussed here.