title: The maximum number of torque-generating units in the flagellar motor of Escherichia coli is at least 11.
abstract: Torque is generated in the rotary motor at the base of the bacterial flagellum by ion translocating stator units anchored to the peptidoglycan cell wall. Stator units are composed of the proteins MotA and MotB in proton-driven motors, and they are composed of PomA and PomB in sodium-driven motors. Strains of Escherichia coli lacking functional stator proteins produce flagella that do not rotate, and induced expression of the missing proteins leads to restoration of motor rotation in discrete speed increments, a process known as "resurrection." Early work suggested a maximum of eight units. More recent indications that WT motors may contain more than eight units, based on recovery of disrupted motors, are inconclusive. Here we demonstrate conclusively that the maximum number of units in a motor is at least 11. Using back-focal-plane interferometry of 1-mum polystyrene beads attached to flagella, we observed at least 11 distinct speed increments during resurrection with three different combinations of stator proteins in E. coli. The average torques generated by a single unit and a fully induced motor were lower than previous estimates. Speed increments at high numbers of units are smaller than those at low numbers, indicating that not all units in a fully induced motor are equivalent.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, South Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Stuart W
authors.initials: SW
authors.lastname: Reid
authors.forename: Mark C
authors.initials: MC
authors.lastname: Leake
authors.forename: Jennifer H
authors.initials: JH
authors.lastname: Chandler
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Lo
authors.forename: Judith P
authors.initials: JP
authors.lastname: Armitage
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001703:Biophysics / Q000379:methods; D002478:Cells, Cultured; D004926:Escherichia coli / Q000378:metabolism*; D005407:Flagella / Q000502:physiology*; D005838:Genotype; D008954:Models, Biological; D020409:Molecular Motor Proteins; D016011:Normal Distribution; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D019415:Torque
chemical_list: D001426:Bacterial Proteins; D020409:Molecular Motor Proteins; C063010:MotA protein, Bacteria; C064779:MotB protein, Bacteria