title: Bacterial flagella rotating in bundles: a study in helical geometry.
abstract: Bacterial flagella are semi-rigid helices that undergo true rotation. In peritrichously flagellated bacteria (e.g., Escherichia and Salmonella) there are many flagella on each cell; during translational cell movement these operate as a coordinated bundle that actively disperses upon reversal of the rotation sense. The dynamic behavior of a set of helices originating on separate rotational axes is explored by a working model, geometrical analysis, and hydrodynamic calculations. A critical relationship exists between the interaxial separation and phase difference of parallel helices with overlapping domains; in the subcritical case the filaments are not intertwisted, whereas in the supercritical case they are intertwisted in the same sense (left-handed) as the helices, with one twist per helical turn. During counter-clockwise rotation (the sense operative in forward swimming) any preexisting twists of this kind are automatically cancelled and the helices brought progressively into phase. Hydrodynamic calculations suggest that some wrapping then occurs in a right-handed sense, opposite to that of the helices; this necessitates a distortion from true helical geometry which is minimized by maintaining a coaxial in-phase relationship. A highly coordinated helical bundle results that is capable of operating smoothly for an indefinite period, in agreement with the observed behavior of swimming bacteria. During reverse rotation, the supercritical case develops to cause jamming of the bundle, as has been observed with bacteria in high-viscosity medium. The explosive dispersal of the bundle during reversal in low-viscosity medium is a consequence of a complicating phenomenon, namely, a drastic change in flagellar quaternary structure. The overall conclusion is that bundle formation and function are perfectly compatible with a rotational mechanism for the individual flagella.
mesh_terms: D018407:Bacterial Physiological Phenomena; D005407:Flagella / Q000502:physiology*; D008954:Models, Biological; D008961:Models, Structural; D009068:Movement
references.citation: Cold Spring Harb Symp Quant Biol. 1953;18:123-31
references.pmid: 13168976
references.citation: J Clin Microbiol. 1976 Sep;4(3):258-65
references.pmid: 823174
references.citation: Proc R Soc Lond B Biol Sci. 1971 Aug 3;178(1052):327-46
references.pmid: 4400008
references.citation: J Bacteriol. 1974 Feb;117(2):696-701
references.pmid: 4204439
references.citation: J Mol Biol. 1974 Apr 15;84(3):399-406
references.pmid: 4618854
references.citation: Science. 1973 Jul 6;181(4094):60-3
references.pmid: 4576832
references.citation: Nature. 1973 Oct 19;245(5425):380-2
references.pmid: 4593496
references.citation: Nature. 1974 May 3;249(452):77-9
references.pmid: 4598032
references.citation: Nature. 1974 May 3;249(452):74-7
references.pmid: 4598031
references.citation: Nature. 1974 May 3;249(452):73-4
references.pmid: 4598030
references.citation: Nature. 1972 Oct 27;239(5374):500-4
references.pmid: 4563019
references.citation: Proc Natl Acad Sci U S A. 1972 Sep;69(9):2509-12
references.pmid: 4560688
references.citation: J Mol Biol. 1972 Jul 21;68(2):347-59
references.pmid: 5069792
references.citation: Adv Biophys. 1970;1:99-155
references.pmid: 4950148
references.citation: Symp Soc Exp Biol. 1968;22:215-36
references.pmid: 4880189
references.citation: J Theor Biol. 1976 Apr;57(2):469-89
references.pmid: 785102