γ-proteobacteria eject their polar flagella under nutrient depletion, retaining flagellar motor relic structures

PLoS Biol. 2019 Mar 19;17(3):e3000165. doi: 10.1371/journal.pbio.3000165. eCollection 2019 Mar.

Abstract

Bacteria switch only intermittently to motile planktonic lifestyles under favorable conditions. Under chronic nutrient deprivation, however, bacteria orchestrate a switch to stationary phase, conserving energy by altering metabolism and stopping motility. About two-thirds of bacteria use flagella to swim, but how bacteria deactivate this large molecular machine remains unclear. Here, we describe the previously unreported ejection of polar motors by γ-proteobacteria. We show that these bacteria eject their flagella at the base of the flagellar hook when nutrients are depleted, leaving a relic of a former flagellar motor in the outer membrane. Subtomogram averages of the full motor and relic reveal that this is an active process, as a plug protein appears in the relic, likely to prevent leakage across their outer membrane; furthermore, we show that ejection is triggered only under nutritional depletion and is independent of the filament as a possible mechanosensor. We show that filament ejection is a widespread phenomenon demonstrated by the appearance of relic structures in diverse γ-proteobacteria including Plesiomonas shigelloides, Vibrio cholerae, Vibrio fischeri, Shewanella putrefaciens, and Pseudomonas aeruginosa. While the molecular details remain to be determined, our results demonstrate a novel mechanism for bacteria to halt costly motility when nutrients become scarce.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Flagella / metabolism
  • Gammaproteobacteria / metabolism
  • Gammaproteobacteria / pathogenicity*
  • Plesiomonas / metabolism
  • Plesiomonas / pathogenicity
  • Pseudomonas aeruginosa / metabolism
  • Pseudomonas aeruginosa / pathogenicity
  • Shewanella putrefaciens / metabolism
  • Shewanella putrefaciens / pathogenicity
  • Vibrio cholerae / metabolism
  • Vibrio cholerae / pathogenicity