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

JL Ferreira, FZ Gao, FM Rossmann, A Nans… - PLoS …, 2019 - journals.plos.org
JL Ferreira, FZ Gao, FM Rossmann, A Nans, S Brenzinger, R Hosseini, A Wilson, A Briegel
PLoS Biology, 2019journals.plos.org
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 …
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.
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