Dynamic production and loss of flagellar filaments during the bacterial life cycle

Bacterial flagella are large extracellular protein organelles that drive bacteria motility and taxis in response to environmental changes. Previous research has focused mostly on describing the flagellar assembly, its rotation speed and power output. However, whether flagella are permanent cell structures and, if not, the circumstances and timing of their production and loss during the bacterial life cycle remain poorly understood. Here we used the single polar flagellum of Vibrio alginolyticus as our model and, using in vivo fluorescence imaging, revealed that the percentage of flagellated bacteria (PFB) in a population varies substantially across different bacterial growth phases. In the early-exponential phase, the PFB increases rapidly in respect to incubation time, mostly through widespread flagella production. In the mid-exponential phase, the PFB peaks at around 76% and the partitioning of flagella between the daughter cells is 1:1 and strictly at the old poles. After entering the stationary phase, the PFB starts to decline, mainly because daughter cells stop making new flagella after cell division. Interestingly, we discovered that bacteria can actively abandon flagella after prolonged stationary culturing, though cell division has long been suspended. Lack of glucose was found to be a major factor promoting flagellar disassembly. We also revealed that the active loss of flagella was initiated by breakage in the rod connecting the extracellular filament to the basal body formed by MS- and C-rings. Our results highlight the dynamic production and loss of flagellar filaments during the bacterial life cycle.