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

Abstract

23Bacterial flagella are large extracellular protein organelles that drive bacteria motility 24 and taxis in response to environmental changes. Previous research has focused mostly 25 on describing the flagellar assembly, its rotation speed and power output. However, 26 whether flagella are permanent cell structures and, if not, the circumstances and timing 27 of their production and loss during the bacterial life cycle remain poorly understood. 28 Here we used the single polar flagellum of Vibrio alginolyticus as our model and, using 29 in vivo fluorescence imaging, revealed that the percentage of flagellated bacteria (PFB) 30 in a population varies substantially across different bacterial growth phases. In the 31 early-exponential phase, the PFB increases rapidly in respect to incubation time, mostly 32 through widespread flagella production. In the mid-exponential phase, the PFB peaks 33 at around 76% and the partitioning of flagella between the daughter cells is 1:1 and 34 strictly at the old poles. After entering the stationary phase, the PFB starts to decline, 35 mainly because daughter cells stop making new flagella after cell division. Interestingly, 36 we discovered that bacteria can actively abandon flagella after prolonged stationary 37 culturing, though cell division has long been suspended. Lack of glucose was found to 38 be a major factor promoting flagellar disassembly. We also revealed that the active loss 39 of flagella was initiated by breakage in the rod connecting the extracellular filament to 40 the basal body formed by MS-and C-rings. Our results highlight the dynamic 41 production and loss of flagellar filaments during the bacterial life cycle.42 43 Main Text 44 3 The flagellum of a flagellated bacterium is a remarkable structure consisting of a 45 reversible rotary motor, a short proximal hook, and a thin helical filament [1]. Since the 46 flagellar system was discovered, this delicate nanomachine has attracted much research 47 and, while some aspects of the flagellar system have been well studied, others have not 48 [2-6]. Meanwhile, flagella are not only critical for bacterial motility, their constituent 49 flagellins are also important antigens that can stimulate both the innate inflammatory 50 response and the development of adaptive immunity [7-9]. Two specialized receptors 51 on immune cells, cell surface Toll-like receptor 5 (TLR5) [10-12] and intracellular 52 receptor Ipaf [13, 14], are responsible for recognizing flagellins as a warning of a 53 pathogenic bacterial invasion. Knowing when and how bacteria produce and lose 54 flagella, especially under stressed conditions, is valuable for understanding the way 55 bacteria either trigger or evade host immunity surveillance, a central topic in pathogen-56 host interactions. 57 Previous research has shown that bacterial flagella are hollow protein cylinders 58 with 20 nm outer and 2 nm inner diameters [15]. A flagellum is assembled from the 59 inside out, beginning with a basal body embedded in the cell membrane and...

Bacterial flagellar motor PL-ring disassembly subcomplexes are widespread and ancient

“…Much less is known about the process of flagellar disassembly, though it is known that Caulobacter crescentus loses its flagellum and pili at a specific stage of its life cycle (15). We and others also recently reported that different Gammaproteobacteria species lose their flagella when starving or due to mechanical stress (7,(16)(17)(18). Interestingly, in situ imaging using cryoelectron tomography (cryo-ET) showed that this disassembly process leaves an outer-membrane-associated relic subcomplex consisting of the decorated flagellar P and L rings (referred to henceforth as PL-subcomplexes).…”

Pseudomonas aeruginosa PAO 1 In Vitro Time–Kill Kinetics Using Single Phages and Phage Formulations—Modulating Death, Adaptation, and Resistance

“…Flagella are not permanent cellular structures; instead, the cell's probability of having a flagellum differs across different growth phases [41]. Bacteria without flagella generally cause less inflammation and mortality [42,43]. The swimming motility of the survivors varied according to the phage(s) used, and higher losses in motility were achieved in treatments with the 5PCF and the SMS12 + SMS21 cocktails, presenting 73.7 and 71.4% of nonswimmers, respectively.…”