| dc.description.abstract | Bacterial flagella are thin external tubular filaments that form helical propellers to drive swimming in bacteria. Forming flagella is a self-assembly process when partially unfolded flagellum monomers, flagellins, are pumped out and transported through the central channel from its base to the distal end. The secretion apparatus contains six membrane proteins (FlhA, FlhB, FliO, FliP, FliQ and FliR) and three
soluble proteins (FliH, FliI, and FliJ) shareing the same structure with type III secretion system which is used solely for secretion. As flagellin reaches the growing
end of flagellar filament, it crystallizes immediately and becomes the new extending part of the filament. In order to study this nanometer-size self-assembled system, we have developed a fast flagellar filament labeling assay. We applied in vivo fluorescent imaging to monitor directly the growth of Vibrio alginolyticus polar flagella with high
spatial and temporal resolution. In contrast to previous reports, we revealed that the flagellar growth rate of Vibrio alginolyticus is highly length-dependent. When
flagellar length is shorter than 1500 nm, the flagellum growth is at a constant rate (50 nm/min). As the flagellum grows longer, the growth rate decays. It drops sharply at
first and tends to ease in the long flagella region. It decreases to 9 nm/min when flagellar length is 7500 nm. We built an injection-diffusion model to explain our results. When the flagellum is short, its growth rate is determined primarily by the loading speed at the filament base, since diffusion of flagellin across the short distance in the channel is fast. When the flagellum grows longer, diffusion of flagellin becomes rate-limiting. It causes some flagellar monomers jammed in the channel.
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Such blockage slows down the loading of new flagellins into the channel. Therefore,the flagellar growth rate drops dramatically. Our results shed new light on the dynamic building process of this complex extracellular structure. | en_US |