284524 Exploring the Role of Flagella in Bacterial Swarming

Wednesday, October 31, 2012: 1:30 PM
409 (Convention Center )
Douglas B. Weibel, Hannah H. Tuson and Matthew F. Copeland, University of Wisconsin-Madison, Madison, WI

Proteus mirabilis is an opportunistic pathogen that causes urinary tract infections and the biofouling of urinary catheters. A fundamental unanswered question has centered on the mechanism by which this bacterium invades and colonizes the urinary epithelium. Swarming may provide a clue to these infections.

During swarming on nutrient agar in the lab, P. mirabilis becomes morphologically differentiated and is characterized by long (20-100 um long), multinucleate cells that have a remarkably high dense coating of flagella. Back-of-the-envelope calculations of the energy balance in these cells suggests that the assembly and actuation of flagella may account for as much as ~50% of the total energy of the cell. This phenotype is clearly important or it would have been lost long ago.

We explored the physiological and behavior importance of the density of flagella on swarming P. mirabilis cells. By investigating the swimming velocity of different P. mirabilis cell morphologies—each with a different combination of cell length and flagellar density—we discovered that swarmer cells have a larger swimming velocity in solutions with a microviscosity ranging from 10-1000 cP, compared to the other morphologies that we tested. Swarmer cells were motile in fluids with a viscosity that approached ~9000 cP; the motility of all other cells types we studied was inhibited at this viscosity. Overexpression of FlhD4C2—the transcription factor controlling the flagellar gene cascade—increased the swimming velocity of vegetative cells in all of the viscous fluids we tested. Furthermore, FlhD4C2 overexpression rescued vegetative cell motility at ~9000 cP. Both immunofluorescence microscopy and quantitative Western blots demonstrate a correlation between the density of flagella and cell velocity and suggests a threshold density for increasing the velocity of cells in high viscosity fluids. From these data and the reported values for the number of flagella associated with other swarming species, we speculate that an increase in flagellar density may be a universal requirement for swarming motility. Our hypothesis is that the high density of flagella on P. mirabilis may be responsible for cell motility in high viscosity environments, including the mucus secreted by the urinary epithelium, thereby providing a route to infection.

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See more of this Session: Bio-Fluid Dynamics
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