Biogenesis of Polar Flagella Motors

In contrast peritrichous motile bacterial species that produce flagellar motors over the cell surface, other motile bacteria produce a very limited number of flagellar motors only at the poles of the bacterial cell. These polar flagellar motors often promote higher velocities of swimming motility in viscous substances that can paralyze peritrichously-flagellated bacteria.

Electron cryotomographical analysis of flagellar motors of Salmonella and Campylobacter jejuni

Through an exciting collaboration with the laboratory of Dr. Morgan Beeby at Imperial College in London, we are combining traditional approaches such as genetic screens, biochemical analysis of proteins, and transmission electron microscopy and innovative technologies including electron cryotomography to determine the composition and structure of polar flagellar motors. Through transposon mutagenesis, deletion analysis of specific genes, and protein-interactions assays, we are identifying new proteins required for motility in polarly-flagellated bacteria. We then apply transmission electron microscopy to determine whether polar flagellar motors are constructed, appropriately sized, and correctly placed on the bacterial cell of various bacterial mutants. Electron cryotomography can provide an average three-dimensional image, or tomogram, of the macromolecular structure of an intact flagellar motor in frozen-hydrated bacterial cells at low-nanometer resolution. Comparative analysis of the tomograms of polar flagellar motors from isogenic bacterial mutants can reveal the position of specific proteins or complexes within a flagellar motor. Our initial analysis has revealed that polar flagellar motors are often more complex and display greater diversity in structural composition relative to many peritrichous flagellar motors. 

We have analyzed the polar flagellar motors of Campylobacter jejuni and identified new structures associated within the motor of this bacterium. We are currently determining the functions of these unique structures of the C. jejuni flagellar motor and how they may contribute to forming a motor able to propel the bacterium with a high velocity of swimming motility through viscous milieu. These motile properties are likely relevant for movement through substances that the bacterium normally contacts, such as the thick mucus layer atop the epithelium of the intestinal tract in the human or avian host. We have extended our analysis into the flagellar motors of other polar flagellates, which will likely reveal new, exciting features of polar flagellar motors and how they function for motility.

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