A low-angle X-ray diffraction study of bacterial flagella

In order to differentiate between the various proposed models for the structure bacterial flagella, low-angle X-ray diffraction studies have been carried out on wet specimens of Proteus vulgaris. The low-angle equatorial diffraction pattern has been obtained and compared with the theoretically calculated patterns for a rod model and the double and triple helical structures according to Labaw and Mosley. The comparison shows that a model comprised of helical filaments is the most likely structure. Fourier-Bessel transformation of the experimental scattering data has been performed and the radial density-distribution curve gives low values in the middle of the structure, suggesting the flagellum has a hollow center, thus favouring the triple helical form.