Physics (Internal)

Investigating Effects of Morphology and Flagella Dynamics on Swimming Kinematics of Different Helicobacter Species Using Single Cell Imaging

This event is part of the PhD Final Oral Exams.

Examining Committee: Rama Bansil, Shyam Erramilli, Kirill Korolev, Karl Ludwig, Kevin Black

Abstract:

This work explores the effects of body shape and configuration of flagella on motility of Helicobacter pylori, a helical-shaped bacterium that inhabits the viscoelastic gastric mucosa and causes gastritis, ulcers and gastric cancer. Although it is well known that different shapes produce different hydrodynamic drag thus altering the speed and that helical shapes generate additional thrust this has not been quantitatively established for flagellated bacteria. Using fast time-resolution and high-magnification two-dimensional phase-contrast microscopy to simultaneously image and track individual helical-shaped H. pylori and its rod-shaped isogenic mutant in broth and mucin solutions, the shape as well as rotational and translational speed can be determined. Henry Fu and Mehdi Jabbarzadeh used the experimental data to validate the method of regularized Stokeslets by directly comparing the observed speeds to numerical calculations. The results show that due to relatively slow body rotation rates, the helical shape makes at most a 15% contribution to speeds. In order to explore the effects of flagella configuration on motility, three members of the Helicobacter species were examined: H. suis (bipolar, multiple flagella), H. cetorum (bipolar, single flagellum) and H. pylori (unipolar, multiple flagella). Due to the large number of flagella in each pole, the flagellar bundle of H. suis could be visualized while it swam in broth and mucin. Results show that regardless of media, the flagella bundles can assume one of two configurations interchangeably: extended away from the body or wrapped around it. H. suis predominantly swims with the lagging flagella extended behind the body and the leading flagella wrapped around it, but cases where both bundles are extended or both are wrapped have also been observed. Using the same experimental technique described earlier, the results show that bipolar bacteria gain a speed advantage over unipolar bacteria. In addition, the effects of pH on motility of H. suis in broth and mucin were investigated. Similarly to previous findings on H. pylori, the results show that H. suis swims faster in mucin than broth at same pH and that it stops swimming in mucin at pH4 due to gelation.