Physics (Internal)

Mobility of Helicobacter Pylori in Gels

This event is part of the Preliminary Oral Exam.

Examining Committee:  Rama Bansil, Steve Ahlen, Shyam Erramilli, Pankaj Mehta Helicobacter Pylori, a helical bacterium with multiple polar flagella, colonizes the low pH gel environment of the human stomach and can cause gastric ulcers, gastritis and cancer.  The issue of how it moves in a viscoelastic gel is central to establishing an infection. Two factors are believed to play a role in helping it deal with the low pH gel environment.  In earlier work from our laboratory Celli et al showed that this bacteria secretes urease which breaks down urea to produce NH₃ leading to elevation of pH and triggering a gel-sol transition in the mucin gel¹.  This significantly decreases the viscoelastic nature of the environment allowing the bacteria to swim freely.  In this presentation I will address whether its helical body allows it to swim more effectively in viscoelastic environments.  In order to study the effects of body shape on motility we have compared the wild type (helical) with straight rod mutants in gelatin solutions undergoing a sol –gel transformation.  Gelatin allows for control of the gel properties using temperature and concentration while keeping the solution at suitable pH for the bacteria.  Using video microscopy I have tracked the bacteria at different stages of the sol – gel transition and been able to identify a change from a translation+ rotation motion in gelatin solution to pure rotation slightly below the gel point. Both cell types show decreased motility as the gel is formed, but wild type cells maintain a motility advantage over straight rod cells in all cases.  In order to understand this advantage I have modeled the swimming of the bacteria in a pre-gel solution based on a resistive force theory². We also characterize the rotational motion by analyzing bacteria that are stuck in the gel and do not translate.   Research supported by NSF POLS.   [1] Jonathan P. Celli, Bradley S. Turner, Nezam H. Afdhal, Sarah Keates, Ionita Ghiran, Ciaran P. Kelly, Randy H. Ewoldt, Gareth H. McKinley, Peter So, Shyamsunder Erramilli, and Rama Bansil, PNAS 109, 34 (2009) [2] Guanglai Li and Jay X. Tang, Biophys. J. 88, 2726 (2006)