Physics of Motility of Bacteria Living in Mucus Gels

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The focus of the proposed research is to understand the fundamental physics of bacterial motility in a non-Newtonian, viscoelastic gel and to correlate the motility with the viscoelastic properties of the medium. Using the ulcer causing bacterium H. pylori in mucin gels we will explore two regimes of motion: translational motion in solutions at neutral pH, and pure rotation without translation in gels at low pH. We will apply state-of-the-art imaging techniques such as two-photon microscopy and single and multi-particle tracking for quantitative measurements of the dynamics of the motion of the bacterium and its impact on the local micro-rheology of its environment. Global or bulk changes in the mechanical and rheological properties of the bacteria infected gel will be determined by oscillatory shear rheology. Comparative studies of the wild-type H. pylori bacteria with mutants deficient in specific receptors or flagella, as well as with different body shapes, will enable us to assess the effect of the many variables at play in this complex living system. The experimental studies will be complemented by computational analysis and theoretical modeling of bacterial motility and flagella dynamics in gels to provide quantitative estimates of the velocity, forces, and torques involved in the motion and understand the underlying physics of how the motion correlates with the viscoelasticity. The results have potential relevance to many biomedical applications where motility in a gel plays a key role, such as in the infection of stomach mucus by H. pylori which leads to ulcers and cancer, to culturing of bacteria and cells in 3-dimensional gel matrices, in the design of bacterial resistant hydrogels for artificial tissues, and in the development of nano- and microscale swimmers and rotators. The research project, involving collaborators with expertise in theoretical physics, biomedical imaging, microbiology, and gastroenterology, will provide a unique opportunity for multidisciplinary training of graduate and undergraduate students in the areas of biophysics, fluid dynamics and microbiology, biochemistry and molecular biology. Videos on bacterial motility and simple analysis tools will be developed for use in undergraduate courses and for demonstration purposes. We will take advantage of the diversity of our team, and the broad appeal of the research topic, to do outreach activities involving presentations to a broader audience, including local high schools, and minority and other community groups and to recruit women and minority undergraduate and high school students to participate in the research.