Stirring by microrganisms: the case of Shewanella

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The motion of microorganisms introduces flows in their environment that affect the dispersal of nutrients and other solutes. The flows can be visualized and measured by the tracking of passively advected particles, which in the case of Escherichia coli and the marine alga Chlamydomonas reinhardtii has revealed that the spreading process does not follow the laws of normal diffusion: the probability density functions are not Gaussian, and the spreading law can change from a normal diffusive law to a super-diffusive law. We here propose to explore this behaviour further in a combination of experimental studies on Shewanella and theoretical modeling of the dispersion. Different strains of Shewanella show variations in the swimming speed, the statistics of their reversals as well as the length and number of their flagella. These properties enter computational models that will be used to simulate the spreading process, and theoretical descriptions that will be based on continuous time random walks. We plan to study communities of varying densities and mixtures of different strains, as well as the motion in constrained flat cells and wedges, for an in-depth characterization of Shewanellas motility and chemotactic response in various environments.