Shewanella Oneidensis MR-1 Population-Level Chemotaxis In a Diffusion Gradient Chamber

Shewanella species are famous for their broad range of terminal electron acceptors, nearly ubiquitous presence in various environmental niches, and the ability to perform chemotaxis towards both organic and inorganic electron acceptors. Knowledge of Shewanella’s chemotactic properties is important to understand its competitiveness and roles in elemental cycling and bioremediation (e.g., precipitation of soluble uranium oxides). Population-level microbial chemotaxis involves a complex interplay of cellular process (growth, metabolism, chemotaxis, and random motility) and molecular processes (diffusion of electron donors and acceptors that serve as chemoattractants). This paper describes use of a diffusion gradient chamber (DGC) to study population-level growth and chemotaxis of Shewanella oneidensis MR-1 in response to applied and cell-generated gradients of chemotactic electron acceptors. A mathematical model describing the key cellular and molecular processes governing S. oneidensis’ chemotaxis was developed and used to analyze the experimental results.  Population-level chemotactic responses of wild-type S. oneidensis MR-1 and electron-acceptor reductase mutants to uniformly distributed electron acceptors, pre-established unsteady or quasi-steady state gradient of electron acceptors were explored in the DGC. The model was able to reproduce key trends in the observed cell growth and migration patterns.  The predicted velocities of chemotactic cell bands closely matched those measured in the DGC. These results validate the use of the DGC and its mathematical model to measure and simulate Shewanella’s chemotaxis in response to electron acceptor gradients.