Species and Scale Dependence of Bacterial Motion Dynamics

Accurate models of bacterial motion dynamics are important in several applications, including development of improved predictive tools for bioremediation. While many bioremediation models neglect the motility of the bacteria, others have treated motility using an advection dispersion equation (ADE), which assumes that the motion of the bacteria is Brownian. The assumption of Brownian motion to describe motility has enormous implications on predictive capabilities of bioremediation models, yet experimental evidence of this assumption is mixed^[1][2][3]. We hypothesize that this is due to the species and scale dependence of the motion dynamics.

We test our hypothesis by analyzing videos of motile bacteria of different species in open domains. Trajectories of individual cells ranging from several seconds to few minutes in duration are extracted in neutral conditions (in the absence of any chemical or redox gradient). The density of the bacteria is kept low so that the interaction between individual cells is minimal. Certain species of bacteria exhibit a transition from Fickian (Brownian) to non-Fickian behavior whereas others continue to exhibit non-Fickian behavior. We plan to identify the effect of environmental conditions (e.g. presence of obstacles, chemical or redox gradient, and flow) on the timescales where these transitions occur. For species of motile bacteria considered in this research, the analysis helps in determining the suitability of ADE based transport models as a function of timescale and environmental conditions, and provides pathway for development of methodologies to include bacterial motion dynamics in bioremediation implementations.

Figure: Video frames of motile bacteria with the last 10 seconds of their trajectories drawn in red. (left) Pelosinus and (right) Geobacter.

[1] Ariel, Gil, et al. "Swarming bacteria migrate by Lévy Walk." Nature Communications 6 (2015).

[2] Saragosti, Jonathan, Pascal Silberzan, and Axel Buguin. "Modeling E. coli tumbles by rotational diffusion. Implications for chemotaxis." PloS one 7.4 (2012): e35412.

[3] Wu, Mingming, et al. "Collective bacterial dynamics revealed using a three-dimensional population-scale defocused particle tracking technique." Applied and Environmental Microbiology 72.7 (2006): 4987-4994.