(354j) Intracellular Metabolism of Substrates Enhances Single-Cell Diffusion in Enterococcus Faecalis a Non-Motile Bacterium

Chemotaxis is the phenomenon in which some microorganisms are attracted or repelled by sensing chemical species in their environment. However, such behavior is not reported in non-motile microorganisms because these systems do not show a clear propulsion mechanism (e.g., flagellum rotation, surface deformation). To study the effect of chemical nutrients in the motion of these systems, we have measured the self-diffusivity of Enterococcus faecalis, a non-motile, gram-positive bacterium immersed in a phosphate buffered saline (PBS) solution containing low concentrations of a metabolizable substrate. The self-diffusivity of E. faecalis is obtained using a particle tracking software that analyzes video frames taken from samples looked at an inverted phase-contrast microscope with 100X magnification. We have shown that the diffusive behavior of E. faecalis is enhanced by the presence of dextrose, resembling observations found in synthetic systems such as the so-called catalytic nanomotors, where a chemical reaction induces autonomous motion. Surprisingly, the self-diffusivity was thirty-fold higher upon adding 2 g/L of dextrose when compared to the unamended control. The influence of dextrose on the viscosity of PBS was found to be insignificant in the range of concentrations used to conduct the experiments. In addition, a parallel study using similar-in-size inert polystyrene particles showed that the changes in diffusivity are negligible over the considered dextrose concentrations. The results support the hypothesis that the addition of an energy source to the cell suspension leads to a measurable increase in the diffusivity of the cell do to its metabolism. This study will be the corner stone for the development of a simple model for self-propulsion in bacteria by catalytic reactions.