Swimming characterization of Serratia marcescens for bio-hybrid micro-robotics

The last decade has seen remarkable growth in the development of bio-hybrid micron-scale systems, which combine bacteria, tissue, and other biological material with synthetic components to produce uniquely capable devices. Serratia marcescens, a gram-negative bacteria, has many characteristics useful for bio-hybrid systems, including natural adhesiveness, high motility, and ease of cultivation. In light of the utility of the bacterium S. marcescens as a component of bio-hybrid microsystems, we characterize the motility of the species in a fashion useful for those developing such microdevices. The species also provides a complementary platform for studying attributes of flagellated bacteria motility which have thus far been primarily discussed in Escherichia coli. Using a three-dimensional multi-bacteria single-camera tracking system, we capture the trajectories of individual bacteria and calculate run speeds and tumble rates. The mean speed and tumble rate at room temperature are found to be 26 mu m/s and 1.34 +/- 0.16 tumbles/s, respectively. We characterize the relationship between motility and position on a growth plate and examine the effect of viscosity and temperature on bacterial motion. A linear relationship is found between speed and temperature proportional to that seen previously with E. coli. We also quantify the response of S. marcescens to the chemoattractant L-aspartate, with the strongest chemotactic response at a gradient of 10(-4) M/mm. Finally, population scale measurements are compared to individual bacterial dynamics in a linear gradient and are used to validate a simple model of bacterial population dynamics under chemotaxis.