Microfluidic Analysis of Thermotaxis in Escherichia Coli
Maeda et al. (1976) observed that Escherichia coli sense the direction of a temperature gradient, performing thermotaxis (directional motion in a temperature gradient) and aggregating at a preferred temperature. The molecular details of bacterial thermotaxis are still poorly understood. We have developed a microfluidic setup to measure thermotaxis of swimming bacteria in a dilute suspension at high-throughput. Extensive data on thermotactic migration of a given bacterial strain in a stable thermal gradient can be collected in less than 30 minutes. The microfluidic device is made of polydimethylsiloxane (PDMS) and has a 16 mm long, 500 μm wide and 40 μm deep test channel across which a linear, programmable temperature gradient is formed. A bacterial suspension is perfused through the channel at a low speed, such that individual cells have sufficient time to explore the gradient before they are imaged near the channel exit. We have developed imaging software to identify healthy swimming cells and determine their trajectories for taxis analysis. The spatial distribution of the bacterial trajectories is used as a measure of their taxis performance, and we show that the taxis performance is correlated with the steepness of the temperature gradient. Inversion of the thermal response can be induced by chemical adaptation to aspartate and serine, but adaptation to aspartate or serine only give a very weak inversion or null response, respectively.Maeda, K., Imae, Y., Shioi, J.I., Oosawa, F. (1976). J. Bacteriol. 127:1039–1046.