Fig. 1: The microfluidic signal generator (MSG) creates automated, precise high-frequency fluctuations in nutrient concentration while enabling single-cell microscopy.
From: A distinct growth physiology enhances bacterial growth under rapid nutrient fluctuations
a The two channel configurations: the MSG switches between two media (top) and the straight channels each steadily deliver a single medium (bottom). Each experiment contains four parallel channels: one MSG and three straight. The two MSG channels displayed here schematically represent the flow conditions that deliver either Clow or Chigh to the cells. The upstream portion of the MSG switches the nutrient media delivered to cells via automated control over the pressure differences driving each medium while maintaining a constant flow rate into the device. The top MSG delivers Chigh (red) to cells by pressurizing the red inlet higher than the Clow (purple) inlet. The wider downstream section fits over ten imaging fields of view at ×60 magnification. b Bacteria were exposed to fluctuating signals in the form of even oscillations between a low and a high LB concentration (Clow and Chigh), with periods, T, between 30 s and 60 min. Three control environments, Clow, Cave, and Chigh, were run simultaneously with each fluctuating environment. c Fluorescence intensity, from fluorescein added to one of the media, illustrates the signal received at the cell imaging region over multiple oscillations (T = 30 s). Transitions between media are completed in <3 s. d Individual E. coli cells growing within the MSG. Cells were imaged at 117 s intervals; timestamps of selected images are displayed in minutes. Cells divide between t2 and t3 (orange) and between t4 and t5 (blue), and can be seen elongating between other frames. One of the two cells emerging from division is swept away with the flow. Images were cropped from one steady nutrient experiment and are representative of the growth behaviors observed in all experiments described in this paper.
