(A) A schematic of the Mother Machine microfluidic experiment. Cells are loaded into growth channels that are capped on one end and surrounded by flowing media. A ‘mother’ cell settles at the capped end, and produces daughters. The daughters at the uncapped end of the growth channel are washed away by the current of media. Positions were filmed for up to 4 days, and for visualization purposes the images from each growth channel were cropped and aligned to generate a kymograph depicting time on the x-axis. (B) Filmstrip kymographs from representative mother-machine experiments using conditioned media at OD600 0.8 and sucC reporter strain (left panel) or conditioned media at OD600 2.0 using alsS reporter strain (right panel). Dashed red lines show the trend of growth of two daughters, a sucC+ and sucC- pair on the left panel and a alsS+ and alsS- pair on the right panel. As seen from the slope of the trend lines and as indicated below the kymographs, the elongation rates of both sucC+ and alsS+ cells are slower than their counterparts. All values reported (events per 100 hr, elongation rate, and dwell time) were averaged from at least three separate movies per condition. Representative mother machine movies are available in the supplement. (C) Extracellular acetate levels activate heterogeneous expression of the alsS promoter. A histogram shows the population of cells expressing different levels of YFP under control of the alsS promoter. When no acetate is added (green line), practically all cells are in the low expressing portion of the histogram. When extracellular acetate levels are added to mimic the maximal amount produced in the growth curve (orange and red lines), some cells remain in the low expressing portion of the histogram, but a correspondingly larger number of cells are in the long tail of high alsS expression.