Fig. 4: Single-cell analysis of a semi-lethal pulse.

A Schematic diagram illustrating a microfluidic experiment exposing MG:GT and MG/pBGT populations to a semi-lethal antibiotic pulse. B Results obtained after tracking individual cell lineages in time-lapse movies. Cell lineages are classified based on whether they survived treatment (orange and blue) or if they died during drug exposure. C GFP distributions of cells in MG:GT (left) and MG/pBGT (right) show significant differences in mean GFP and variance. For MG:GT, the fluorescent distribution is characterized by low variance and no significant differences in mean GFP between cells that produced filaments and were killed (light orange) or survived (light blue), as well as for cells that did not produce filaments and died (dark orange), and those that survived drug exposure (dark blue). The plasmid-bearing population exhibits a large variance in GFP distribution, with survived cells showing an increased mean fluorescence relative to cells killed. For surviving cells, mean GFP was significantly lower for cells that did not produce filaments than cells that filamented. D Histogram shows the number of division events per cell lineage in the MG/pBGT (right) and MG:GT (left) populations prior to drug exposure. E Fraction of cells alive as a function of time for lineages present upon antibiotic introduction. The y-axis denotes the initial fluorescence of cells in each initial GFP bin, and each box represents the proportion of cells that are still alive in each time step (high survival rates in a light color). F Histogram of GFP expression for MG/pBGT cells estimated after drug exposure. The size of each bar represents the probability of survival estimated for each GFP level after exposure to a semi-lethal pulse of AMP. Note how the distribution appears bimodal, with high survival rates at intermediate and very high fluorescent intensities. G Diagram illustrating that this bimodal distribution results from a stress response mechanism producing filamented cells and provides transient resistance to ampicillin in cells with intermediate fluorescent values. Cells with low GFP values before drug exposure have a low probability of survival, while cells with high fluorescent intensities are highly resistant to the antibiotic.