Extended Data Fig. 4: A temporal increase in succinate concentration does not induce a chemotactic response in surface-attached P. aeruginosa.
(a, b) Using the approach outlined in Fig. 2, cells were exposed to temporal increases in succinate concentration (CMIN = 0.84 mM, CMAX = 1.16 mM; blue line). This generates mean temporal concentration gradients approximating the gradient experienced by cells moving towards increasing succinate concentrations in the dual-inlet chemotaxis experiments (Extended Data Fig. 1), but with 16,000-fold smaller spatial gradients. If cells can sense these temporal stimuli, the temporal increase in succinate concentration would be predicted to suppress reversals. (c) In the 1 h period before the succinate gradient entered the microfluidic device (interval t1) cell reversal rates were statistically indistinguishable between experiment (white bar, blue outline) and control (white bar, green outline; one-sided exact Poisson test (Methods) yielded p = 0. 762). Similarly, the reversal rates in the presence of a temporal succinate gradient (interval t2; light grey bar, blue outline) and in the 1 h period after the gradient had cleared the microfluidic device (interval t3; dark grey bar, blue outline) were statistically indistinguishable from the reversal rates during the same time periods in the control (p = 0.342 and p = 0.872). The number of reversals observed was nr = 2709 and 2980 across nt = 636,364 and 709,607 trajectory points in the control and experimental conditions respectively. Error bars show 95% confidence intervals about the estimated reversal rates assuming that reversals follow a Poisson distribution (Methods). (d, e, f) A second bio-replicate confirmed that when comparing between experiment and control, reversal rates were indistinguishable during time periods t1 (white bars, p ≈ 1), t2 (light gray bars, p = 0.077) and t3 (dark gray bars, p = 0.468). p-values were obtained from a one-sided exact Poisson test (Methods); nr = 2101 and 2034 across nt = 536,892 and 504,264 trajectory points in the control and experimental conditions respectively. Error bars show 95% confidence intervals about the mean reversal rates, assuming that reversals follow a Poisson distribution (Methods). Source data provided as a Source Data file.
