Fig. 8
Negative control to examine signals solely from the activities of motile bacteria. (a) Averaged differential spectrograms showing the effects of four different conditions on the fluctuation spectra of DLD microclusters. The top left panel shows fresh targets treated with PBS applied after the baseline time of 4 hours; top right panel shows formalin washed targets treated with PBS solution; bottom left panel shows formalin-washed targets infected with 1000 cfu/mL; bottom right panel shows fresh target infected with 1000 cfu/mL of salmonella. The 4 hour mark is indicated by the black horizontal line. Measurements before the 4 hours mark establish the baseline spectrum for each sample, which is used to compensate for the extrinsic variability between samples. The color scale on each plot visualizes the relative change in the spectral weight with respect to the baseline. The contour lines are set at 0.2 unit interval of \(\Delta \log (S)\). Each panel is the average over N replicates, where N is the number as noted on each panel. (b) Normalized spectral density difference of microclusters infected with S. enterica compared to PBS treatment, over three different frequency bands. Translucent bands and the bars show standard error for the spectral density shifts. Dotted black line shows the growth curve for the concentration of S. enterica over the same period of time, starting from 1 kcfu/mL. The details of how the concentration curve was obtained and calibrated can be found in the Information S3.
