Fig. 4: Tar and Tsr occupancy in arrays.

Receptor occupancy, defined as the receptor-to-CheA ratio, reflects the fraction of potential array positions occupied by either Tar or Tsr receptors. To assess occupancy, we used cells in which either Tsr (strain MK27) or Tar (strain MK30) was tagged with mScarlet, in addition to CheA::CheY–mYFP. a Upper plots: Distributions of array sizes (mYFP fluorescence) for both strains in exponential and stationary growth phases, as indicated. Lower plots: Corresponding distributions of receptor levels in each array (mScarlet fluorescence). b Distributions of the mScarlet-to-mYFP fluorescence intensity ratio in individual arrays, representing either Tsr-to-CheA (blue) or Tar-to-CheA (red) ratios. Data are shown for cells in exponential (upper plot) and stationary (lower plot) growth phases. Means are indicated by bars. c Upper plots: Growth of individual arrays (left; mYFP fluorescence) and the corresponding changes in Tar occupancy within those arrays (right; red/yellow fluorescence) following a shift from stationary to exponential phase, recorded by placing stationary-phase cells onto an agarose hydrogel pad with fresh growth medium. Sample images are shown (lower-right panel), with the arrow highlighting the same array over time. Lower plot: Additional traces of Tar occupancy in individual arrays, showing an overall shift (red bars) consistent with the population-level data in (b). Different symbol colors correspond to different arrays. Fluorescence intensity was corrected for bleaching (see Fig. S3).