Fig. 3. PilT–YFP localizes to the leading pole of motile cells and can dynamically re-localize within the bodies of both motile and stationary cells, providing a means to infer chemotactic behaviour.
a,b, In the majority of both stationary (a) and motile (b) cells, the PilT–YFP fusion protein localizes to one of the two cell poles (unipolar). A smaller proportion of cells have PilT–YFP localizations in both poles (bipolar) or lack appreciable localizations altogether (nonpolar). Black lines show the mean of three bio-replicates that were each conducted on different days, represented here with a different coloured circle. The data from each bio-replicate contained over n = 1,000 trajectories. c, If we consider only those motile cells that have a unipolar PilT–YFP localization, we find that PilT–YFP is significantly more likely to localize to a cell’s leading pole (mean proportion = 0.84; a two-sided binomial test of proportions rejects the null hypothesis of equal proportions with P < 1 × 10−10 for each bio-replicate, assuming that data from each cell at each time point are independent measurements). d, A time series of a motile twitching cell (cell outline shown in blue) undergoing a reversal at t = 8 min. PilT–YFP (shown in white) localizes to the leading pole, so that it swaps from one pole to the other when the cell reverses direction. e, A time series of a stationary cell reveals that PilT–YFP can swap between a cell’s two poles over time, an event we call a ‘repolarization event’. Localizations of PilT–YFP are marked with white triangles. f, A cell that is initially stationary has PilT–YFP localized to both of its poles, but subsequently PilT–YFP accumulates within its bottom pole shortly before the cell initiates movement in the downward direction. Faint dashed red lines in e and f mark the position of the two cell poles in the first image of the time series. g–i, Repolarization events can occur in cells that are initially nonpolar (g), unipolar (h) or bipolar (i). Cells shown are representative of three bio-replicates. Source data provided as a source data file.