Localization of the detected aggregates in the cells.

<p>(<i>A</i>) In each image on the time-lapse fluorescence movies, the bacterial cells are automatically isolated (each individual cell is given a unique random color). The aggregates appearing during the movie are automatically detected and their trajectory within the cell quantified (internal trajectories). (<i>B</i>) By convention, we referred to the projection of the aggregate location on the long axis of the cell as the <i>x</i>-component and that along the short axis as the <i>y</i>-component. (<i>C</i>) Histogram of the <i>x</i>-component of the initial position of the trajectories (total of 1,644 trajectories). Since the cell length at the start of the trajectory is highly variable, the <i>x</i>-component was rescaled by division by the cell half-length. After this normalization, the cell poles are located at locations −1.0 and 1.0 respectively, for every trajectory. (<i>D</i>) Experimentally measured positions of the aggregates detected in the poles (both poles pooled, <i>n</i> = 9,242 points). The green-dashed curves in (<i>D</i>–<i>F</i>) locate the 2d projection of the 3d semi-ellipsoid that was used to approximate the cell pole. (<i>E</i>) Synthetic data for bulk positions: 10,000 3d positions were drawn uniformly at random in the 3d semi-ellipsoid pole. The figure shows the corresponding 2d projections. (<i>F</i>) Synthetic data of membranary positions: 10,000 3d positions were drawn uniformly at random in the external boundary (membrane) of the 3d semi-ellipsoid pole. The figure shows the corresponding 2d projections. (<i>G</i>) To quantify figures D–F, the correlation function <i>ρ</i>(<i>s</i>) was computed as the density of positions located within crescent <i>D</i>(<i>s</i>) (gray). See text for more detail. (<i>H–I</i>) Local density of aggregate positions <i>ρ</i>(<i>s</i>) in the synthetic (<i>H</i>) and experimental (<i>I</i>) data shown in <i>E</i> (bulk, blue), <i>F</i> (membranary, red) and <i>D</i> (experimental, orange). The dashed black line shows the local density computed for 10,000 synthetic <i>2</i>d positions that were drawn uniformly at random in the 2d semi-ellipse resulting from the 2d projection of the 3d pole ellipsoid (green dashed curve in <i>D–F</i>).</p

Size-dependence of the diffusion constants.

<p>Trajectories from the LF movies (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003038#pcbi-1003038-g002" target="_blank">Fig. 2</a>) were clustered into 5 classes of increasing initial median fluorescence (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003038#pcbi-1003038-t001" target="_blank">Table 1</a>) and the corresponding MSD were averaged in each class. Symbols (open circles) show the MSD for the <i>x</i>- (<i>A</i>) and <i>y</i>-directions (<i>B</i>) for each class. Curve colors correspond to the classes from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003038#pcbi-1003038-t001" target="_blank">Table 1</a>(with median fluorescence increasing from top to bottom). The corresponding full lines show the results of the fitting procedure for each class (see text and Material and Methods). Panels (<i>C</i>) and (<i>D</i>) show the corresponding log-log plots, to explore for possible anomalous diffusion. The straight lines are linear fits over the initial regimes (first 21 seconds), before movement restriction starts saturating the MSDs. The slopes of these lines are the anomalous exponents as defined by <i>MSD</i>(<i>t</i>)∼<i>t^α</i>. Each panel indicates the average (+/− s.d.) of the exponents determined for the 4 smallest aggregates classes (thus excluding the largest class, represented by black circles). The resulting values of the diffusion constant <i>D</i> are plotted against the radius <i>r</i> in (<i>E</i>), keeping the same color code as in (A–D). Full circles indicate the values determined from fitting the MSD in the <i>x</i>-direction, while full squares show the values from the fit in the <i>y</i>-direction. The full line is a fit to a Stock-Einstein law <i>D</i>(<i>r</i>) = <i>C</i>₀/<i>r</i>, yielding <i>C₀</i> = 47.23×10³ nm³/s. The inset replots these data as a function of 1/<i>r</i>.</p

Single-aggregate tracking analysis inside <i>E. coli</i> cells.

<p>Coordinates along the <i>x</i> and <i>y</i>-axis are shown in red and black, respectively. Low frequency sampling trajectories (LF) are displayed using full lines and high frequency ones (HF) using open symbols. Light red and black swaths indicate + and −95% confidence intervals for the <i>x</i>- and <i>y</i>-axis data, respectively (for clarity, − and + intervals for the x- and y-axis data, respectively, are omitted) (<i>A</i>) Corrected mean displacement where <i>u_c</i>(<i>t</i>) is the applied correction. For the <i>y</i>-component, the correction is the time-average of the <i>y</i>-coordinate. For the <i>x</i>-component, the applied correction is cell growth : where <i>L</i>(<i>t</i>) is the cell half-length at time <i>t</i> and Δ<i>t</i> is the time interval between two consecutive images. (<i>B</i>) Corresponding mean squared displacements . The inset shows a magnification of the HF results and their close-to-linear behavior for the first 10–15 seconds (dashed line).</p