Analysis of chemotactic cell motility of <i>secG⁻</i> cells.

Time-lapse image series were captured and stored on a computer hard drive at 30-second intervals. Images were taken at magnifications of 10X and 40X every 6 s. The DIAS software was used to trace individual cells along image series and calculate motility parameters. Objects whose speed was <2 µm/min were excluded from the analysis. Speed refers to the speed of the cell's centroid movement along the total path; directionality indicates migration straightness; direction change refers to the number and frequency of turns; persistence is an estimation of movement in the direction of the path; and roundness indicates the cell polarity. Values are mean ± standard deviation of >30 cells from three or more independent experiments. The difference in speed was statistically significant (P value 0.0416* and 0.012**).