Figure 8.

Analysis of the growth morphologic transition that occurs during the growth of nonnative tbpD expression. Mixture model analysis of the morphology of the cellular population during growth. (A) Growth of the nonnative tbpD expression mutant as measured by optical density measured at 600 nm (OD₆₀₀) is co-plotted with the mean circularity of cells for the two components. Component 1 is associated with rod cells, component 2 is associated with spherical cells. At time point 6 there is an overall increase in circularity. (B) The fractional composition of each mixture component. The symbols are the same as those used in panel A. A reduction in circularity for component 2 during exponential growth, coupled with a concomitant decrease in component 1 circularity indicates an increase in rod-like cells in exponential growth. During the "flattening" phase, the fractional composition of the circular component 2 is near 40% of all cells but the mean circularity of this component increases dramatically indicating that a large portion of the cellular population is circular during this phase. (C) A plot of mixture model components 1 and 2 at time point 1 in the growth curve. Red lines indicate the fit curves for each component in the mixture. Green curves indicate the additive fit to the frequency distribution shown as a histogram. (D) Mixture model for time point 6, the beginning of the flattening phase. (E) Mixture model for time point 10, just before the sharp decrease in abundance of component 2. (F) Mixture model for time point 22, showing a return to rod shaped cells with a minor circular component.