Raw data used for plots in this study.

Escherichia coli is arguably one of the most studied bacterial model systems in modern biology. While E. coli are normally rod-shaped gram-negative bacteria, they are known to undergo conditional morphology changes under environmental and nutrient stress. In this study, using an infection-based in-vitro infection model system combined with advanced dynamical imaging, we present the first molecular details of uropathogenic E. coli (UPEC) dividing to form and proliferate as coccoid-shaped cells inside human host cells. For these intracellular UPEC cells, the frequency of cell division outpaced the rate of cell growth, resulting in a morphological transition from traditional rod-shape to coccobacilli. We also visualized the subcellular protein dynamics in these cells and noted that the division proteins follow the similar localization and constriction patterns that have been demonstrated for vegetative growth. However, unlike for fast-growing rod-shaped cells, FtsZ constriction in intracellular UPEC occurs prior to visual nucleoid segregation. Our results suggest that the modulation of division rate contributes to morphological adaptability of intracellular UPEC at the single-cell level.