The fraction of motile bacteria in a culture of Escherichia coli and its evolution along the growth curve

Although the population growth kinetics of Escherichia coli are extensively documented, the quantitative and detailed characterization of motility evolution and cell morphology across distinct culture phases remains unavailable, despite its potential impact on active matter studies. In this work, we analyze the temporal evolution of bacterial activity and aspect ratio, demonstrating that motility distribution is not constant. A key finding is the existence of a non-negligible fraction of non-motile bacteria, the proportion of which varies depending on the growth stage of the population. This demographic evolution of the active and inactive fractions and the cell aspect ratio can have direct implications for collective behavior of bacterial suspensions.