(815a) Physical Modeling of Chromosome Segregation in E. Coli Reveals Impact of Force and DNA Relaxation

The physical mechanism by which Escherichia coli segregates its chromosomes for partitioning into daughter cells is unknown. In several other species of bacteria, the action of a segregation force is responsible for pulling the newly replicated chromosomes apart from the nascent strand. This suggests that such a force may play a role in E. coli chromosome segregation. In our previous work, we developed a Rouse polymer model in a viscoelastic medium that accurately describes the equilibrium motion of a chromosomal locus. In this work, we extend our model to examine the effects of a segregation force acting on a single monomer on the polymer dynamic behavior. We then compare our predictions for the mean displacement and velocity autocorrelation to the motion of fluorescently labeled oriC loci in E. coli during segregation. The oriC locus is the origin of replication and is among the first regions to have copies moved to opposite sides of the cell. The mean displacement scales as a power law in time as t^𝜶, where 𝜶≈0.3-0.4, and shows a positive velocity autocorrelation. Our model predicts that the mean displacement of an oriC locus scales as t^0.35, and that the motion has a positive velocity autocorrelation due to the action of the segregation force. Thus, the motion of the oriC locus is consistent with the action of a segregation force, though the source of this force is still a mystery.