Dynamic bridging explains sub-diffusive movement of chromosomal loci

Chromosomal loci in bacterial cells show a robust sub-diffusive scaling of the mean square displacement (MSD)~ τ^0.4 under various growth conditions and antibiotic treatments. Recent experiments have also shown that DNA-bridging Nucleoid Associated Proteins (NAPs) play an important role in chromosome organization and compaction. Here, using polymer simulations we investigate the role of DNA bridging in determining the dynamics of chromosomal loci. We find that bridging compacts the polymer and reproduces the sub-diffusive dynamics of monomers at timescales shorter than the bridge lifetime. Furthermore, the measured scaling exponent defines a relationship between chromosome compaction and bridge lifetime. Based on the observed mobility of chromosomal loci, we predict a lower bound on the average bridge lifetime of ~ 9 seconds. Finally, we show how bridging influences the average mesh size of the polymer, an experimentally measurable quantity.