In bacteria, chromosomal architecture shows strong spatial and temporal organization, and regulates key cellular functions, such as transcription. Tracking the motion of chromosomal loci at short timescales provides information related to both the physical state of the nucleo-protein complex and its local environment, independent of large-scale motions related to genome segregation. Here we investigate the short-time (0.1-10 s) dynamics of fluorescently labelled chromosomal loci in Escherichia coli at different growth rates. At these timescales, we observe for the first time a dependence of the loci's apparent diffusion on both their subcellular localization and chromosomal coordinate, and we provide evidence that the properties of the chromosome are similar in the tested growth conditions. Our results indicate that either non-equilibrium fluctuations due to enzyme activity or the organization of the genome as a polymer-protein complex vary as a function of the distance from the origin of replication.
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We are very grateful to V.G. Benza, B. Sclavi, A. Spakowitz, O. Espeli, P.A. Wiggins, N. Kleckner, L. Mirny and G. Fraser for helpful discussions, and to V.G. Benza for revision of this manuscript. We thank J. Kotar and C. Saggioro for their help with the experimental setups and bacterial strains, and O. Espeli and F. Boccard for the gift of bacterial strains developed in their laboratory. This work was supported by the International Human Frontier Science Program Organization, grant RGY0069/2009-C, the EU ITN-Transpol, Royal Society International Joint Project and Consejo Nacional de Ciencia y Tecnologia (CONACYT).