The physical nature of the bacterial chromosome has important implications for its function. Using high-resolution dynamic tracking, we observe the existence of rare but ubiquitous 'rapid movements' of chromosomal loci exhibiting near-ballistic dynamics. This suggests that these movements are either driven by an active machinery or part of stress-relaxation mechanisms. Comparison with a null physical model for subdiffusive chromosomal dynamics shows that rapid movements are excursions from a basal subdiffusive dynamics, likely due to driven and/or stress-relaxation motion. Additionally, rapid movements are in some cases coupled with known transitions of chromosomal segregation. They do not co-occur strictly with replication, their frequency varies with growth condition and chromosomal coordinate, and they show a preference for longitudinal motion. These findings support an emerging picture of the bacterial chromosome as off-equilibrium active matter and help developing a correct physical model of its in vivo dynamic structure.
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We acknowledge useful discussions with Olivier Espeli, Bianca Sclavi, Vittore Scolari, Francois-Xavier Barre, Cristophe Possoz, Frederic Boccard, Camille Cibot, Michele Valens and Paolo Pierobon. This work was supported by the International Human Frontier Science Program Organization, grant RGY0069/2009-C, and Consejo Nacional de Ciencia y Tecnologia (CONACYT).