Gene loci fluctuations reveal bacterial chromosome dynamical organization

Chromosomal sites in rod-like bacteria move sub-diffusely, driven by the out-of-equilibrium nature of the viscoelastic, crowded intracellular environment. Furthermore, it has been shown that there is a pronounced dynamical asymmetry between longitudinal (long-axis) and transverse (radial) motions, manifested in different exponents in the mean-square displacements <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>M</mml:mi> <mml:mi>S</mml:mi> <mml:mi>D</mml:mi> <mml:mfenced><mml:mrow><mml:mi>t</mml:mi></mml:mrow> </mml:mfenced> <mml:mo>~</mml:mo> <mml:msup><mml:mrow><mml:mi>t</mml:mi></mml:mrow> <mml:mrow><mml:mi>α</mml:mi></mml:mrow> </mml:msup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow> <mml:mrow><mml:mi>l</mml:mi></mml:mrow> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow> <mml:mrow><mml:mi>r</mml:mi></mml:mrow> </mml:msub> </mml:math> respectively. Here, using polymer simulations and experimental observations of a locus in Bacillus subtilis, we substantiate the notion that asymmetric dynamics are a result of the asymmetric structure of the bacterial chromosome modeled as a bottlebrush polymer in a poor solvent. Our simulations recapitulate the observed asymmetry as well as the range of the observed exponent values that are related to scaling models of polymer dynamics, lending support to the notion that asymmetric dynamics is a consequence of the bottlebrush structure of the bacterial chromosome.