Additions and corrections

Bacterial nucleoid structure probed by active drag and resistive pulse sensing

Vivek V. Thacker, Krystyna Bromek, Benoit Meijer, Jurij Kotar, Bianca Sclavi, Marco Cosentino Lagomarsino, Ulrich F. Keyser and Pietro Cicuta

Integr. Biol., 2014, (DOI: 10.1039/C3IB40147B ). Amendment published 24th January 2014.

The image for Figure 1 and 3 is incomplete. Please find below the corrected figure.

Fig. 1 An overview of the experimental techniques. (a) Representative fluorescence images of the nucleoids stained with DAPI (left) illustrate the large differences in the structure of WT and Dhns nucleoids qualitatively. Lightly stained areas correspond to lower DNA densities within the nucleoid. Nucleoids were obtained from the E. coli populations at the late exponential, early stationary and stationary growth phases as indicated on the growthcurve (right). (b) Resistive pulse sensing of nucleoids: the reservoirs are filled with buffer and an excess pressure is applied to the reservoir on the right which drives the nucleoids through the microcapillary. (c) Drag measurements using optical tweezers: the laser trap is driven along a sinusoidal path with an amplitude of 3.1 mm. The force induced by the trap on the nucleoid (purple arrow) is proportional to the nucleoid displacement from the center of the trap and is balanced at all times by the hydrodynamic drag.

Fig. 3 Fig. 3 The hydrodynamic radius of nucleoids can be measured directly with optical tweezers. (a) Individual nucleoids are subjected to a harmonic force (arrows) in the optical trap. The composite of selected frames recorded in the experiment shows the nucleoid advancing along a sinusoidal path, following that of the optical tweezers (red curve, shown with exaggerated phase shift ΔΦ).Measurements of the positions of the nucleoid are synchronized with the trap positions, allowing ΔΦ to be obtained. (b) Power spectral density of the motion of a nucleoid at two driving frequencies as indicated in the legend. The peak in each spectrum corresponds exactly to the driving frequency. (c) Phase shifts are plotted as a function of the angular frequency for typically 5 nucleoids each from WT (upper panel) and Δhns (lower panel) strains at different stages of growth. Color scheme follows that of Fig. 2.

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