Variation of the folding and dynamics of the <i><scp>E</scp>scherichia coli</i> chromosome with growth conditions

<jats:title>Summary</jats:title><jats:p>We examine whether the <jats:italic><jats:styled-content style="fixed-case">E</jats:styled-content>scherichia coli</jats:italic> chromosome is folded into a self‐adherent nucleoprotein complex, or alternately is a confined but otherwise unconstrained self‐avoiding polymer. We address this through <jats:italic>in vivo</jats:italic> visualization, using an inducible <jats:styled-content style="fixed-case"><jats:roman>GFP</jats:roman></jats:styled-content> fusion to the nucleoid‐associated protein <jats:styled-content style="fixed-case"><jats:roman>Fis</jats:roman></jats:styled-content> to non‐specifically decorate the entire chromosome. For a range of different growth conditions, the chromosome is a compact structure that does not fill the volume of the cell, and which moves from the new pole to the cell centre. During rapid growth, chromosome segregation occurs well before cell division, with daughter chromosomes coupled by a thin inter‐daughter filament before complete segregation, whereas during slow growth chromosomes stay adjacent until cell division occurs. Image correlation analysis indicates that sub‐nucleoid structure is stable on a 1 min timescale, comparable to the timescale for redistribution time measured for <jats:styled-content style="fixed-case"><jats:roman>GFP</jats:roman></jats:styled-content>–<jats:styled-content style="fixed-case"><jats:roman>Fis</jats:roman></jats:styled-content> after photobleaching. Optical deconvolution and writhe calculation analysis indicate that the nucleoid has a large‐scale coiled organization rather than being an amorphous mass. Our observations are consistent with the chromosome having a self‐adherent filament organization.</jats:p>