The bacterial nucleoid: nature, dynamics and sister segregation

Abstract

Recent studies reveal that the bacterial nucleoid has a defined, self-adherent shape and an underlying longitudinal organization and comprises a viscoelastic matrix. Within this shape, mobility is enhanced by ATP-dependent processes and individual loci can undergo ballistic off-equilibrium movements. In E.coli, two global dynamic nucleoid behaviors emerge pointing to nucleoid-wide accumulation and relief of internal stress. Sister segregation begins with local splitting of individual loci, which is delayed at origin, terminus and specialized interstitial snap regions. Globally, as studied in several systems, segregation is a multi-step process in which internal nucleoid state plays critical roles that involve both compaction and expansion. The origin and terminus regions undergo specialized programs partially driven by complex ATP burning mechanisms such as a ParAB Brownian ratchet and a septum-associated FtsK motor. These recent findings reveal strong, direct parallels among events in different systems and between bacterial nucleoids and mammalian chromosomes with respect to physical properties, internal organization and dynamic behaviors.

Rapid pairing and resegregation of distant homologous loci enables double-strand break repair in bacteria

“…3). Such a process may be similar to the movement seen during chromosome segregation in E. coli (Fisher et al, 2013;Kleckner et al, 2014). During DNA replication in E. coli, recently duplicated sections of the chromosome remain transiently cohesed together; elimination of the cohesion, including resolution of precatenanes by topoisomerase IV, then allows the rapid movement of sister loci to opposite sides of the cell.…”

“…During DNA replication in E. coli, recently duplicated sections of the chromosome remain transiently cohesed together; elimination of the cohesion, including resolution of precatenanes by topoisomerase IV, then allows the rapid movement of sister loci to opposite sides of the cell. This movement is likely not driven by a dedicated protein or protein complex but instead may represent a sort of stress relaxation mechanism (Joshi et al, 2011;Fisher et al, 2013;Kleckner et al, 2014). We envision a similar mechanism driving the resegregation of sister loci after DSB repair.…”

Condensin- and Replication-Mediated Bacterial Chromosome Folding and Origin Condensation Revealed by Hi-C and Super-resolution Imaging

“…This interplay is especially acute in bacteria, which lack the well-characterized segregation apparatus of eukaryotes. Several mechanisms have been suggested to promote sister segregation, such as passive disentangling thanks to tethering to the cell envelope, active segregation by partition complexes, or mechanical ''stress'' relief models (Kleckner et al, 2014).…”

Species-specific supercoil dynamics of the bacterial nucleoid

“…Progress in understanding the structure/function mechanics of the bacterial chromosome greatly improved with development of techniques that allow real time visualization of bacterial nucleoids inside living cells and the ability to follow specific chromosomal loci using fluorescent labels (Kleckner et al 2014;Wang et al 2008). Nucleoids are self-adherent filaments stochastically organized locally into approximately 10-kb domains in growing cells (Cunha et al 2005;Espeli et al 2008;Hadizadeh Yazdi et al 2012;Postow et al 2004;Stein et al 2005;Wiggins et al 2010).…”