Bacterial partition complexes segregate within the volume of the nucleoid

Abstract

Precise and rapid DNA segregation is required for proper inheritance of genetic material. In most bacteria and archaea, this process is assured by a broadly conserved mitotic-like apparatus in which a NTPase (ParA) displaces the partition complex. Competing observations and models imply starkly different 3D localization patterns of the components of the partition machinery during segregation. Here we use super-resolution microscopies to localize in 3D each component of the segregation apparatus with respect to the bacterial chromosome. We show that Par proteins locate within the nucleoid volume and reveal that proper volumetric localization and segregation of partition complexes requires ATPase and DNA-binding activities of ParA. Finally, we find that the localization patterns of the different components of the partition system highly correlate with dense chromosomal regions. We propose a new mechanism in which the nucleoid provides a scaffold to guide the proper segregation of partition complexes.

Surfing on Protein Waves: Proteophoresis as a Mechanism for Bacterial Genome Partitioning

“…Other reaction-diffusion models considered the dynamics of the partition complex on the surface of the nucleoid [8][9][10][11]. Recent experiments, however, demonstrate that partition complexes and ParA translocate through the interior of the nucleoid, not at its surface [5].Recently, in the context of the active colloids literature, there have been attempts to describe the ParABS system using models inspired by the diffusiophoresis [16,17] of active colloidal particles in solute concentration gradients [2,18]. These works have several important limitations for applications to ParABS, such as: rigid spherical particles (with surface reactions only), the steady-state approximation, only one ParA population, or reproducing equilibrium positioning only.…”

“…Other reaction-diffusion models considered the dynamics of the partition complex on the surface of the nucleoid [8][9][10][11]. Recent experiments, however, demonstrate that partition complexes and ParA translocate through the interior of the nucleoid, not at its surface [5].…”

“…Our work is fully inspired by studies of one of the most widespread and ancient mechanisms of liquid phase macromolecular segregation and positioning known in nature: bacterial DNA segregation systems. Despite the fundamental importance of these systems in the bacterial world and intensive experimental studies extending over 30-years [3][4][5], no global picture encompasses fully the experimental observations. Partition systems encode only three elements that are necessary and sufficient for active partitioning: two proteins ParA and ParB, and a specific sequence parS encoded on DNA.…”

“…Recent superresolution microscopy experiments have been unable to observe filamentous structures of ParA [5,13], disfavoring polymerization-based models [12]. Reaction-diffusion models have been mainly investigated numerically to describe experimental observations like single or multiple ParBS complex positioning.…”

“…The pool of ParB proteins is recruited as a cluster of spherical shape centered around the sequence parS, forming the ParBS partition complex [4]. These ParBS cargos interact with ParA bound onto chromosomal DNA (ParA-slow) [6,7], triggering unbinding of ParA by inducing conformational changes through stimulation of adenosine triphosphate (ATP) hydrolysis and/or direct ParB-ParA contact [8], and thereby allowing ParA diffusion in the cytoplasm (ParA-fast) [5]. This process entails the oscillation of ParA from pole to pole and the separation of the ParBS partition complex into two complexes with distinct sub-cellular trajectories and long-term localization.…”