ATP-driven separation of liquid phase condensates in bacteria

TL;DR

This study reveals an active mechanism in bacteria that organizes liquid phase condensates, involving specific proteins and motor activity, crucial for DNA segregation and cellular organization.

Contribution

It uncovers a novel active process that splits, segregates, and localizes LLPS condensates in bacterial cells, highlighting the role of ParA motor in this organization.

Findings

ParB forms nanometer-sized condensates associated with parS.

ParB molecules diffuse rapidly but are confined within condensates.

ParA motor prevents fusion of ParB condensates.

Abstract

Liquid-liquid phase separated (LLPS) states are key to compartmentalise components in the absence of membranes, however it is unclear whether LLPS condensates are actively and specifically organized in the sub-cellular space and by which mechanisms. Here, we address this question by focusing on the ParABS DNA segregation system, composed of a centromeric-like sequence (parS), a DNA-binding protein (ParB) and a motor (ParA). We show that parS-ParB associate to form nanometer-sized, round condensates. ParB molecules diffuse rapidly within the nucleoid volume, but display confined motions when trapped inside ParB condensates. Single ParB molecules are able to rapidly diffuse between different condensates, and nucleation is strongly favoured by parS. Notably, the ParA motor is required to prevent the fusion of ParB condensates. These results describe a novel active mechanism that splits, segregates and localises non-canonical LLPS condensates in the sub-cellular space.