Membraneless organelles formed by liquid-liquid phase separation increase bacterial fitness

TL;DR

This study reveals that bacteria form liquid-like aggresomes via phase separation, which enhances their ability to withstand environmental stresses, expanding understanding of bacterial cell organization.

Contribution

It demonstrates that bacterial aggresomes are liquid-like structures formed by phase separation, a phenomenon previously mainly associated with eukaryotic cells.

Findings

Aggresomes are dynamic, liquid-like protein assemblies in bacteria.

Formation of aggresomes increases bacterial stress tolerance.

Aggresomes are present across multiple bacterial species.

Abstract

Liquid-liquid phase separation is emerging as a crucial phenomenon in several fundamental cell processes. A range of eukaryotic systems exhibit liquid condensates. However, their function in bacteria, which in general lack membrane-bound compartments, remains less clear. Here, we used high-resolution optical microscopy to observe single bacterial aggresomes, nanostructured intracellular assemblies of proteins, to undercover their role in cell stress. We find that proteins inside aggresomes are mobile and undergo dynamic turnover, consistent with a liquid state. Our observations are in quantitative agreement with phase-separated liquid droplet formation driven by interacting proteins under thermal equilibrium that nucleate following diffusive collisions in the cytoplasm. We have discovered aggresomes in multiple species of bacteria, and show that these emergent, metastable liquid-structured protein assemblies increase bacterial fitness by enabling cells to tolerate environmental stresses.