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

TLDR

Liquid‑liquid phase separation is a key phenomenon in many cellular processes, yet its role in bacteria—organisms that typically lack membrane‑bound compartments—is still unclear. The study employed high‑resolution optical microscopy to observe single bacterial aggresomes and investigate their role in cellular stress. The authors found that bacterial aggresomes behave as dynamic liquid droplets, with mobile proteins and turnover consistent with phase‑separated condensates, and that these structures, present across multiple species, enhance bacterial fitness by improving tolerance to environmental stresses.

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 found 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.