Aggresomes protect mRNA under stress in Escherichia coli

Membraneless droplets formed through liquid-liquid phase separation of ribonucleoprotein particles contribute to mRNA storage in eukaryotic cells. How such aggresomes contribute to mRNA dynamics under stress and their functional role are less understood in bacteria. Here we used multiple approaches including live-cell imaging, polymer physics modelling and transcriptomics to show that prolonged stress leading to ATP depletion in Escherichia coli results in increased aggresome formation, compaction and selective mRNA enrichment within these aggresomes. Longer transcripts accumulate more in aggresomes than in the cytosol. Mass spectrometry and mutagenesis studies showed that mRNA ribonucleases are excluded from aggresomes due to electrostatic repulsion arising from their negative surface charges. Experiments with fluorescent reporters and disruption of aggresome formation showed that mRNA storage within aggresomes promoted rapid translation reactivation and is associated with reduced lag phases during growth after stress removal. Our findings suggest that mRNA storage within aggresomes confers an advantage for bacterial survival and recovery from stress.