Decreased Effective Macromolecular Crowding in Escherichia coli Adapted to Hyperosmotic Stress

Liu, B., Hasrat, Z., Poolman, B. & Boersma, A. J., May-2019, In : Journal of Bacteriology. 201, 10, 11 p., e00708-18.

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Escherichia coli adapts to changing environmental osmolality to survive and maintain growth. It has been shown that GFP diffusion in cells adapted to osmotic upshifts is higher than expected from the increase in biopolymer volume fraction. To better understand the physicochemical state of the cytoplasm in adapted cells, we now follow the macromolecular crowding during adaptation with FRET-based sensors. We apply an osmotic upshift and find that, after an initial increase, the apparent crowding decreases over the course of hours, to arrive at a value lower than before the osmotic upshift. Crowding relates to cell volume until cell division ensues, after which a transition in the biochemical organization occurs. Analysis of single cells by microfluidics shows that changes in cell volume, elongation and division are most likely not the cause for the transition in organization. We further show that the decrease in apparent crowding upon adaptation is similar to the apparent crowding in energy-depleted cells. Based on our findings in combination with literature data, we suggest that adapted cells have indeed an altered biochemical organization of the cytoplasm, possibly due to different effective particle-size distributions and concomitant nanoscale heterogeneity. This could potentially be a general response to accommodate higher biopolymer fractions yet retaining crowding homeostasis, and could apply to other species or conditions as well.IMPORTANCE Bacteria adapt to ever changing environmental conditions such as osmotic stress and energy limitation. It is not well understood how biomolecules reorganize themselves inside Escherichia coli under these conditions. An altered biochemical organization would affect macromolecular crowding, which could influence reaction rates and diffusion of macromolecules. In cells adapted to osmotic upshift, protein diffusion is indeed faster than expected on the basis of the biopolymer volume fraction. We now probe the effects of macromolecular crowding in cells adapted to osmotic stress or depleted in metabolic energy with a genetically encoded fluorescence-based probe. We find that the effective macromolecular crowding in adapted and energy-depleted cells is lower than in unstressed cells, indicating major alterations in the biochemical organization of the cytoplasm.

Original languageEnglish
Article numbere00708-18
Number of pages11
JournalJournal of Bacteriology
Issue number10
Early online date2019
Publication statusPublished - May-2019


  • macromolecular crowding, osmotic stress, excluded volume, biochemical 17 organization of cytoplasm, energy status, FRET-based sensors

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