| The physical nature of the bacterial cytoplasm is poorly understood even though it determines cytoplasmic dynamics and hence sets limits on cellular physiology and behavior. Through single-particle tracking of protein filaments, plasmids, storage granules and foreign particles of different sizes, I find that the bacterial cytoplasm displays properties characteristic of glass-forming liquids near the glass transition. The cytoplasm changes from liquid-like to solid-like in a component size-dependent fashion. As a result, the motion of cytoplasmic components becomes disproportionally constrained with increasing size. Remarkably, cellular metabolism tends to fluidize the cytoplasm, allowing larger components to escape their local environment and explore larger regions of the cytoplasm. Fluidization is incomplete throughout populations of cells, and produces a broad distribution of dynamics and may have implications for phenotypic heterogeneity. Ultimately, cytoplasmic fluidity and dynamics dramatically change as cells shift between metabolically active and dormant states in response to fluctuating environments. These findings provide insight into bacterial dormancy and have broad implications to our understanding of bacterial physiology as the glassy behavior of the cytoplasm impacts all intracellular processes involving large components. |
