Molecular Biology

Glassy Cytoplasm

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Science  07 Feb 2014:
Vol. 343, Issue 6171, pp. 580-581
DOI: 10.1126/science.343.6171.580-d

Bacteria lack motor proteins such as myosins, kinesins, and dyneins, and molecular transport and cytoskeletal mixing are thought to rely on diffusion. Using single-molecule tracking, Parry et al. found that the mobility of protein filaments, large granules, and plasmids was higher in metabolically active cells. They developed a probe, based on a GFP-labeled self-assembling reovirus protein, in which size could be tuned by protein expression. Metabolically dependent motility of the probe was dependent on size, with particles of about 30 nm and higher showing significantly higher mean square displacements in metabolically active cells. The motion of large particles was characteristic of movement in a glass-forming liquid approaching the glass transition. The distribution of displacements was non-Gaussian, the system non-ergodic, and the cytoplasm displayed dynamic heterogeneity with regions of both high and low particle motility. Metabolic activity fluidized the cytoplasm so that large particles could escape a caged environment. As a result, a higher fraction of particles showed large displacements in active cells. These properties of the bacterial cytoplasm need to be taken into account in understanding bacterial physiology, particularly transitions between dormancy and growth.

Cell 10.1016/j.cell.2013.11.028 (2014).

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