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Single-Molecule Tracking Microscopy - A Tool for Determining the Diffusive States of Cytosolic Molecules
Published on: September 5, 2019
Bacterial chromosomal loci move subdiffusively through a viscoelastic cytoplasm
Stephanie C Weber1, Andrew J Spakowitz, Julie A Theriot
1Department of Biochemistry, Stanford University, Stanford, California 94305, USA.
Physical Review Letters
|September 28, 2010
Summary
Bacterial DNA motion scales robustly, suggesting polymer relaxation in the cytoplasm. This movement aligns with fractional Langevin motion, not random walks, in live cells.
Area of Science:
- Microbial genetics and cell biology
- Polymer physics in biological systems
- Biophysics of intracellular transport
Background:
- Understanding DNA dynamics is crucial for bacterial cell function.
- Previous models struggled to explain anomalous diffusion of chromosomal loci.
- The bacterial cytoplasm presents a complex viscoelastic environment.
Purpose of the Study:
- To investigate the diffusive motion of chromosomal loci in live bacteria.
- To determine the physical model that best describes this motion.
- To elucidate the role of DNA polymer dynamics and cytoplasmic environment.
Main Methods:
- Tracking fluorescently labeled chromosomal loci in real-time within live bacterial cells.
- Analyzing the mean square displacement (MSD) and velocity autocorrelation functions.
- Comparing experimental data to predictions from Rouse polymer dynamics and anomalous diffusion models.
Main Results:
- Observed a robust scaling of mean square displacement (MSD) with time (τ^0.39).
- Demonstrated ergodicity in both time-averaged and ensemble-averaged MSD.
- Found a negative velocity autocorrelation at short time lags.
- Data strongly supports fractional Langevin motion.
Conclusions:
- Bacterial chromosomal motion is governed by the relaxation of Rouse modes of the DNA polymer.
- The viscoelastic nature of the bacterial cytoplasm significantly influences DNA dynamics.
- Fractional Langevin motion provides a consistent framework for anomalous diffusion in vivo, ruling out continuous time random walk models.
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