Molecular sieving properties of the cytoplasm of Escherichia coli and consequences of osmotic stress

Mol Microbiol. 2010 Jul 1;77(1):200-7. doi: 10.1111/j.1365-2958.2010.07201.x. Epub 2010 May 12.


We determined the diffusion coefficients (D) of (macro)molecules of different sizes (from approximately 0.5 to 600 kDa) in the cytoplasm of live Escherichia coli cells under normal osmotic conditions and osmotic upshift. D values decreased with increasing molecular weight of the molecules. Upon osmotic upshift, the decrease in D of NBD-glucose was much smaller than that of macromolecules. Barriers for diffusion were found in osmotically challenged cells only for GFP and larger proteins. These barriers are likely formed by the nucleoid and crowding of the cytoplasm. The cytoplasm of E. coli appears as a meshwork allowing the free passage of small molecules while restricting the diffusion of bigger ones.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytoplasm / chemistry*
  • Cytoplasm / metabolism*
  • Diffusion*
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism
  • Organic Chemicals / metabolism
  • Osmotic Pressure*


  • Escherichia coli Proteins
  • Organic Chemicals