This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplemental material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Konopka, M. C.
Right arrow Articles by Weisshaar, J. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Konopka, M. C.
Right arrow Articles by Weisshaar, J. C.

 Previous Article  |  Next Article 

Journal of Bacteriology, January 2009, p. 231-237, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00536-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cytoplasmic Protein Mobility in Osmotically Stressed Escherichia coli{triangledown} ,{dagger}

Michael C. Konopka,1,{ddagger} Kem A. Sochacki,1 Benjamin P. Bratton,1 Irina A. Shkel,1 M. Thomas Record,1,2 and James C. Weisshaar1*

Department of Chemistry, 1101 University Avenue,1 Department of Biochemistry, University of Wisconsin—Madison, Madison, Wisconsin 537062

Received 18 April 2008/ Accepted 7 October 2008

Facile diffusion of globular proteins within a cytoplasm that is dense with biopolymers is essential to normal cellular biochemical activity and growth. Remarkably, Escherichia coli grows in minimal medium over a wide range of external osmolalities (0.03 to 1.8 osmol). The mean cytoplasmic biopolymer volume fraction (<{phi}>) for such adapted cells ranges from 0.16 at 0.10 osmol to 0.36 at 1.45 osmol. For cells grown at 0.28 osmol, a similar <{phi}> range is obtained by plasmolysis (sudden osmotic upshift) using NaCl or sucrose as the external osmolyte, after which the only available cellular response is passive loss of cytoplasmic water. Here we measure the effective axial diffusion coefficient of green fluorescent protein (DGFP) in the cytoplasm of E. coli cells as a function of <{phi}> for both plasmolyzed and adapted cells. For plasmolyzed cells, the median DGFP (Formula) decreases by a factor of 70 as <{phi}> increases from 0.16 to 0.33. In sharp contrast, for adapted cells, Formula decreases only by a factor of 2.1 as <{phi}> increases from 0.16 to 0.36. Clearly, GFP diffusion is not determined by <{phi}> alone. By comparison with quantitative models, we show that the data cannot be explained by crowding theory. We suggest possible underlying causes of this surprising effect and further experiments that will help choose among competing hypotheses. Recovery of the ability of proteins to diffuse in the cytoplasm after plasmolysis may well be a key determinant of the time scale of the recovery of growth.

* Corresponding author. Mailing address: Department of Chemistry, 1101 University Ave., Madison, WI 53706. Phone: (608) 262-0266. Fax: (608) 262-0453. E-mail: weisshaar{at}chem.wisc.edu

{triangledown} Published ahead of print on 24 October 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Department of Chemical Engineering, University of Washington, Box 355014, Seattle, WA 98195-5014.

Journal of Bacteriology, January 2009, p. 231-237, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00536-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»