Intracellular Water Exchange for Measuring the Dry Mass, Water Mass and Changes in Chemical Composition of Living Cells
Author(s)Cermak, Nathan; Son, Sungmin; Li, Yingzhong; Olcum, Selim; Higgins, John M.; Chen, Jianzhu; Grover, William H.; Manalis, Scott R.; Delgado, Francisco Feijo; Hecht, Vivian Chaya; Knudsen, Scott Michael; ... Show more Show less
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We present a method for direct non-optical quantification of dry mass, dry density and water mass of single living cells in suspension. Dry mass and dry density are obtained simultaneously by measuring a cell’s buoyant mass sequentially in an H[subscript 2]O-based fluid and a D[subscript 2]O-based fluid. Rapid exchange of intracellular H[subscript 2]O for D[subscript 2]O renders the cell’s water content neutrally buoyant in both measurements, and thus the paired measurements yield the mass and density of the cell’s dry material alone. Utilizing this same property of rapid water exchange, we also demonstrate the quantification of intracellular water mass. In a population of E. coli, we paired these measurements to estimate the percent dry weight by mass and volume. We then focused on cellular dry density – the average density of all cellular biomolecules, weighted by their relative abundances. Given that densities vary across biomolecule types (RNA, DNA, protein), we investigated whether we could detect changes in biomolecular composition in bacteria, fungi, and mammalian cells. In E. coli, and S. cerevisiae, dry density increases from stationary to exponential phase, consistent with previously known increases in the RNA/protein ratio from up-regulated ribosome production. For mammalian cells, changes in growth conditions cause substantial shifts in dry density, suggesting concurrent changes in the protein, nucleic acid and lipid content of the cell.
DepartmentDavid H. Koch Institute for Integrative Cancer Research at MIT; Massachusetts Institute of Technology. Computational and Systems Biology Program; Massachusetts Institute of Technology. Department of Biological Engineering; Massachusetts Institute of Technology. Department of Biology
Public Library of Science
Feijó Delgado, Francisco, Nathan Cermak, Vivian C. Hecht, Sungmin Son, Yingzhong Li, Scott M. Knudsen, Selim Olcum, et al. “Intracellular Water Exchange for Measuring the Dry Mass, Water Mass and Changes in Chemical Composition of Living Cells.” Edited by Michael Polymenis. PLoS ONE 8, no. 7 (July 2, 2013): e67590.
Final published version