![]() ![]() Although dry mass can be measured in living cells by quantitative phase microscopy, the conversion factor between refractive index and dry mass concentration must be known. Dry and wet mass are typically obtained by weighing a population before and after baking to remove the intracellular water. Despite the fundamental significance of these physical parameters, the techniques for measuring them directly, particularly in living cells, are limited. Bacteria and yeast increase their ribosomal RNA content to achieve faster growth rates –, the wet and dry content of yeast can change disproportionately during the cell cycle – and the water content of mammalian cells is reduced following apoptosis. The dry and wet content of the cell as well as its overall chemical composition are tightly regulated in a wide range of cellular processes. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials. is a co-founder of Affinity Biosensors and declares competing financial interests. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: S.R.M. acknowledges support from Fundação para a Ciência e a Tecnologia, Portugal, through a graduate fellowship (SFRH/BD/47736/2008). Institute for Collaborative Biotechnologies through contract number W911NF-09-D-0001 from the United States Army Research Office. Center for Cell Decision Process Grant (P50GM68762) and contract R01CA170592, both from the United States National Institutes of Health. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: Physical Sciences Oncology Center at the Massachusetts Institute of Technology (U54CA143874) from the United States National Cancer Institute. Received: ApAccepted: Published: July 2, 2013Ĭopyright: © 2013 Feijó Delgado et al. PLoS ONE 8(7):Įditor: Michael Polymenis, Texas A&M University, United States of America (2013) Intracellular Water Exchange for Measuring the Dry Mass, Water Mass and Changes in Chemical Composition of Living Cells. 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.Ĭitation: Feijó Delgado F, Cermak N, Hecht VC, Son S, Li Y, Knudsen SM, et al. cerevisiae, dry density increases from stationary to exponential phase, consistent with previously known increases in the RNA/protein ratio from up-regulated ribosome production. 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. We then focused on cellular dry density – the average density of all cellular biomolecules, weighted by their relative abundances. coli, we paired these measurements to estimate the percent dry weight by mass and volume. Utilizing this same property of rapid water exchange, we also demonstrate the quantification of intracellular water mass. Rapid exchange of intracellular H 2O for D 2O 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. ![]() Dry mass and dry density are obtained simultaneously by measuring a cell’s buoyant mass sequentially in an H 2O-based fluid and a D 2O-based fluid. We present a method for direct non-optical quantification of dry mass, dry density and water mass of single living cells in suspension. ![]()
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