Content area
Full Text
BRIEF COMMUNICATIONS
Using buoyant mass to measure the growth of single cells
2010 Nature America, Inc. All rights reserved.
Michel Godin1,6,7, Francisco Feij Delgado1,7, Sungmin Son2, William H Grover1, Andrea K Bryan1, Amit Tzur3, Paul Jorgensen3,6, Kris Payer4,Alan D Grossman5, Marc W Kirschner3 &Scott R Manalis1,2
We used a suspended microchannel resonator (SMR) combined with picoliter-scale microuidic control to measure buoyant mass and determine the instantaneous growth rates of individualcells. The SMR measures mass with femtogram precision, allowing rapid determination of the growth rate in a fraction of a complete cell cycle. We found that for individual cells of Bacillus subtilis, Escherichia coli, Saccharomyces cerevisiae and mouse lymphoblasts, heavier cells grew faster than lighter cells.
Understanding how the rate of cell growth changes during the cell cycle and in response to growth factors and other stimuli is of fundamental interest. Over the decades, various approaches have been developed for describing cellular growth patterns, but different studies have often reached irreconcilable conclusions, even for the same cell types. The debate has focused on whether cells grow at a constant rate (linear) or at a rate that is dependent on their size (exponential), although more complex growth curves have also been suggested. The mean dry mass accumulation of E. coli has been reported as increasing linearly1, and cell length growth has been described as bilinear2, bilinear and trilinear3, and exponential4. The size of the budding yeast S. cerevisiae has been observed to increase exponentially by some approaches5,6,
but to have a nonexponential and cell cycledependent growth curve by others7. For mammalian cells, volume measurements have shown linear growth for rat Schwann cells8 and exponential growth, with a varying rate constant, for mouse lymphoblast cells9. Several factors may contribute to the discrepancies between different growth models: (i) cells are minute, irregularly shaped objects; (ii) proliferating cells increase their size only by a factor of 2, so distinguishing between different cell growth models with mathematical rigor requires highly precise measurements; (iii) a wide variety of methods have been used to measure growth,
including approaches that average across populations as well as those that monitor individual cells; and (iv) a cells size includes both volume and mass, which can change at different rates.
Although both mass and volume are important...