Fig. 3

Characterization of cells under osmotic adaptation. a–c Monitored phase shifts (\(\hat \phi\)) (b) and projected cell areas (c) of the four cells shown in a during osmoadaptation (black arrow indicates time point of osmotic upshift). The line colors correspond to the cell numbers in a. Scale bar in a is 5 μm. d, e Inferred cell volume V_cell(t) (d) and the relative cell mass m_dry(t) − m₀ (e), where m₀ denotes the cell mass prior to osmotic upshift. f Relative cell mass m_dry(t) − m₀ as a function of relative cell volume V_cell(t) − V_m, where V_m denotes the minimum cell volume attained after initial water outflux, at different stages in the osmoadaptation for the cells shown in a. The initial relative cell masses and relative volumes are shown as open diamonds. Immediately upon exposure to a high osmolarity medium, the cells expel water and reduce in volume while retaining their mass, shifting horizontally in the figure. Thereafter the cells slowly expand while gaining in mass (colored squares). The black dashed line represents the expected cell mass increase for accumulation of glycerol. The red dashed line represents the expected mass increase with volume had the cell swelling  been a result of metabolic cell growth. g The rate of osmolyte production increases will cell size (V_m) with a typical production rate of 0.5 mM s⁻¹ (red dashed line). h The estimated value of the parameter K defined in the main text for N = 57 cells is consistent with accumulation of primarily glycerol (K = 0.011 ml mol⁻¹ shown as dashed black line). Also shown are the expected values of K for glucose (K = 0.028 ml mol⁻¹ shown as red dashed line) and trehalose (K = 0.053 ml mol⁻¹ shown as blue dashed line) Inset: Small cells appear to accumulate compounds with slightly larger values of K. The blue dashed line corresponds to the value of K for glycerol. The cell volume is here taken to mean the minimum cell volume after osmotic upshift (V_m)