Figure 7. Partial dehydration reduces density differences between cell populations.

C. vulgaris biomass was measured during lag phase, log phase and stationary phase in TP with 100 mM glucose. (a) Flow cytometry was used to estimate average cell diameter using SSC-W measurements and plotted vs average dry weight per cell. Flow cytometry was performed on cells diluted into TP growth medium (▵) or hypertonic media (1 M NaCl in TP) (▵) and allowed to dehydrate for 10min. The use of NaCl improves the linearity of the relationship between biovolume and biomass dry weight. All measurements were conducted in triplicate; error bars represent the standard error of the mean. (b) Percoll density gradient centrifugation demonstrates a lower, more uniform range of cell densities when measured in medium containing 1 M NaCl. Tubes are labelled as follows: (1) C. vulgaris in TP. (2) C. vulgaris + 1 M NaCl. (3) C. vulgaris in TAP. (4) C. vulgaris in TAP + 1 M NaCl 1 M. (5) C. vulgaris in TP + glucose (100 mM). (6) C. vulgaris in TP + glucose (100 mM) + 1 M NaCl. (7) Standard density marker beads (g.mL⁻¹) with densities indicated.