FIG 2 .

The maximum cell density achieved for batch cultures grown in the dark at 16°C is plotted against addition of NH₄Cl in the presence of excess nutrients (average, n = 3 for each data point; R² = 0.80; error bars show complete range excluding one outlier shown with ×). The culturing medium is described fully in Table S1 in the supplemental material. The trend line is given by the equation y = 0.28x + 2.7, indicating a requirement of 338 attomoles of nitrogen per cell.