FIG. 2.

Changes in cell density (A) and external NO₃⁻ (B) and external PO₄³⁻ (C) concentrations in the medium during the course of cultivation of Synechococcus sp. strain PCC 7942 in groundwater in the presence of various concentrations of phosphate. Cells had been previously deprived of PO₄³⁻ by propagating the cells in groundwater without addition of phosphate for a week. The initial PO₄³⁻ concentrations were 0.16 μM (■) (the phosphate concentration in the groundwater used), 6.6 μM (□), 14.7 μM (○), 53.7 μM (▿), and 105.3 μM (▵). The light intensity was 160 μmol m⁻² s⁻¹, the culture temperature was 32°C, and the aeration rate was ca. 0.7 vvm (error bars indicate standard deviations; n = 4).