FIG. 1.

Effects of phosphate, sulfate, and ammonium limitation on cyanophycin accumulation in A. calcoaceticus. Cells were cultivated for 44 h at 30°C in 250-ml Erlenmeyer flasks without baffles containing 100 ml of Tris-HCl-buffered MSM with 107 mM sodium glutamate (•) or 107 mM sodium gluconate (▴) as the sole carbon source. The basic medium was prepared as described in Materials and Methods except for the nutrient investigated. At the end of the experiment, the cells were harvested by centrifugation, and the cyanophycin content was analyzed. (A) The phosphate concentration was varied between 42 μM and 2.0 mM. (B) The sulfate concentration was varied between 0.01 and 0.25 mM by varying the amount of (NH₄)₂SO₄ added to the medium. The concentration of ammonium was kept constant at 30 mM by adding the appropriate amount of NH₄Cl to the medium. (C) The ammonium concentration was varied between 0.1 and 10 mM by varying the amount of (NH₄)₂SO₄ added to the medium. The concentration of sulfate ions was kept constant at 15 mM by adding the appropriate amount of MgSO₄ · 7H₂O to the medium.