Effect of Nitrogen Source on Cyanophycin Synthesis

Experiments were carried out to examine the effects of nitrogen source on nitrogen incorporation into cyanophycin during nitrogen limitation and repletion, both with or without inhibition of protein synthesis, in cyanobacteria grown on either nitrate or ammonium. The use of nitrate and ammonium, 14N labeled in the growth medium and 15N labeled in the repletion medium, allows the determination of the source of nitrogen in cyanophycin using proton nuclear magnetic resonance spectroscopy. The data suggest that nitrogen from both the breakdown of cellular protein (14N) and directly from the medium (15N) is incorporated into cyanophycin. Nitrogen is incorporated into cyanophycin at different rates and to different extents, depending on the source of nitrogen (ammonium or nitrate) and whether the cells are first starved for nitrogen. These differences appear to be related to the activity of nitrate reductase in cells and to the possible expression of cyanophycin synthetase during nitrogen starvation. Cyanobacteria are capable of growing on a number of dif-ferent nitrogen sources. Nitrate, nitrite, ammonium, urea, sev-eral amino acids, atmospheric nitrogen, nucleosides, and bases all have been reported to be assimilated by some cyanobacte-ria, but ammonium appears to be assimilated preferentially (7