PMC

Chemostats were run in high (13 mM, black bars) or low (1.3 mM, blue bars) potassium with either ammonium (left) or asparagine (right) as the sole nitrogen source. As demonstrated before, steady-state cell mass (measured here by Klett Colorimeter) decreased with lower potassium when ammonium was the nitrogen source. However, if asparagine was used as the nitrogen source, then reduced potassium had no effect on steady-state cell mass.

Ammonium uptake, fraction of nitrogen fixation and ammonium concentrations. (A,B) N uptake by Crocosphaera and non-nitrogen-fixing phytoplankton respectively. (C) Fraction of nitrogen fixation of all the N sources for Crocosphaera. (D) Ammonium concentration. The legend in (A) applies to all the figure panels. Blue curves are the default run with nitrogen fixation. Red dotted curves are the run without nitrogen fixation.

Nitrogen metabolite repression influences capsule and melanin formation. (A) India ink cell staining under light microscopy showed that wild-type H99 produces capsules that vary in size when grown on YNB supplemented with different nitrogen sources (10 mm each). Capsule size increased in the following order: (ammonium, glutamine, proline, alanine), asparagine, urea, uric acid, and creatinine. Upon coculture of each of these nitrogen sources with ammonium, capsule size was restored to that of the ammonium control. Scale bar, 10 µm. (B) Wild-type H99 produces varying amounts of melanin when grown on l-DOPA supplemented with different nitrogen sources (10 mm each). Melanization increased in the following order: (creatinine, uric acid), alanine, proline and (glutamine, asparagine, urea, ammonium). Upon coculture of each of these nitrogen sources with ammonium, melanin production was restored to that of the ammonium control, with the exception of the proline-grown cells, which melanized to the same extent with or without ammonium.

SEM image of the CTS-ZMS samples before and after ammonium nitrogen adsorption: (a) CTS-ZMS (×1000), (b) ammonium nitrogen adsorbed CTS-ZMS (×1000).