| Abstract: | Cells of the non-N2-fixing cyanobacterium Phormidium laminosum (Agardh) Gomont (strain OH-1-pCl1) showed doubling times of 24 h in media containing nitrate and 120 h in media without a nitrogen source. Nitrogen starvation resulted in a drastic decrease in the cellular content of chlorophyll, phycobiliproteins (phycocyanin and allophycocyanin), and other soluble proteins, although the total protein of cells was unchanged. N-starved cells showed an exocellular layer of mucilage that rapidly increased with starvation time. The appearance of N deficiency symptoms was strongly dependent on culture conditions, and it was faster under the optimal conditions used for cell growth. The relative content of C and N of nitrate-grown cells remained more or less constant during all growth phases (C/N ratio of ca. 5) but diminished at different rates in N-starved cells. Cells subjected to N starvation for 48 h had a C/N ratio of more than 10. N starvation also resulted in the selective degradation of soluble poly-peptides of masses lower than 20 kDa (which include those constituting phycobiliproteins), whereas the relative content of soluble polypeptides of greater size increased. |
