EFFECT OF NITROGEN STARVATION ON THE BIOCHEMISTRY OF PHORMIDIUM-LAMINOSUM (CYANOPHYCEAE)

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 (CIN ratio of ca. 5) but diminished at different rates in N-starved cells. Cells subjected to N starvation for 48 h had a CIN ratio of more than 10. N starvation also resulted in the selective degradation of soluble polypeptides of masses lower than 20 kDa (which include those constituting phycobiliproteins), whereas the relative content of soluble polypeptides of greater size increased.