Differences in the accumulation of phosphorus between vegetative cells and heterocysts in the cyanobacterium Nodularia spumigena

The cyanobacterium Nodularia spumigena is a species that frequently forms blooms in the Baltic Sea. Accumulation of the vital nutrient phosphorus (P) apparently plays an important role in the ability of this and other cyanobacteria to grow even when dissolved inorganic phosphorus is depleted. However, until now, this has not been studied in N. spumigena at the cellular level. Therefore, in this study, phosphorus incorporation and distribution in cyanobacterial filaments over time was examined by scanning electron microscopy in combination with energy dispersive X-ray analysis (SEM/EDX) and nanoscale secondary ion mass spectrometry (NanoSIMS). Immediately after phosphate addition to a phosphorus-depleted population, the phosphate concentration decreased in the water while intracellular polyphosphate accumulated. Microscopically, phosphorus in form of polyphosphate granules was stored preferentially in vegetative cells, whereas heterocysts remained low in intracellular phosphorus. This information is an essential step towards understanding the phosphorus dynamics of this species and demonstrates that the division of tasks between vegetative cells and heterocysts is not restricted to nitrogen fixation.