Proteomic profiling of the Baltic Sea cyanobacterium Nodularia spumigena strain AV1 during ammonium supplementation

The cyanobacterium Nodularia spumigena dominates the annual, toxic summer blooms in the Baltic Sea. Although Nodularia has been receiving attention due to its production of the hepatotoxin nodularin, molecular data regarding the regulation of nitrogen fixation is lacking. We have previously reported that N. spumigena strain AV1, unlike model filamentous cyanobacteria, differentiates heterocysts in the absence of detectable nitrogen fixation activity. To further analyze the uncoupling between these two linked processes, we assessed the impact of ammonium ions on the N. spumigena metabolism using a proteomic approach. Proteomic profiling was performed at three different times during ammonium supplementation using quantitative 2-dimensional gel electrophoresis followed by MS/MS analysis. Using this approach, we identified 34 proteins, 28 of which were unique proteins that changed successively in abundance during growth on ammonium. Our results indicate that N. spumigena generally exhibits lower energy production and carbon fixation in the presence of ammonium and seems to be inefficient in utilizing ammonium as an external nitrogen source. The possibility of ammonium toxicity due to PSII damage was investigated and the results are discussed. Our findings have implications in regard to the strategies considered to manage the cyanobacterial blooms in the Baltic Sea.