Acclimation of the global transcriptome the cyanobacterium Synechococcus sp. strain PCC 7002 to nutrient limitations and different nitrogen sources

The unicellular, euryhaline cyanobacterium Synechococcus sp. PCC 7002 is known for its tolerance to high light intensities, its genome encodes about 3200 proteins. The present study focuses on changes of the transcript level as a response to limitation of the major nutrients CO2, nitrogen source, sulfate, phosphate and iron compared to cells grown under optimal conditions. Further, transcriptional changes were investigated and compared from cells grown with ammonia, urea and nitrate as nitrogen source. Nutrient limitations caused a strong decrease of transcript levels of the genes coding for the major metabolic pathways, especially of the photosynthetic apparatus, CO2 fixation pathway and protein biosynthesis. Uptake mechanisms for the respective nutrients were strongly up-regulated; and other nutrient-specific changes such as modifications of the photosynthetic antenna complex with the IsiA protein upon iron limitation were observed on the mRNA levels. The transcription data further suggest changes of the composition of the NADH dehydrogenase complex upon several nutrient limitations, ndhD2 encoding a variant of the NdhD subunit showed a strong increase of mRNA. Up regulation of transcripts for flavoproteins was also observed, especially when CO2 as photosynthetic electron acceptor is limiting. Genes involved in oxidative stress response show a constitutively high transcript level, even under standard growth conditions. The global transcriptomes of cells grown with ammonia or urea as nitrogen source showed increased transcript levels of the CO2 fixation machinery compared to cells grown with nitrate, ; nitrate uptake and reduction shows down regulation,pointing to an increased growth rate of the respective cultures whereas other changes of the transcriptome were only minor.