Effects of Growth on Dinitrogen on the Transcriptome and Predicted Proteome of Nostoc PCC 7120

Upon growth on dinitrogen, the filamentous cyanobacterium Nostoc PCC 7120 initiates metabolic and morphological changes. We analyzed the expression of 1249 genes from major metabolic categories under nitrogen fixing and non-nitrogen fixing growth. The expression data were correlated with potential target secondary structures, probe GC-content, predicted operon structures, and nitrogen content of gene products. Of the selected genes, 494 show a more than 2-fold difference in the two conditions analyzed. Under nitrogen-fixing conditions 465 genes, mainly involved in energy metabolism, photosynthesis, respiration and nitrogenfixation, were found to be stronger expressed, whereas 29 genes showed a stronger expression under non-nitrogen fixing conditions. Analysis of the nitrogen content of regulated genes shows that Nostoc PCC 7120 growing on dinitrogen is freed from any constraints to save nitrogen. For the first time the expression of high light-induced stress proteins (HLIP-family) is shown to be linked to the nitrogen availability.