Time course of nitrogen-responsive transcriptomes in Nostoc sp. PCC7120

In order to analyze the responses of a heterocystous cyanobacterium to combined-nitrogen depletion/addition, we have used customized microarrays to identify genes potentially involved in heterocysts differentiation by comparing the responses in the control strain and a hetR mutant unable to differentiate heterocysts. RNA samples were isolated from cells growing in the presence of combined nitrogen (ammonium) or after 6, 8, 12 or 24 h of nitrogen deprivation. Additionally, RNA was isolated from cells growing in the absence of combined nitrogen or 8 h after addition of ammonium Nitrogen deprivation-induced expression in Nostoc sp. PCC 7120 was measured in cells subjected to nitrogen deprivation for 0, 6, 8, 12 and 24 hours. Two different experiments were performed for each time-point, except for time 0 (three experiments), and time 8 (one experiment). Additionally, samples were isolated from cells growing without combined nitrogen (one experiment) and 8 h after ammonium addition (one experiment).