The nitrogen-regulated response regulator NrrA is a conserved regulator of glycogen catabolism in β-cyanobacteria.

Cyanobacteria acclimatize to nitrogen deprivation by changing cellular metabolism. The nitrogen-regulated response regulator A (NrrA) is involved in regulation of carbon metabolism in response to nitrogen deprivation. However, it has not been elucidated whether these regulatory functions of NrrA are particular to a few model strains or are general among diverse cyanobacteria. In this study, we showed that regulation and functions of NrrA were highly conserved among β-cyanobacteria, which included physiologically and ecologically diverse strains. All β-cyanobacteria had the nrrA gene, while it was absent in α-cyanobacteria. The canonical NtcA-dependent promoter sequence was found upstream of the nrrA genes in most β-cyanobacteria, and its expression was indeed induced by nitrogen deprivation. Biochemical and physiological analyses of NrrA from phylogenetically distinct cyanobacteria indicated that regulation of NrrA activity and NrrA functions, namely activation of glycogen catabolism, were also common to β-cyanobacteria. These results support the conclusion that NrrA plays an important role in acclimatization to nitrogen deprivation, and that activation of glycogen catabolism is a primitive response to nitrogen deprivation in β-cyanobacteria.