Regulation of nitrate reduction in a cyanobacterium : Distinctive modes of ammonium-repression of nitrate and nitrite reductases

Gene Expression in Two Cyanobacteria, Freshwater Synechococcus sp. PCC 7942 and Oceanic Synechococcus sp. WH 7803, in response to ammonium, nitrate or iron

“…Nitrate reduction is tightly dependent on the photogenerated reductants that are supplied during the light reactions of photosynthesis. Ferredoxin supplies electrons for the reductive reactions catalyzed by nitrate reductase and nitrite reductase (Flores et al, 1983b;Palod et al, 1990;…”

Effect of Glucose Utilization on Nitrite Excretion by the Unicellular Cyanobacterium Synechocystis sp. Strain PCC 6803

“…The reduction of nitrate in these organisms is a true photosynthetic process, which requires eight electrons donated by reduced ferredoxin, two for nitrate reductase and six for nitrite reductase (2, 5). The regulation of nitrate assimilation in cyanobacteria of the genera Synechococcus and Anabaena, in which the synthesis of nitrate and nitrite reductases is regulated by the nitrogen source, has been extensively studied; ammonium is a repressor in all cyanobacteria examined thus far (5)(6)(7)(8)11).…”