title: Nitrogen assimilation and nitrogen control in cyanobacteria.
abstract: Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N(2), and some cyanobacteria can also assimilate arginine or glutamine. ABC (ATP-binding cassette)-type permeases are involved in the uptake of nitrate/nitrite, urea and most amino acids, whereas secondary transporters take up ammonium and, in some strains, nitrate/nitrite. In cyanobacteria, nitrate and nitrite reductases are ferredoxin-dependent enzymes, arginine is catabolized by a combination of the urea cycle and arginase pathway, and urea is degraded by a Ni(2+)-dependent urease. These pathways provide ammonium that is incorporated into carbon skeletons through the glutamine synthetase-glutamate synthase cycle, in which 2-oxoglutarate is the final nitrogen acceptor. The expression of many nitrogen assimilation genes is subjected to regulation being activated by the nitrogen-control transcription factor NtcA, which is autoregulatory and whose activity appears to be influenced by 2-oxoglutarate and the signal transduction protein P(II). In some filamentous cyanobacteria, N(2) fixation takes place in specialized cells called heterocysts that differentiate from vegetative cells in a process strictly controlled by NtcA.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C.-Universidad de Sevilla, Américo Vespucio 49, E-41092 Seville, Spain. eflores@ibvf.csic.es
authors.forename: E
authors.initials: E
authors.lastname: Flores
authors.forename: A
authors.initials: A
authors.lastname: Herrero
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation
chemical_list: D009584:Nitrogen