title: Molecular characterization of nitrate uptake and assimilatory pathway in Arthrospira platensis reveals nitrate induction and differential regulation.
abstract: The nitrate assimilation pathway and its regulation in the high-protein neutraceutical cyanobacterium, Arthrospira (Spirulina), were studied. A complete characterization of the genes of the nitrate uptake and assimilatory pathway in Arthrospira platensis strain PCC 7345 was done including cloning, sequencing, phylogenetic analysis and expression studies. Genomic localization studies revealed that their clustering is different from the operons known in other cyanobacteria; only nrtP and narB are organized together, while nirA, glnA and gltS exist in separate genomic locations. The presence of both types of nitrate transporters (nrtP/ABC types) in A. platensis is rare, as their occurrence is usually specific to marine and freshwater microorganisms, respectively. The positive effect of nitrate on transcript accumulation of narB, nirA and nrtP genes in N-depleted and N-restored cultures confirmed nitrate induction, which is abolished by the addition of ammonium ions into the medium. Gene expression studies in response to nitrate, nitrite, ammonium and glutamine provided the first evidence of differential regulation of multiple genes of nitrate assimilatory pathway in Arthrospira.
authors.affiliation: School of Biotechnology, Guru Gobind Singh Indraprastha University, Sector-16 C, Dwarka, 110078, New Delhi, India.
authors.forename: Sunila
authors.initials: S
authors.lastname: Lochab
authors.forename: Polumetla Ananda
authors.initials: PA
authors.lastname: Kumar
authors.forename: Nandula
authors.initials: N
authors.lastname: Raghuram
mesh_terms: D064751:Ammonium Compounds / Q000494:pharmacology; D027321:Anion Transport Proteins / Q000235:genetics; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D023061:Gene Order; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D005973:Glutamine / Q000494:pharmacology; D008969:Molecular Sequence Data; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism / Q000494:pharmacology; D010802:Phylogeny
chemical_list: D064751:Ammonium Compounds; D027321:Anion Transport Proteins; D000091285:Nitrate Transporters; D009566:Nitrates; D009573:Nitrites; D005973:Glutamine; D009572:Nitrite Reductases; D050901:Nitrate Reductase; D005974:Glutamate-Ammonia Ligase