title: The effect of ammonium on assimilatory nitrate reduction in the haloarchaeon Haloferax mediterranei.
abstract: Physiology, regulation and biochemical aspects of the nitrogen assimilation are well known in Prokarya or Eukarya but they are poorly described in Archaea domain. The haloarchaeon Haloferax mediterranei can use different nitrogen inorganic sources (NO (3) (-) , NO (2) (-) or NH (4) (+) ) for growth. Different approaches were considered to study the effect of NH (4) (+) on nitrogen assimilation in Hfx. mediterranei cells grown in KNO(3) medium. The NH (4) (+) addition to KNO(3) medium caused a decrease of assimilatory nitrate (Nas) and nitrite reductases (NiR) activities. Similar effects were observed when nitrate-growing cells were transferred to NH (4) (+) media. Both activities increased when NH (4) (+) was removed from culture, showing that the negative effect of NH (4) (+) on this pathway is reversible. These results suggest that ammonium causes the inhibition of the assimilatory nitrate pathway, while nitrate exerts a positive effect. This pattern has been confirmed by RT-PCR. In the presence of both NO (3) (-) and NH (4) (+) , NH (4) (+) was preferentially consumed, but NO (3) (-) uptake was not completely inhibited by NH (4) (+) at prolonged time scale. The addition of MSX to NH (4) (+) or NO (3) (-) cultures results in an increase of Nas and NiR activities, suggesting that NH (4) (+) assimilation, rather than NH (4) (+ ) per se, has a negative effect on assimilatory nitrate reduction in Hfx. mediterranei.
authors.affiliation: División de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Alicante, Ap. 99, 03080, Alicante, Spain. rosa.martinez@ua.es
authors.forename: Rosa María
authors.initials: RM
authors.lastname: Martínez-Espinosa
authors.forename: Belén
authors.initials: B
authors.lastname: Lledó
authors.forename: Frutos C
authors.initials: FC
authors.lastname: Marhuenda-Egea
authors.forename: María José
authors.initials: MJ
authors.lastname: Bonete
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism*; D016895:Culture Media, Serum-Free / Q000378:metabolism; D004790:Enzyme Induction; D019848:Gene Expression Regulation, Archaeal; D019623:Haloferax mediterranei / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D008717:Methionine Sulfoximine / Q000378:metabolism; D050897:Nitrate Reductase (NADPH) / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D050898:Nitrite Reductase (NAD(P)H) / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D009586:Nitrogen Fixation; D010084:Oxidation-Reduction; D017680:Potassium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors
chemical_list: D019843:Archaeal Proteins; D016895:Culture Media, Serum-Free; D009566:Nitrates; D009573:Nitrites; D017680:Potassium Compounds; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D008717:Methionine Sulfoximine; D050897:Nitrate Reductase (NADPH); D050898:Nitrite Reductase (NAD(P)H); C023844:potassium nitrate; C006568:ammonium nitrate