The effect of ammonium on assimilatory nitrate reduction in the haloarchaeon Haloferax mediterranei |
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Authors: | Rosa María Martínez-Espinosa Belén Lledó Frutos C. Marhuenda-Egea María José Bonete |
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Affiliation: | (1) División de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Alicante, Ap. 99, 03080 Alicante, Spain |
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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 (NO3−, NO2− or NH4+) for growth. Different approaches were considered to study the effect of NH4+ on nitrogen assimilation in Hfx. mediterranei cells grown in KNO3 medium. The NH4+ addition to KNO3 medium caused a decrease of assimilatory nitrate (Nas) and nitrite reductases (NiR) activities. Similar effects were observed when nitrate-growing cells were transferred to NH4+ media. Both activities increased when NH4+ was removed from culture, showing that the negative effect of NH4+ 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 NO3− and NH4+, NH4+ was preferentially consumed, but NO3− uptake was not completely inhibited by NH4+ at prolonged time scale. The addition of MSX to NH4+ or NO3− cultures results in an increase of Nas and NiR activities, suggesting that NH4+ assimilation, rather than NH4+ per se, has a negative effect on assimilatory nitrate reduction in Hfx. mediterranei. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Halophile Archaeon Nitrate assimilation Ammonium assimilation Nitrogen regulation Nitrate reductase Nitrite reductase |
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