Assimilatory Nitrogen Metabolism and Its Regulation

Flores, Enrique; Herrero, Antonia

doi:10.1007/0-306-48205-3_16

Cited by 102 publications

(181 citation statements)

References 185 publications

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“…These results are in agreement with earlier reports of partial repression of nitrate reductase activity by arginine in Anabaena 7120 18 and Nostoc ANTH 20 , but in contrast to the reported induction of NR activity by arginine in Oscillatoria chalybea 24 . The fact that NR activity was repressed by NH 4 + and derepressed in its absence is consistent with earlier reports that in some cyanobacteria NR is NH 4 + repressible-derepressible [25][26][27][28] .…”

Section: Resultssupporting

confidence: 92%

Isolation and characterization of a Mastigocladus species capable of growth, N2-fixation and N-assimilation at elevated temperature

et al. 2007

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A Mastigocladus species was isolated from the hot spring of Jakrem (Meghalaya) India. Uptake and utilization of nitrate, nitrite, ammonium and amino acids (glutamine, asparagine, arginine, alanine) were studied in this cyanobacterium grown at different temperatures (25ºC, 45ºC). There was 2-3 fold increase in the heterocyst formation and nitrogenase activity in N-free medium at higher temperature (45ºC). Growth and uptake and assimilation of various nitrogen sources were also 2-3 fold higher at 45ºC indicating that it is a thermophile. The extent of induction and repression of nitrate uptake by NO 3¯ and NH 4 + , respectively, differed from that of nitrite. It appeared that Mastigocladus had two independent nitrate/nitrite transport systems. Nitrate reductase and nitrite reductase activitiy was not NO 3¯-inducible and ammonium or amino acids caused only partial repression. Presence of various amino acids in the media partially repressed glutamine synthetase activity. Ammonium (methylammonium) and amino acid uptake showed a biphasic pattern, was energy-dependent and the induction of uptake required de novo protein synthesis. Ammonium transport was substrate (NH 4 + ) -repressible, while the amino acid uptake was substrate inducible. When grown at 25ºC, the cyanobacterium formed maximum akinetes that remained viable upto 5 years under dry conditions.

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Section: Resultssupporting

confidence: 92%

Isolation and characterization of a Mastigocladus species capable of growth, N2-fixation and N-assimilation at elevated temperature

et al. 2007

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“…In the so-called cyclic electron transport around PSI, electrons transferred from PSI to ferredoxin can be fed back to the cyt b 6 f complex, thereby increasing proton translocation and thus ATP synthesis (Stroebel et al 2003). Electrons needed in N 2 fixation are allocated from the reduced ferredoxin onto nitrogenase (Flores and Herrero 1994). Therefore, N 2 fixation represents a strong quenching mechanism in Trichodesmium, yielding an oxidized PQ pool and improved electron transport.…”

Section: Photosynthesis and Electron Transportmentioning

confidence: 99%

Interactions between CCM and N2 fixation in Trichodesmium

2010

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In view of the current increase in atmospheric pCO 2 and concomitant changes in the marine environment, it is crucial to assess, understand, and predict future responses of ecologically relevant phytoplankton species. The diazotrophic cyanobacterium Trichodesmium erythraeum was found to respond strongly to elevated pCO 2 by increasing growth, production rates, and N 2 fixation. The magnitude of these CO 2 effects exceeds those previously seen in other phytoplankton, raising the question about the underlying mechanisms. Here, we review recent publications on metabolic pathways of Trichodesmium from a gene transcription level to the protein activities and energy fluxes. Diurnal patterns of nitrogenase activity change markedly with CO 2 availability, causing higher diel N 2 fixation rates under elevated pCO 2 . The observed responses to elevated pCO 2 could not be attributed to enhanced energy generation via gross photosynthesis, although there are indications for CO 2 -dependent changes in ATP/ NADPH ? H ? production. The CO 2 concentrating mechanism (CCM) in Trichodesmium is primarily based on HCO 3 -uptake. Although only little CO 2 uptake was detected, the NDH complex seems to play a crucial role in internal cycling of inorganic carbon, especially under elevated pCO 2 . Affinities for inorganic carbon change over the day, closely following the pattern in N 2 fixation, and generally decrease with increasing pCO 2 . This down-regulation of CCM activity and the simultaneously enhanced N 2 fixation point to a shift in energy allocation from carbon acquisition to N 2 fixation under elevated pCO 2 levels. A strong light modulation of CO 2 effects further corroborates the role of energy fluxes as a key to understand the responses of Trichodesmium.

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“…This regulation is referred to as global nitrogen control (7). Assimilation of nitrogen is stringently regulated to the extent that in the presence of ammonium, these organisms preferentially utilize ammonium over alternative inorganic sources such as nitrate, nitrite, or gaseous nitrogen (5). It has been shown in Synechococcus sp.…”

mentioning

confidence: 99%

“…Furthermore, the presence of ammonium results in inhibition of nitrogen fixation and heterocyst development in Anabaena sp. strain PCC 7120 (5,24).…”

mentioning

confidence: 99%

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Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K

Bradley

Reddy

1997

J Bacteriol

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In cyanobacteria, ammonium represses expression of proteins involved in nitrogen fixation and assimilation. The global nitrogen regulator gene ntcA encodes a DNA-binding protein, NtcA, that is a transcriptional activator of genes subject to nitrogen control. We report the cloning and sequencing of the ntcA gene from a nitrogen-fixing unicellular cyanobacterium, Cyanothece sp. strain BH68K. The gene comprises 678 nucleotides, and the deduced NtcA protein contains 226 amino acids with a predicted molecular weight of 25,026. In addition, ntcA mRNA levels were measured in cells grown under different nitrogen regimes. Under nitrogenfixing conditions, ntcA transcripts were weakly expressed. Furthermore, ntcA expression was diminished or inversely proportional to nifHDK expression. Conversely, ntcA expression increased in nitrate-grown cells, and a concentration-dependent increase was seen in ammonium-grown cells up to 1 mM NH 4 Cl. These results indicate that ntcA is involved more in nitrogen assimilation than in nitrogen fixation and also imply that the rhythmic expression of ntcA and nifHDK transcription may be under the control of a circadian clock.

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Assimilatory Nitrogen Metabolism and Its Regulation

Cited by 102 publications

References 185 publications

Isolation and characterization of a Mastigocladus species capable of growth, N2-fixation and N-assimilation at elevated temperature

Isolation and characterization of a Mastigocladus species capable of growth, N2-fixation and N-assimilation at elevated temperature

Interactions between CCM and N2 fixation in Trichodesmium

Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K

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