Limits...
Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink.

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors.It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

View Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

ABSTRACT
Nitrogen starvation acclimation in non-diazotrophic cyanobacteria is characterized by a process termed chlorosis, where the light harvesting pigments are degraded and the cells gradually tune down photosynthetic and metabolic activities. The chlorosis response is governed by a complex and poorly understood regulatory network, which converges at the expression of the nblA gene, the triggering factor for phycobiliprotein degradation. This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation. Inhibition of glutamine synthetase (GS) by a precise dosage of l-methionine-sulfoximine (MSX) mimics the metabolic situation of nitrogen starvation. Addition of nitrate to such MSX-inhibited cells eliminates the associated redox-stress by enabling electron flow towards nitrate/nitrite reduction and thereby, prevents the induction of nblA expression and the associated chlorosis response. This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors. It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

No MeSH data available.


Related in: MedlinePlus

Absorbance spectra between 550 and 750 nm of S. elongatus PCC 7942 grown for 3 days in nitrate (A) or ammonia (B) containing medium after treatment with 2 µM MSX. To visualize the specific absorption of the pigments, the spectra were first normalized to an OD750 of 1, then subtracted by 1 (to set the OD750 to zero). Subsequently, a baseline correction was performed between OD750 and OD550 to eliminate light scattering effects.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4390884&req=5

life-05-00888-f006: Absorbance spectra between 550 and 750 nm of S. elongatus PCC 7942 grown for 3 days in nitrate (A) or ammonia (B) containing medium after treatment with 2 µM MSX. To visualize the specific absorption of the pigments, the spectra were first normalized to an OD750 of 1, then subtracted by 1 (to set the OD750 to zero). Subsequently, a baseline correction was performed between OD750 and OD550 to eliminate light scattering effects.

Mentions: To confirm the results shown above with pure S. elongatus wild-type cells, we analyzed phycobiliprotein degradation as the hallmark of chlorosis and read-out of nblA expression. In agreement with the inhibition of nblA::luxAB expression in the reporter strain, the presence of nitrate inhibited MSX-induced phycobiliprotein degradation in S. elongatus wild-type cells. Whereas in the presence of ammonium, 2 µM MSX treatment led to an almost complete degradation of phycobiliproteins (visible at the absorption peak at 625 nm), no phycobiliprotein degradation occurred in nitrate-supplemented medium as shown in Figure 6.


Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink.

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Absorbance spectra between 550 and 750 nm of S. elongatus PCC 7942 grown for 3 days in nitrate (A) or ammonia (B) containing medium after treatment with 2 µM MSX. To visualize the specific absorption of the pigments, the spectra were first normalized to an OD750 of 1, then subtracted by 1 (to set the OD750 to zero). Subsequently, a baseline correction was performed between OD750 and OD550 to eliminate light scattering effects.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390884&req=5

life-05-00888-f006: Absorbance spectra between 550 and 750 nm of S. elongatus PCC 7942 grown for 3 days in nitrate (A) or ammonia (B) containing medium after treatment with 2 µM MSX. To visualize the specific absorption of the pigments, the spectra were first normalized to an OD750 of 1, then subtracted by 1 (to set the OD750 to zero). Subsequently, a baseline correction was performed between OD750 and OD550 to eliminate light scattering effects.
Mentions: To confirm the results shown above with pure S. elongatus wild-type cells, we analyzed phycobiliprotein degradation as the hallmark of chlorosis and read-out of nblA expression. In agreement with the inhibition of nblA::luxAB expression in the reporter strain, the presence of nitrate inhibited MSX-induced phycobiliprotein degradation in S. elongatus wild-type cells. Whereas in the presence of ammonium, 2 µM MSX treatment led to an almost complete degradation of phycobiliproteins (visible at the absorption peak at 625 nm), no phycobiliprotein degradation occurred in nitrate-supplemented medium as shown in Figure 6.

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors.It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

View Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

ABSTRACT
Nitrogen starvation acclimation in non-diazotrophic cyanobacteria is characterized by a process termed chlorosis, where the light harvesting pigments are degraded and the cells gradually tune down photosynthetic and metabolic activities. The chlorosis response is governed by a complex and poorly understood regulatory network, which converges at the expression of the nblA gene, the triggering factor for phycobiliprotein degradation. This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation. Inhibition of glutamine synthetase (GS) by a precise dosage of l-methionine-sulfoximine (MSX) mimics the metabolic situation of nitrogen starvation. Addition of nitrate to such MSX-inhibited cells eliminates the associated redox-stress by enabling electron flow towards nitrate/nitrite reduction and thereby, prevents the induction of nblA expression and the associated chlorosis response. This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors. It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

No MeSH data available.


Related in: MedlinePlus