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• Hauf, W
• Schlebusch, M
• Hüge, J
• Kopka, J
• Hagemann, M
• Forchhammer, K
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• Schlebusch, M
• Hüge, J
• Kopka, J
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• Forchhammer, K
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• Schlebusch, M
• Hüge, J
• Kopka, J
• Hagemann, M
• Forchhammer, K

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Metabolites 2013, 3(1), 101-118; doi:10.3390/metabo3010101

Article

Metabolic Changes in Synechocystis PCC6803 upon Nitrogen-Starvation: Excess NADPH Sustains Polyhydroxybutyrate Accumulation

Waldemar Hauf ¹ , Maximilian Schlebusch ¹ , Jan Hüge ² , Joachim Kopka ² , Martin Hagemann ³  and Karl Forchhammer ^1,*

¹ Interfakultäres Institut für Mikrobiologie und Infektionsmedizin Tübingen, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, Tübingen, 72070, Germany ² Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, Golm, 14476, Germany ³ Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, Albert-Einstein-Str. 3, Rostock, D-18059, Germany

* Author to whom correspondence should be addressed.

Received: 20 December 2012; in revised form: 28 January 2013 / Accepted: 30 January 2013 / Published: 6 February 2013

(This article belongs to the Special Issue Metabolism in Phototrophic Prokaryotes and Algae)

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Abstract: Polyhydroxybutyrate (PHB) is a common carbon storage polymer among heterotrophic bacteria. It is also accumulated in some photoautotrophic cyanobacteria; however, the knowledge of how PHB accumulation is regulated in this group is limited. PHB synthesis in Synechocystis sp. PCC 6803 is initiated once macronutrients like phosphorus or nitrogen are limiting. We have previously reported a mutation in the gene sll0783 that impairs PHB accumulation in this cyanobacterium upon nitrogen starvation. In this study we present data which explain the observed phenotype. We investigated differences in intracellular localization of PHB synthase, metabolism, and the NADPH pool between wild type and mutant. Localization of PHB synthase was not impaired in the sll0783 mutant; however, metabolome analysis revealed a difference in sorbitol levels, indicating a more oxidizing intracellular environment than in the wild type. We confirmed this by directly measuring the NADPH/NADP ratio and by altering the intracellular redox state of wild type and sll0783 mutant. We were able to physiologically complement the mutant phenotype of diminished PHB synthase activity by making the intracellular environment more reducing. Our data illustrate that the NADPH pool is an important factor for regulation of PHB biosynthesis and metabolism, which is also of interest for potential biotechnological applications.

Keywords: cyanobacteria; metabolome; nitrogen starvation; sorbitol; NADPH/NADP ratio; redox balance; Polyhydroxybutyrate; PHB synthase 

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