title: Metabolic Changes in Synechocystis PCC6803 upon Nitrogen-Starvation: Excess NADPH Sustains Polyhydroxybutyrate Accumulation.
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.
authors: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin Tübingen, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, Tübingen, 72070, Germany. waldemar.hauf@gmail.com.
authors: Waldemar
authors: W
authors: Hauf
authors: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin Tübingen, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, Tübingen, 72070, Germany. maximilian.schlebusch@googlemail.com.
authors: Maximilian
authors: M
authors: Schlebusch
authors: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, Golm, 14476, Germany. huege@ipk-gatersleben.de.
authors: Jan
authors: J
authors: Hüge
authors: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, Golm, 14476, Germany. kopka@mpimp-golm.mpg.de.
authors: Joachim
authors: J
authors: Kopka
authors: Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, Albert-Einstein-Str. 3, Rostock, D-18059, Germany. martin.hagemann@uni-rostock.de.
authors: Martin
authors: M
authors: Hagemann
authors: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin Tübingen, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, Tübingen, 72070, Germany. karl.forchhammer@uni-tuebingen.de.
authors: Karl
authors: K
authors: Forchhammer