Hauf Waldemar, Schlebusch Maximilian, Hüge Jan, Kopka Joachim, Hagemann Martin, Forchhammer Karl
Interfakultäres Institut für Mikrobiologie und Infektionsmedizin Tübingen, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, Tübingen, 72070, Germany.
Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, Golm, 14476, Germany.
Metabolites. 2013 Feb 6;3(1):101-18. doi: 10.3390/metabo3010101.
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.
聚羟基丁酸酯（PHB）是异养细菌中常见的碳储存聚合物。它也在一些光合自养蓝细菌中积累；然而，关于该类群中PHB积累如何调控的知识有限。集胞藻PCC 6803中的PHB合成在诸如磷或氮等大量营养素受限后启动。我们之前报道过基因sll0783中的一个突变，该突变在氮饥饿时会损害这种蓝细菌中的PHB积累。在本研究中，我们展示了解释所观察到的表型的数据。我们研究了野生型和突变体之间PHB合酶的细胞内定位、代谢以及NADPH库的差异。在sll0783突变体中，PHB合酶的定位未受损；然而，代谢组分析揭示了山梨醇水平的差异，表明其细胞内环境比野生型更具氧化性。我们通过直接测量NADPH/NADP比值以及改变野生型和sll0783突变体的细胞内氧化还原状态来证实这一点。通过使细胞内环境更具还原性，我们能够在生理上弥补PHB合酶活性降低的突变体表型。我们的数据表明，NADPH库是调控PHB生物合成和代谢的一个重要因素，这对于潜在的生物技术应用也具有重要意义。
