Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany.
Department of Biology, Botanical Institute, Christian-Albrechts-University, 24118 Kiel, Germany.
Int J Mol Sci. 2019 Apr 20;20(8):1942. doi: 10.3390/ijms20081942.
Polyhydroxybutyrate (PHB) is a polymer of great interest as a substitute for conventional plastics, which are becoming an enormous environmental problem. PHB can be produced directly from CO in photoautotrophic cyanobacteria. The model cyanobacterium sp. PCC 6803 produces PHB under conditions of nitrogen starvation. However, it is so far unclear which metabolic pathways provide the precursor molecules for PHB synthesis during nitrogen starvation. In this study, we investigated if PHB could be derived from the main intracellular carbon pool, glycogen. A mutant of the major glycogen phosphorylase, GlgP2 ( product), was almost completely impaired in PHB synthesis. Conversely, in the absence of glycogen synthase GlgA1 ( product), cells not only produced less PHB, but were also impaired in acclimation to nitrogen depletion. To analyze the role of the various carbon catabolic pathways (EMP, ED and OPP pathways) for PHB production, mutants of key enzymes of these pathways were analyzed, showing different impact on PHB synthesis. Together, this study clearly indicates that PHB in glycogen-producing sp. PCC 6803 cells is produced from this carbon-pool during nitrogen starvation periods. This knowledge can be used for metabolic engineering to get closer to the overall goal of a sustainable, carbon-neutral bioplastic production.
聚羟基丁酸酯（PHB）作为传统塑料的替代品，具有很大的研究价值，因为传统塑料正逐渐成为一个严重的环境问题。PHB 可以直接由光自养蓝细菌中的 CO 产生。模式蓝藻 sp. PCC 6803 在氮饥饿条件下产生 PHB。然而，目前尚不清楚在氮饥饿期间，哪些代谢途径为 PHB 合成提供前体分子。在这项研究中，我们研究了 PHB 是否可以来自主要的细胞内碳库——糖原。主要糖原磷酸化酶 GlgP2（产物）的突变体几乎完全不能合成 PHB。相反，在没有糖原合酶 GlgA1（产物）的情况下，细胞不仅产生的 PHB 较少，而且对氮饥饿的适应能力也受损。为了分析各种碳分解代谢途径（EMP、ED 和 OPP 途径）对 PHB 生产的作用，分析了这些途径中关键酶的突变体，结果表明它们对 PHB 合成的影响不同。总的来说，这项研究清楚地表明，在产生糖原的 sp. PCC 6803 细胞中，PHB 是在氮饥饿期间由这个碳库产生的。这一知识可用于代谢工程，以更接近可持续、碳中和生物塑料生产的总体目标。
