A Specific Glycogen Mobilization Strategy Enables Rapid Awakening of Dormant Cyanobacteria from Chlorosis
A Specific Glycogen Mobilization Strategy Enables Rapid Awakening of Dormant Cyanobacteria from Chlorosis
复制标题
DOI：
10.1104/pp.18.00297
复制
发表时间：
2018-06-01
期刊：
影响因子：
7.4
通讯作者：
Forchhammer, Karl
中科院分区：
文献类型：
--
作者：
Doello, Sofia;Klotz, Alexander;Forchhammer, Karl
许多生物体通过进入休眠状态来生存在压力条件下，当应激源消失时，休眠状态可以迅速退出；这种能力提供了强大的选择性优势。在蓝藻聚胞藻中发现。PCC 6803，氮黄化的结束时间不到48小时，这是因为这些蓝藻具有令人印象深刻的代谢灵活性，在重新进入光自养生长之前，它们经历了异养和混合营养阶段。在这些状态之间切换需要碳水化合物氧化、二氧化碳固定和光合作用的微妙协调。在这里，我们通过评估不同碳分解代谢途径的突变体在氮黄化和复苏过程中的作用来研究这些途径的贡献。将硝酸盐添加到氮饥饿的细胞中，迅速启动了唤醒程序。代谢从维持代谢，其特征是残留的光合作用和低的细胞ATP水平，到最初的异养阶段，特征是呼吸作用和ATP水平的立即增加。这种呼吸作用依赖于糖原磷酸化酶GlgP2催化的糖原分解。在随后的短暂混合营养阶段，光合作用和CO2固定重新开始，糖原被消耗。在混合营养阶段，需要并行运行氧化戊糖磷酸循环和Entner-Doudoroff途径才能进行复苏；通过Embden-Meyerhof-Parns途径的糖酵解途径并不重要。我们的数据表明，在复苏过程中，只有Entner-Doudoroff和氧化戊糖磷酸途径提供重建营养细胞所需的合成代谢反应所需的代谢中间产物。有趣的是，糖原分解代谢的关键酶已经在之前的褪绿阶段表达，显然是为快速复苏做准备。
Many organisms survive stressful conditions via entry into a dormant state that can be rapidly exited when the stressor disappears; this ability provides a strong selective advantage. In the cyanobacterium Synechocystis sp. PCC 6803, the exit from nitrogen chlorosis takes less than 48 h and is enabled by the impressive metabolic flexibility of these cyanobacteria, which pass through heterotrophic and mixotrophic phases before reentering photoautotrophic growth. Switching between these states requires delicate coordination of carbohydrate oxidation, CO2 fixation, and photosynthesis. Here, we investigated the contribution of the different carbon catabolic routes by assessing mutants of these pathways during nitrogen chlorosis and resuscitation. The addition of nitrate to nitrogen-starved cells rapidly starts the awakening program. Metabolism switches from maintenance metabolism, characterized by residual photosynthesis and low cellular ATP levels, to an initial heterotrophic phase, characterized by respiration and an immediate increase in ATP levels. This respiration relies on glycogen breakdown catalyzed by the glycogen phosphorylase GlgP2. In the following transient mixotrophic phase, photosynthesis and CO2 fixation restart and glycogen is consumed. During the mixotrophic phase, parallel operation of the oxidative pentose phosphate cycle and the Entner-Doudoroff pathway is required for resuscitation to proceed; the glycolytic route via the Embden-Meyerhof-Parnas pathway has minor importance. Our data suggest that, during resuscitation, only the Entner-Doudoroff and oxidative pentose phosphate pathways supply the metabolic intermediates necessary for the anabolic reactions required to reconstitute a vegetative cell. Intriguingly, the key enzymes for glycogen catabolism are already expressed during the preceding chlorotic phase, in apparent preparation for rapid resuscitation.