Cyanophycin Synthesis Optimizes Nitrogen Utilization in the Unicellular Cyanobacterium Synechocystis sp. Strain PCC 6803
Cyanophycin Synthesis Optimizes Nitrogen Utilization in the Unicellular Cyanobacterium Synechocystis sp. Strain PCC 6803
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蓝藻素合成优化单细胞蓝藻集胞藻菌株 PCC 6803 中的氮利用
DOI：
10.1128/aem.01298-18
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发表时间：
2018
影响因子：
4.4
通讯作者：
Forchhammer
中科院分区：
文献类型：
--
作者：
Watzer;Forchhammer
蓝藻素是一种广泛存在于大多数蓝藻和少数异养细菌中的碳氮储存聚合物。它是一种非核糖体多肽，由等摩尔量的天冬氨酸和精氨酸组成。在这里，我们专注于蓝藻素的生理功能和细胞生物学的单细胞非重氮蓝藻集胞藻属。菌株PCC 6803。为了研究蓝藻素合成酶CphA在蓝藻素合成和降解过程中的细胞定位，我们将其与绿色荧光蛋白融合。当CphA失活时，它弥漫地定位于细胞质中。当蓝藻素的合成被触发，CphA首先聚集成灶，后来定位于表面的蓝藻素颗粒。在相应的细胞提取物中，CphA在蓝藻素颗粒表面的定位需要Mg 2+。在蓝藻素降解过程中，CphA从颗粒表面解离并在细胞质中恢复其非活性形式。为了研究蓝藻素的生理作用，我们将野生型细胞与CphA缺陷突变体进行了比较。在标准的实验室条件下，合成蓝藻素的能力并没有赋予生长优势。为了模拟自然栖息地中的情况，在波动和限制的氮补充和/或日/夜循环下培养细胞。在所有这些条件下，蓝藻素提供了一个健身优势，野生型的突变体缺乏蓝藻素。在氮饥饿复苏期间，野生型细胞在夜间积累蓝藻素，并在白天将其用作内部氮源。这表明，蓝藻素可以被用作一个临时的氮存储解偶氮同化从photosynthesis.IMPORTANCEWe澄清了难以捉摸的蓝藻素在nondiazotrophic蓝藻集胞藻属的生物学功能。PCC 6803。蓝藻素是一种动态的碳/氮储存聚合物（多乙酰基-L-聚天冬氨酸），它有条件地存在于大多数蓝藻和少数异养细菌中，作为细胞内含物颗粒。在这里，我们表明，蓝藻素合成酶CphA在非活性状态下定位在细胞质中弥漫。当蓝藻素合成被触发时，活性CphA首先聚集成焦点，然后覆盖成熟蓝藻素颗粒的表面，这在体外需要Mg 2+作为辅因子。蓝藻素的积累使集胞藻能够在氮缺乏的条件下优化氮同化，特别是当氮供应波动和昼夜循环时，通过允许连续的氮同化和储存。因此，在氮供应波动的自然环境中，蓝藻素为野生型蓝藻提供了明显优于非蓝藻素生产细胞的适应性优势。
Cyanophycin is a carbon/nitrogen storage polymer widely distributed in most cyanobacterial strains and in a few heterotrophic bacteria. It is a nonribosomal polypeptide consisting of equimolar amounts of aspartate and arginine. Here, we focused on the physiological function and cell biology of cyanophycin in the unicellular nondiazotrophic cyanobacterium Synechocystis sp. strain PCC 6803. To study the cellular localization of the cyanophycin-synthesizing enzyme CphA during cyanophycin synthesis and degradation, we fused it to green fluorescent protein. When CphA was inactive, it localized diffusely in the cytoplasm. When cyanophycin synthesis was triggered, CphA first aggregated into foci and later localized on the surface of cyanophycin granules. In the corresponding cell extracts, localization of CphA on the cyanophycin granule surface required Mg2+. During cyanophycin degradation, CphA dissociated from the granule surface and returned to its inactive form in the cytoplasm. To investigate the physiological role of cyanophycin, we compared wild-type cells with a CphA-deficient mutant. Under standard laboratory conditions, the ability to synthesize cyanophycin did not confer a growth advantage. To mimic the situation in natural habitats, cells were cultured with a fluctuating and limiting nitrogen supplementation and/or day/night cycles. Under all of these conditions, cyanophycin provided a fitness advantage to the wild type over the mutant lacking cyanophycin. During resuscitation from nitrogen starvation, wild-type cells accumulated cyanophycin during the night and used it as an internal nitrogen source during the day. This demonstrates that cyanophycin can be used as a temporary nitrogen storage to uncouple nitrogen assimilation from photosynthesis.IMPORTANCEWe clarified the elusive biological function of cyanophycin in the nondiazotrophic cyanobacterium Synechocystis sp. PCC 6803. Cyanophycin is a dynamic carbon/nitrogen storage polymer (multi-arginyl-l-polyaspartate) that is conditionally present in most cyanobacteria and a few heterotrophic bacteria as cellular inclusion granules. Here, we show that the cyanophycin-synthesizing enzyme CphA in the nonactive state localizes diffusely in the cytoplasm. When cyanophycin synthesis is triggered, active CphA first aggregates into foci and then covers the surface of mature cyanophycin granules, whichin vitrorequires Mg2+as a cofactor. Cyanophycin accumulation enables Synechocystis sp. to optimize nitrogen assimilation under nitrogen-poor conditions, in particular when the nitrogen supply fluctuates and during day/night cycles, by allowing continuous nitrogen assimilation and storage. Therefore, cyanophycin provides the wild-type cyanobacterium with a clear fitness advantage over non-cyanophycin-producing cells in natural environments with fluctuating nitrogen supply.
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影响因子：
7.4
作者：
Doello, Sofia;Klotz, Alexander;Forchhammer, Karl
通讯作者：
Forchhammer, Karl
影响因子：
9.2
作者：
Klotz, Alexander;Georg, Jens;Forchhammer, Karl
通讯作者：
Forchhammer, Karl
影响因子：
3.6
作者：
Galmozzi, Carla V.;Fernandez-Avila, M. Jesus;Muro-Pastor, M. Isabel
通讯作者：
Muro-Pastor, M. Isabel
影响因子：
4.4
作者：
Elbahloul, Y;Steinbüchel, A
通讯作者：
Steinbüchel, A
影响因子：
6.4
作者：
Watzer B;Engelbrecht A;Hauf W;Stahl M;Maldener I;Forchhammer K
通讯作者：
Forchhammer K