Centre Algatech, Opatovický mlýn, Institute of Microbiology, The Czech Academy of Sciences, Třeboň, 379 01 Czech Republic.
Environ Microbiol. 2018 Feb;20(2):546-560. doi: 10.1111/1462-2920.13963. Epub 2018 Jan 4.
The oceanic unicellular diazotrophic cyanobacterium Crocosphaera watsonii WH8501 exhibits large diel changes in abundance of both Photosystem II (PSII) and Photosystem I (PSI). To understand the mechanisms underlying these dynamics, we assessed photosynthetic parameters, photosystem abundance and composition, and chlorophyll-protein biosynthesis over a diel cycle. Our data show that the decline in PSII activity and abundance observed during the dark period was related to a light-induced modification of PSII, which, in combination with the suppressed synthesis of membrane proteins, resulted in monomerization and gradual disassembly of a large portion of PSII core complexes. In the remaining population of assembled PSII monomeric complexes, we detected the non-functional version of the D1 protein, rD1, which was absent in PSII during the light phase. During the dark period, we also observed a significant decoupling of phycobilisomes from PSII and a decline in the chlorophyll a quota, which matched the complete loss of functional PSIIs and a substantial decrease in PSI abundance. However, the remaining PSI complexes maintained their photochemical activity. Thus, during the nocturnal period of nitrogen fixation C. watsonii operates a suite of regulatory mechanisms for efficient utilization/recycling of cellular resources and protection of the nitrogenase enzyme.
海洋单细胞固氮蓝藻 Crocosphaera watsonii WH8501 的光合作用系统 II（PSII）和光合作用系统 I（PSI）的丰度均呈现出较大的昼夜变化。为了了解这些动态变化的机制，我们在昼夜周期内评估了光合作用参数、光系统丰度和组成以及叶绿素-蛋白生物合成。我们的数据表明，在黑暗期观察到的 PSII 活性和丰度下降与 PSII 的光诱导修饰有关，这种修饰与膜蛋白合成的抑制相结合，导致 PSII 核心复合物的大部分发生单体化和逐渐解体。在剩余的组装 PSII 单体复合物中，我们检测到 D1 蛋白的非功能性版本 rD1，它在光照阶段不存在于 PSII 中。在黑暗期，我们还观察到藻胆体与 PSII 的显著解偶联以及叶绿素 a 配额的下降，这与功能 PSII 的完全丧失和 PSI 丰度的大幅下降相匹配。然而，剩余的 PSI 复合物保持其光化学活性。因此，在固氮的夜间阶段，C. watsonii 采用了一系列调节机制来有效利用/回收细胞资源并保护固氮酶。
