Abstract：
Excess of selenium (Se) in aquatic ecosystems has necessitated thorough investigations into the effects/consequences of this metalloid on the autochthonous organisms exposed to it. The molecular details of Se-mediated adaptive response remain unknown in cyanobacteria. This study aims to uncover the molecular mechanisms driving the divergent physiological responses of cyanobacteria on exposure to selenate [Se(VI)] or selenite [Se(IV)], the two major water-soluble oxyanions of Se. The cyanobacterium, Anabaena PCC 7120, withstood 0.4 mM of Se(VI), whereas even 0.1 mM of Se(IV) was detrimental, affecting photosynthesis and enhancing endogenous ROS. Surprisingly, Anabaena pre-treated with Se(VI), but not Se(IV), showed increased tolerance to oxidative stress mediated by H2O2/methyl viologen. RNA-Seq analysis showed Se(VI) to elevate transcription of genes encoding anti-oxidant proteins and Fe-S cluster biogenesis, whereas the photosynthesis-associated genes, which were mainly downregulated by Se(IV), remained unaffected. Specifically, the content of typical 2-Cys-Prx (Alr4641), a redox-maintaining protein in Anabaena, was elevated with Se(VI). In comparison to the wild-type, the Anabaena strain over-expressing the Alr4641 protein (An4641+) showed enhanced tolerance to Se(VI) stress, whereas the corresponding knockdown-strain (KD4641) was sensitive to this stressor. Incidentally, among these strains, only An4641+ was better protected from the ROS-mediated damage caused by high dose of Se(VI). These results suggest that altering the content of the antioxidant protein 2-Cys-Prx, could be a potential strategy for modulating resistance to selenate. Thus, involvement of oxidative stress machinery appears to be the major determinant, responsible for the contrasting physiological differences observed in response to selenate/selenite in cyanobacteria.
摘要：
水生生态系统中硒（Se）过量，因此有必要对这种准金属对暴露于其的本地生物的影响/后果进行彻底调查。硒介导的适应性反应的分子细节在蓝细菌中仍然未知。本研究旨在揭示蓝细菌暴露于硒酸盐[Se（VI）]或硒酸盐[Se（IV）]时产生不同生理反应的分子机制。硒的两种主要水溶性氧阴离子。蓝细菌,鱼腥草PCC7120，耐受0.4mMSe（VI），即使0.1mM的Se（IV）也是有害的，影响光合作用和增强内源性ROS。令人惊讶的是,用Se（VI）预处理的鱼腥草，但不是Se（IV），显示对H2O2/甲基紫精介导的氧化应激的耐受性增加。RNA-Seq分析表明Se（VI）可以提高编码抗氧化蛋白和Fe-S簇生物发生的基因的转录，而与光合作用相关的基因，主要受Se(IV)下调，未受影响。具体来说,典型2-Cys-Prx(Alr4641)的含量，鱼腥草中的一种氧化还原维持蛋白，用Se(VI)升高。与野生型相比，Anabaena菌株过表达Alr4641蛋白（An4641）显示出对Se（VI）胁迫的增强耐受性，而相应的敲低应变（KD4641）对该应激源敏感。顺便说一句,在这些菌株中，只有An4641+能更好地保护高剂量Se(VI)引起的ROS介导的损伤。这些结果表明，改变抗氧化蛋白2-Cys-Prx的含量，可能是调节硒酸盐抗性的潜在策略。因此，氧化应激机制的参与似乎是主要的决定因素，负责在蓝细菌中对硒酸盐/亚硒酸盐的反应中观察到的对比生理差异。
