ABSTRACT: The toxic cyanobacterium Nodularia spumigena regularly forms large surface blooms in the central Baltic Sea during the summer period. Bloom formation occurs when the water body is virtually free of the nutrients nitrate and phosphate. The capacity of Nodularia spp. for nitrogen fixation makes it independent from combined nitrogen sources; however, its adaptation to low phosphate levels is poorly investigated. We compared the behaviour of N. spumigena strain CCY9414 under high- and low-phosphate conditions in the laboratory. Cells cultivated under P-limited conditions showed no growth but higher expression of pho regulon genes, such as pstS, which are known to respond to P-starvation. However, electron microscopy showed a massive accumulation of polyphosphate granules in long-term P-starved cells and not in those grown in P-containing medium. The polyphosphate nature of the black granules was verified by electron energy-loss spectroscopy and subsequently by polyphosphate quantification in Nodularia cells. Polyphosphate accumulation was also observed in cells of Aphanizomenon flos-aquae obtained from a summer bloom, where only traces of phosphate were available in the surrounding water body. These findings indicate that bloom-forming cyanobacteria prefer to store the traces of available phosphate in the form of polyphosphates, instead of using it for further growth. This strategy could help in competition with other microorganisms for phosphate during bloom conditions, whilst allowing rapid cell division upon more favourable phosphate concentrations.

中文翻译：

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蓝藻根瘤菌菌株CCY9414在长期P限制条件下积累多磷酸盐

摘要：在夏季，有毒的蓝藻结节藻定期在波罗的海中部形成大面积的水华。当水体中几乎没有营养物硝酸盐和磷酸盐时，就会形成水华。结节菌的能力。用于固氮，使其独立于组合氮源；然而，其对低磷酸盐水平的适应性研究很少。我们比较的行为N. spumigena应变CCY9414在实验室高，低磷酸盐条件下。在P限制条件下培养的细胞没有生长，但是pho regulon基因（例如pstS）的表达更高，已知对P饥饿有反应。但是，电子显微镜显示在长期缺乏P的细胞中而不是在含P的培养基中生长的细胞中大量积累了多磷酸盐颗粒。黑色颗粒的多磷酸盐性质通过电子能量损失光谱法进行了验证，随后通过结节瘤细胞中的多磷酸盐定量进行了验证。还在浮游水藻的细胞中观察到了多磷酸盐的积累从夏季花期获得，周围的水体中只有微量的磷酸盐。这些发现表明，形成花白的蓝细菌更喜欢以多磷酸盐的形式存储痕量的可用磷酸盐，而不是将其用于进一步的生长。这种策略可以帮助在开花条件下与其他微生物竞争磷酸盐，同时在更有利的磷酸盐浓度下实现快速细胞分裂。