Abstract：
Nitrogen-fixing cyanobacteria not only cause severe blooms but also play an important role in the nitrogen input processes of lakes. The production of extracellular polymeric substances (EPS) and the ability to fix nitrogen from the atmosphere provide nitrogen-fixing cyanobacteria with a competitive advantage over other organisms. Temperature and nitrogen availability are key environmental factors in regulating the growth of cyanobacteria. In this study, Dolichospermum (formerly known as Anabaena) was cultivated at three different temperatures (10 °C, 20 °C, and 30 °C) to examine the impact of temperature and nitrogen availability on nitrogen fixation capacity and the release of EPS. Initially, confocal laser scanning microscopy (CLSM) and the quantification of heterocysts at different temperatures revealed that lower temperatures (10 °C) hindered the differentiation of heterocysts under nitrogen-deprived conditions. Additionally, while heterocysts inhibited the photosynthetic activity of Dolichospermum, the secretion of EPS was notably affected by nitrogen limitation, particularly at 30 °C. Finally, real-time quantitative polymerase chain reaction (qPCR) was used to measure the expression of nitrogen-utilizing genes (ntcA and nifH) and EPS synthesis-related genes (wzb and wzc). The results indicated that under nitrogen-deprived conditions, the expression of each gene was upregulated, and there was a significant correlation between the upregulation of nitrogen-utilizing and EPS synthesis genes (P < 0.05). Our findings suggested that Dolichospermum responded to temperature variation by affecting the formation of heterocysts, impacting its potential nitrogen fixation capacity. Furthermore, the quantity of EPS released was more influenced by nitrogen availability than temperature. This research enhances our comprehension of interconnections between nitrogen deprivation and EPS production under the different temperatures.
摘要：
固氮蓝藻不仅引起严重的水华，而且在湖泊的氮输入过程中起着重要作用。胞外聚合物（EPS）的产生和从大气中固定氮的能力为固氮蓝细菌提供了与其他生物相比具有竞争优势的优势。温度和氮有效性是调节蓝藻生长的关键环境因素。在这项研究中,在三种不同的温度（10°C，20°C,和30°C），以检查温度和氮有效性对固氮能力和EPS释放的影响。最初，共聚焦激光扫描显微镜（CLSM）和不同温度下杂环的定量表明，较低的温度（10°C）阻碍了氮剥夺条件下杂环的分化。此外,异形子抑制了Dolichospermum的光合活性，EPS的分泌受到氮限制的显著影响，特别是在30°C最后,实时定量聚合酶链反应（qPCR）用于测量氮利用基因（ntcA和nifH）和EPS合成相关基因（wzb和wzc）的表达。结果表明，在氮剥夺条件下，每个基因的表达上调，利用氮基因与EPS合成基因的上调存在显著相关性(P<0.05)。我们的发现表明，Dolichospermum通过影响异晶的形成来响应温度变化，影响其潜在的固氮能力。此外，EPS释放量受氮有效性的影响大于温度。这项研究增强了我们对不同温度下氮剥夺与EPS生产之间相互关系的理解。
