基于转录组分析夜光藻氮、磷代谢机制及其与赤潮过程的关系

Noctiluca scintillans (Noctiluca) is an important cosmopolitan red-tide forming heterotrophic dinoflagellate. It contains large amount of ammonium and phosphate in cell, which can supply nutrients for its algal food during mid- to late-bloom stage and, hence, prolong the bloom. Meanwhile, its nitrogen and phosphorus metabolism might also affect the way it reproduces (meiosis or mitosis). However, it is still unclear the accumulation mechanism and autecological importance of these dissolved inorganic contents in Noctiluca. Its nitrogen and phosphorus metabolism during bloom and their relationship with the bloom development also remain unknown. Our studies have showed that algal food quality has great influence on the growth, grazing and metabolic rates of Noctiluca, but it is able to differentially allocate nitrogen and phosphorus to organic and inorganic pools to maintain its overall homeostasis. Such environmental adaptability may help it maintain the bloom. Therefore, in this project, we will further conduct field survey to trace the bloom, and laboratory experiment to mimic its feeding on different quality food. By combining both traditional ecological methods and more recent transcriptome sequencing analysis, we will investigate the response of the nitrogen and phosphorus metabolism of Noctiluca to the changing food environment and other environmental factors during the bloom. We will focus on the influence of food quality on these pathways，and its relationship with the bloom development. This project can help understand Noctilcua’s environmental adaptability, and the mechanism of its bloom formation, development and decline.

夜光藻是全球广布的异养型赤潮甲藻。其胞内含有丰富的氨氮和磷酸盐，赤潮中后期可作为饵料藻的营养盐补充，从而维持自身赤潮的延续。同时，夜光藻的氮、磷代谢也可能与其增殖方式（有丝分裂和减数分裂）有密切关系。但目前对于夜光藻胞内无机氮、磷的产生途径和生理生化意义，以及相关代谢机制与赤潮过程的关系尚不清楚。初步研究表明，夜光藻的生长、摄食和代谢速率会受食物营养质量的影响，但它可通过调节有机和无机部分的氮、磷来保持整体稳态，增强其环境适应性，有助于赤潮维持。基于此，本项目拟综合传统生态学和转录组学的研究方法，通过现场跟踪夜光藻赤潮，以及室内模拟其对不同营养质量饵料藻的摄食，从转录层面分析夜光藻的氮、磷代谢在赤潮过程中对食物和环境因子扰动的响应，并重点关注食物营养质量对夜光藻氮、磷代谢的影响，解析其与赤潮过程的关系。本项目可为深入了解夜光藻的环境适应性，及其赤潮发生、发展和消亡的生物学机制提供依据。

夜光藻是全球广布的异养型赤潮甲藻，其胞内含有丰富的无机氨氮和磷酸盐，赤潮中后期可作为浮游植物的营养盐补充，从而维持自身赤潮的延续。同时，夜光藻的氮、磷代谢也可能与其营养状态及增殖方式有密切关系。但对于夜光藻如何调整细胞营养代谢以应对食物种群组成、数量和质量的变化，目前尚不清楚。基于此，本项目综合利用传统生态学和分子生物学的研究方法，开展了一系赤潮现场观测、实验室生理实验及高通量测序，以期阐明夜光藻营养代谢机制。.研究结果表明：1）夜光藻的摄食有一定的选择性，且主要以硅藻和甲藻为食，但在赤潮高峰期，夜光藻亦会摄食微微型真核生物，以维持其生长的需求；2）赤潮中、后期，夜光藻处于营养限制状态，且磷限制较为严重；在该阶段，夜光藻的营养代谢能力有一定降低，但主要的碳、氮代谢途径仍较为活跃，然而其摄食消化能力减弱，生长受限；3）室内研究进一步表明，摄食缺氮饵料藻时，夜光藻会提高其摄食能力以提高氮的利用，满足其生长的需求；而摄食缺磷饵料藻会影响其摄食、运动能力，虽然夜光藻会提高其对有机磷的利用以满足生长对磷的需求，但由于磷源严重不足，其生长仍受到严重的影响。因此，磷缺乏可能是夜光藻赤潮消亡的重要生物学原因。此外，夜光藻共附生细菌亦可能在其营养代谢过程中发挥重要作用，影响其赤潮进程。.本项目研究成果有助于揭示赤潮过程中夜光藻对环境和食物扰动的应答代谢特征和分子机制，为阐明夜光藻的环境适应性、及其赤潮发生、发展和消亡的生物学机制奠定基础。