Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, USA.
Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA.
Harmful Algae. 2017 Sep;68:258-270. doi: 10.1016/j.hal.2017.07.001. Epub 2017 Sep 6.
The marine eukaryotic alga Heterosigma akashiwo (Raphidophyceae) is known for forming ichthyotoxic harmful algal blooms (HABs). In the past 50 years, H. akashiwo blooms have increased, occurring globally in highly eutrophic coastal and estuarine systems. These systems often incur dramatic physicochemical changes, including macronutrient (nitrogen and phosphorus) enrichment and depletion, on short timescales. Here, H. akashiwo cultures grown under nutrient replete, low N and low P growth conditions were examined for changes in biochemical and physiological characteristics in concert with transcriptome sequencing to provide a mechanistic perspective on the metabolic processes involved in responding to N and P stress. There was a marked difference in the overall transcriptional pattern between low N and low P transcriptomes. Both nutrient stresses led to significant changes in the abundance of thousands of contigs related to a wide diversity of metabolic pathways, with limited overlap between the transcriptomic responses to low N and low P. Enriched contigs under low N included many related to nitrogen metabolism, acquisition, and transport. In addition, metabolic modules like photosynthesis and carbohydrate metabolism changed significantly under low N, coincident with treatment-specific changes in photosynthetic efficiency and particulate carbohydrate content. P-specific contigs responsible for P transport and organic P use were more enriched in the low P treatment than in the replete control and low N treatment. These results provide new insight into the genetic mechanisms that distinguish how this HAB species responds to these two common nutrient stresses, and the results can inform future field studies, linking transcriptional patterns to the physiological ecology of H. akashiwo in situ.
海洋真核藻类塔玛亚历山大藻（红藻门）以形成鱼毒性有害藻华（HAB）而闻名。在过去的 50 年中，塔玛亚历山大藻的爆发有所增加，在富营养化的沿海和河口系统中全球范围内都有发生。这些系统经常在短时间内发生剧烈的物理化学变化，包括大量营养物（氮和磷）的富集和耗尽。在这里，研究了在营养充足、低 N 和低 P 生长条件下培养的塔玛亚历山大藻培养物的生化和生理特性变化，并进行了转录组测序，以提供对参与应对 N 和 P 胁迫的代谢过程的机制视角。低 N 和低 P 转录组之间的整体转录模式存在明显差异。两种养分胁迫都导致与广泛代谢途径相关的数千个连续序列的丰度发生显著变化，低 N 和低 P 对转录组的响应之间重叠有限。低 N 下富集的连续序列包括许多与氮代谢、获取和运输有关的序列。此外，光合作用和碳水化合物代谢等代谢模块在低 N 下也发生了显著变化，与特定于处理的光合作用效率和颗粒状碳水化合物含量的变化一致。负责 P 运输和有机 P 使用的低 P 特异性连续序列在低 P 处理中比在充足对照和低 N 处理中更为丰富。这些结果为区分这种 HAB 物种如何应对这两种常见养分胁迫的遗传机制提供了新的见解，并为未来的现场研究提供了信息，将转录模式与塔玛亚历山大藻的生理生态学联系起来。
