Jang Se Hyeon, Lin YuanYu, Marchetti Adrian
Department of Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill 27514, NC, United States.
Department of Oceanography, Chonnam National University, Gwangju 61186, Republic of Korea.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wraf099.
The availability of the micronutrient iron is important in regulating phytoplankton growth across much of the world's oceans, particularly in the high-nutrient, low-chlorophyll regions. Compared to known mechanisms of iron acquisition and conservation in autotrophic protists (e.g. diatoms), those of dinoflagellates remain unclear, despite their frequent presence in offshore iron-limited waters. Here, we investigate the strategies of an ecologically important mixotrophic dinoflagellate to coping with low iron conditions. Coupled gene expression and physiological responses as a function of iron availability were examined in oceanic and coastal strains of the dinoflagellate Karlodinium. Under iron-replete conditions, grazing was only detected in coastal variants, resulting in faster growth rates compared to when grown autotrophically. Under iron-limited conditions, all isolates exhibited slower growth rates, reduced photosynthetic efficiencies, and lower cellular iron quotas than in iron-replete conditions. However, oceanic isolates exhibited higher relative growth rates compared to coastal isolates under similar low iron concentrations, suggesting they are better adapted to coping under iron limitation. Yet the oceanic isolates did not exhibit the ability to appreciably reduce cell volume or increase iron-use efficiencies compared to the coastal isolates to cope with iron limitation, as often observed in oceanic diatoms. Rather, molecular pathway analysis and corresponding gene expression patterns suggest that oceanic Karlodinium utilizes a high-affinity iron uptake system when iron is low. Our findings reveal cellular mechanisms by which dinoflagellates have adapted to low iron conditions, further shedding light on how they potentially survive in variable iron regions of the world's oceans.
在世界大部分海洋中，微量营养素铁的可利用性对于调节浮游植物的生长至关重要，尤其是在高营养、低叶绿素区域。与自养原生生物（如硅藻）中已知的铁获取和保存机制相比，尽管甲藻经常出现在近海铁限制水域，但它们的机制仍不清楚。在这里，我们研究了一种具有重要生态意义的混合营养甲藻应对低铁条件的策略。我们在海洋和沿海的卡尔藻株系中研究了基因表达与生理反应随铁可利用性的变化情况。在铁充足的条件下，仅在沿海变种中检测到摄食现象，与自养生长时相比，其生长速度更快。在铁限制条件下，所有分离株的生长速度都比铁充足条件下慢，光合效率降低，细胞铁配额也更低。然而，在相似的低铁浓度下，海洋分离株的相对生长速度高于沿海分离株，这表明它们更能适应在铁限制条件下生存。然而，与沿海分离株相比，海洋分离株在应对铁限制时，并没有表现出明显减小细胞体积或提高铁利用效率的能力，而这在海洋硅藻中经常可以观察到。相反，分子途径分析和相应的基因表达模式表明，海洋卡尔藻在铁含量低时利用高亲和力的铁摄取系统。我们的研究结果揭示了甲藻适应低铁条件的细胞机制，进一步阐明了它们在世界海洋中铁含量多变的区域可能的生存方式。
