Ocean and Earth Science, University of Southampton, Southampton, SO14 3ZH, UK.
National Oceanography Centre, Southampton, SO14 3ZH, UK.
ISME J. 2022 Apr;16(4):1055-1064. doi: 10.1038/s41396-021-01151-1. Epub 2021 Nov 24.
The filamentous diazotrophic cyanobacterium Trichodesmium is responsible for a significant fraction of marine di-nitrogen (N) fixation. Growth and distribution of Trichodesmium and other diazotrophs in the vast oligotrophic subtropical gyres is influenced by iron (Fe) and phosphorus (P) availability, while reciprocally influencing the biogeochemistry of these nutrients. Here we use observations across natural inverse gradients in Fe and P in the North Atlantic subtropical gyre (NASG) to demonstrate how Trichodesmium acclimates in situ to resource availability. Transcriptomic analysis identified progressive upregulation of known iron-stress biomarker genes with decreasing Fe availability, and progressive upregulation of genes involved in the acquisition of diverse P sources with decreasing P availability, while genes involved in N fixation were upregulated at the intersection under moderate Fe and P availability. Enhanced N fixation within the Fe and P co-stressed transition region was also associated with a distinct, consistent metabolic profile, including the expression of alternative photosynthetic pathways that potentially facilitate ATP generation required for N fixation with reduced net oxygen production. The observed response of Trichodesmium to availability of both Fe and P supports suggestions that these biogeochemically significant organisms employ unique molecular, and thus physiological responses as adaptations to specifically exploit the Fe and P co-limited niche they construct.
丝状固氮蓝藻束毛藻负责海洋双氮 (N) 固定的很大一部分。束毛藻和其他固氮生物在广阔的贫营养亚热带环流中的生长和分布受铁 (Fe) 和磷 (P) 可用性的影响，同时反过来影响这些养分的生物地球化学。在这里，我们使用北大西洋亚热带环流 (NASG) 中 Fe 和 P 的自然反梯度的观测结果来证明束毛藻如何在现场适应资源可用性。转录组分析确定了随着 Fe 可用性的降低，已知铁胁迫生物标志物基因的逐步上调，以及随着 P 可用性的降低，参与获取各种 P 源的基因的逐步上调，而与 N 固定有关的基因在中等 Fe 和 P 可用性的交叉点上调。在 Fe 和 P 共同胁迫过渡区域内增强的 N 固定也与独特、一致的代谢特征相关联，包括替代光合作用途径的表达，这些途径可能有助于在减少净氧气产生的情况下生成固定 N 所需的 ATP。束毛藻对 Fe 和 P 可用性的观察到的反应支持了这样的观点，即这些具有重要生物地球化学意义的生物体采用独特的分子，从而是生理反应，作为对它们所构建的 Fe 和 P 共同限制生态位的特殊利用的适应。
