Iron uptake by diatoms is a biochemical process with global biogeochemical implications. In large regions of the surface ocean diatoms are both responsible for the majority of primary production and frequently experiencing iron limitation of growth. The strategies used by these phytoplankton to extract iron from seawater constrain carbon flux into higher trophic levels and sequestration into sediments. In this study we use reverse genetic techniques to target putative iron-acquisition genes in the model pennate diatom Phaeodactylum tricornutum We describe components of a reduction-dependent siderophore acquisition pathway that relies on a bacterial-derived receptor protein and provides a viable alternative to inorganic iron uptake under certain conditions. This form of iron uptake entails a close association between diatoms and siderophore-producing organisms during low-iron conditions. Homologs of these proteins are found distributed across diatom lineages, suggesting the significance of siderophore utilization by diatoms in the marine environment. Evaluation of specific proteins enables us to confirm independent iron-acquisition pathways in diatoms and characterize their preferred substrates. These findings refine our mechanistic understanding of the multiple iron-uptake systems used by diatoms and help us better predict the influence of iron speciation on taxa-specific iron bioavailability.

译文

硅藻对铁的吸收是一个具有全球生物地球化学意义的生物化学过程。在地表的大区域中,硅藻既负责大部分初级生产,又经常遇到铁的生长限制。这些浮游植物从海水中提取铁所使用的策略将碳通量限制在较高的营养水平并封存到沉积物中。在这项研究中,我们使用反向遗传学技术靶向模型中的戊二烯硅藻Phaeodactylum tricornutum中假定的铁捕获基因。我们描述了依赖于细菌的受体蛋白的还原依赖性铁载体获得途径的组成部分,并为无机铁提供了可行的替代方法在一定条件下的摄取。在低铁条件下,这种形式的铁吸收需要硅藻和产生铁载体的生物之间的紧密联系。发现这些蛋白质的同系物分布在整个硅藻谱系中,表明在海洋环境中硅藻利用铁载体具有重要意义。对特定蛋白质的评估使我们能够确认硅藻中独立的铁捕获途径并表征其优选的底物。这些发现完善了我们对硅藻使用的多种铁吸收系统的机械理解,并有助于我们更好地预测铁形态对生物分类特异性铁生物利用度的影响。

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