Silica cell-wall formation in diatoms is a showcase for the ability of organisms to control inorganic mineralization. The process of silicification by these unicellular algae is tightly regulated within a membrane-bound organelle, the silica deposition vesicle (SDV). Two opposing scenarios were proposed to explain the tight regulation of this intracellular process: a template-mediated process that relies on preformed scaffolds, or a template-independent self-assembly process. The present work points to a third scenario, where the SDV membrane is a dynamic mold that shapes the forming silica. We use in-cell cryo-electron tomography to visualize the silicification process in situ, in its native-state, and with a nanometer-scale resolution. This reveals that the plasma membrane interacts with the SDV membrane via physical tethering at membrane contact sites, where the curvature of the tethered side of the SDV membrane mirrors the intricate silica topography. We propose that silica growth and morphogenesis result from the biophysical properties of the SDV and plasma membranes.

硅藻中二氧化硅细胞壁的形成展示了生物体控制无机矿化的能力。这些单细胞藻类的硅化过程受到膜结合细胞器（二氧化硅沉积囊泡（SDV））的严格调控。提出了两种相反的情况来解释这种细胞内过程的严格调节：依赖于预制支架的模板介导的过程，或独立于模板的自组装过程。目前的工作指出了第三种情况，其中 SDV 膜是一个动态模具，可以塑造正在形成的二氧化硅。我们使用细胞内冷冻电子断层扫描技术以纳米级分辨率原位观察硅化过程的自然状态。这表明质膜通过膜接触位点的物理束缚与 SDV 膜相互作用，其中 SDV 膜的束缚侧的曲率反映了复杂的二氧化硅形貌。我们认为二氧化硅的生长和形态发生是由 SDV 和质膜的生物物理特性引起的。