Resting stages are reported for several unicellular eukaryotes including diatoms that can produce spores or resting cells. These stages represent a repository of diversity in sediments but the factors that induce their formation are elusive. We investigated spore formation in the marine diatom Chaetoceros socialis. Our results confirm that nitrogen starvation is an effective experimental trigger for spore formation. However, we observed that spores are also produced when the external pool of nutrients is not limiting, and by using a semicontinuous setup, we could show that they appear only when cell density is high. The presence of a chemical cue mediating spore formation was supported by experiments carried out incubating cells with culture media conditioned by both healthy and lysed cells. These findings shed new light on the mechanisms that regulate the transition between life cycle stages and represent an experimental baseline for the identification of the signaling molecules.

中文翻译：

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依赖密度的机制调节硅藻Chaetoceros socialis中孢子的形成

报道了几种单细胞真核生物的静止阶段，包括可以产生孢子或静止细胞的硅藻。这些阶段代表了沉积物多样性的储存库，但是导致其形成的因素却难以捉摸。我们调查了海洋硅藻Chaetoceros socialis中孢子的形成。我们的结果证实，氮饥饿是孢子形成的有效实验触发因素。但是，我们观察到当外部养分池不受限制时也会产生孢子，通过使用半连续设置，我们可以证明孢子仅在细胞密度高时才会出现。通过用健康和裂解细胞调节的培养基培养细胞进行的实验支持了介导孢子形成的化学提示的存在。这些发现为调节生命周期阶段之间的过渡的机制提供了新的思路，并代表了鉴定信号分子的实验基准。