ABSTRACT Planktonic diatoms thrive in the water column, and several species can transform into resting stages – spores or resting cells – that sink to the bottom of the sea. Resting stages are generally produced when environmental conditions are not optimal for growth and can remain viable in sediments for a long time. We tested different aspects related to the formation of spores in Chaetoceros socialis, one of the dominant diatoms in the Gulf of Naples (Mediterranean Sea, Italy). Observations in time lapse and confocal laser scanning microscopy allowed illustration of the formation of endogenous spores, in which valve deposition is accompanied by an acytokinetic nuclear division. The complete transition from vegetative cell to spore takes about 8–10 h and, if exposed to the light, spores can germinate again after a few days. The depletion of nitrogen source in the culture medium induced the formation of spores, with very similar dynamics among different sympatric strains; extremely high percentages of spores (up to >95%) were produced after 4–5 days. Once formed, spores can remain viable for up to nine months, and anoxic conditions favour their preservation. Identical dynamics of spore formation were detected in freshly established cultures and in cultures produced by the germination of spores kept dormant for different lengths of time. Our results suggest that spores of C. socialis can, in principle, rapidly shift between vegetative cells and resting stages that may explain the success of this species in coastal water. Our results also demonstrate that storage of resting spores may represent an alternative to cryopreservation.

中文翻译：

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硅藻 Chaetoceros socialis：孢子形成和保存

摘要 浮游硅藻在水体中茁壮成长，一些物种可以转变为沉入海底的静止阶段——孢子或静止细胞。当环境条件不适合生长并且可以在沉积物中长时间保持活力时，通常会产生静止阶段。我们测试了与 Chaetoceros socialis 孢子形成相关的不同方面，Chaetoceros socialis 是那不勒斯湾（意大利地中海）的主要硅藻之一。时间推移和共聚焦激光扫描显微镜的观察可以说明内源性孢子的形成，其中瓣膜沉积伴随着细胞动力学核分裂。从营养细胞到孢子的完全转变大约需要 8-10 小时，如果暴露在光线下，几天后孢子可以再次发芽。培养基中氮源的消耗诱导孢子的形成，不同同域菌株之间的动力学非常相似；4-5 天后产生了极高百分比的孢子（高达 >95%）。一旦形成，孢子可以存活长达九个月，缺氧条件有利于它们的保存。在新建立的培养物和通过休眠不同时间长度的孢子萌发产生的培养物中检测到相同的孢子形成动力学。我们的结果表明，C. socialis 的孢子原则上可以在营养细胞和休眠阶段之间快速转换，这可能解释了该物种在沿海水域中的成功。我们的结果还表明，静止孢子的储存可能代表了冷冻保存的替代方法。