Ganser Maximilian H, Weißenbacher Birgit, Agatha Sabine
Department of Environment and Biodiversity, University of Salzburg, Salzburg, Austria.
J Eukaryot Microbiol. 2025 Jul-Aug;72(4):e70025. doi: 10.1111/jeu.70025.
Tintinnid ciliates are distinguished by their loricae (shells), the key synapomorphy of these mainly marine planktonic protists. They can divide daily, with a considerable portion of biomass stored in the loricae. During each division, lorica-forming material (LFM) is produced and afterwards used by the proter (anterior division product) to construct a new lorica, while the opisthe (posterior division product) retains the parental one. Many aspects of lorica formation remain unclear, and no study describes the entire process from material maturation via secretion to assembly. Here, we present the first thorough investigation at cellular and sub-cellular levels, employing light microscopy on dividers and postdividers, as well as transmission electron microscopy on primarily cryofixed specimens from a Schmidingerella culture. Our study reconstructs LFM maturation, identifying two main developmental stages: the morula-shaped precursor granules and the mature granules. The latter cluster in the proter's ventral portion with a peripheral longitudinal strip of small granules embedded in large ones. Ultrastructurally and chemically, the mature granules of both size classes are identical. Through detailed live observations, we followed and documented, for the first time, the process of cell division, the behavior of the proter, the release of LFM granules, and features of lorica formation.
钟形虫类纤毛虫以其外壳（鞘）为特征，这是这些主要生活在海洋中的浮游原生生物的关键共衍征。它们每天都能分裂，相当一部分生物量储存在外壳中。在每次分裂过程中，会产生外壳形成物质（LFM），随后前仔虫（前部分裂产物）利用它构建一个新的外壳，而后仔虫（后部分裂产物）则保留亲代的外壳。外壳形成的许多方面仍不清楚，也没有研究描述从物质成熟到分泌再到组装的整个过程。在这里，我们首次在细胞和亚细胞水平上进行了全面研究，对正在分裂的个体和分裂后的个体进行了光学显微镜观察，并对来自施密丁格氏虫培养物的主要经冷冻固定的标本进行了透射电子显微镜观察。我们的研究重建了LFM的成熟过程，确定了两个主要发育阶段：桑葚状前体颗粒和成熟颗粒。后者聚集在前仔虫的腹侧部分，在大颗粒中嵌入有一条小颗粒的周边纵向带。在超微结构和化学性质上，两种大小类别的成熟颗粒是相同的。通过详细的实时观察，我们首次跟踪并记录了细胞分裂过程、前仔虫的行为、LFM颗粒的释放以及外壳形成的特征。
