Department of Ecology and Genetics/Limnology, Uppsala University, Uppsala, Sweden.
Biological Oceanography, Institute for Baltic Sea Research in Warnemünde, Seestraße 15, Rostock, 18119, Germany.
Microb Ecol. 2024 Jan 18;87(1):33. doi: 10.1007/s00248-024-02344-9.
The freshwater raphidophyte Gonyostomum semen forms extensive summer blooms in northern European humic lakes. The development of these blooms might be facilitated by a lack of natural top-down control, as few zooplankton species are able to prey on these large algal cells (up to 100 μm) that expel trichocysts upon physical stress. In this study, we describe a small ciliate species (< 17 μm) that preys on G. semen by damaging the cell membrane until cytoplasm and organelles spill out. Sequencing of clonal cultures of the ciliate tentatively identified it as the prostomatid species Urotricha pseudofurcata. Grazing experiments illustrated that feeding by U. cf. pseudofurcata can significantly reduce cell concentrations of the microalga. However, differences in cell size and growth rate between two investigated ciliate strains resulted in noticeably different grazing pressure. Environmental sequencing data from five different lakes supported potential interactions between the two species. Urotricha cf. pseudofurcata might, thus, play an important role in aquatic ecosystems that are regularly dominated by G. semen, reducing the abundance of this bloom-forming microalga and enabling transfer of organic carbon to higher trophic levels.
淡水旋口藻在北欧富营养化湖泊中形成了广泛的夏季水华。这些水华的发展可能得益于缺乏自然的自上而下的控制，因为很少有浮游动物物种能够捕食这些能够在受到物理压力时释放出刺丝囊的大型藻类细胞（最大可达 100 μm）。在这项研究中，我们描述了一种小型纤毛虫物种（<17 μm），它通过破坏细胞膜来捕食 G. semen，直到细胞质和细胞器溢出。对纤毛虫的克隆培养物进行测序，初步确定它是前毛口目物种 Urotricha pseudofurcata。摄食实验表明，U. cf. pseudofurcata 的摄食可以显著降低微藻的细胞浓度。然而，两种研究的纤毛虫菌株之间的细胞大小和生长率的差异导致了明显不同的摄食压力。来自五个不同湖泊的环境测序数据支持这两个物种之间存在潜在的相互作用。Urotricha cf. pseudofurcata 可能因此在经常被 G. semen 主导的水生生态系统中发挥重要作用，减少这种形成水华的微藻的丰度，并使有机碳转移到更高的营养水平。
