This study investigated protist community composition and biotic interactions focusing on microplankton at four distinct sites around the Kerguelen Islands (Southern Ocean) after the summer phytoplankton bloom. Protist diversity in different size fractions, sampled with Niskin bottles and plankton nets, was assessed by sequencing of the V4 18S rDNA region. Combining different approaches, i.e. sequencing of different plankton size fractions, and isolation and sequencing of single cells, provided new insights into microbial interactions in protist communities. The communities displayed high variability, including short-term fluctuations in relative abundance of large protists (>35 μm) highlighted by the plankton net samples. Size fractionation of protist communities showed high concentrations of free Syndiniales spores but relatively few Syndiniales associated with microplankton, suggesting low parasitic infection in early autumn. Co-variance network analyses and sequencing of individually isolated single cells highlighted the important role of Rhizaria as consumers of a wide range of different diatom taxa. The data also raised the hypothesis that different Syndiniales clades might be directly or indirectly associated with some diatom genera, thus suggesting a potentially wider host range of these parasites than has been previously reported. These associations and the potential impact on carbon fluxes are discussed.

这项研究调查了夏季浮游植物开花后在Kerguelen群岛（南大洋）周围四个不同地点的浮游生物的原生生物群落组成和生物相互作用。通过对V4 18S rDNA区域进行测序，评估了使用Niskin瓶和浮游生物网采样的不同大小部分的原生生物多样性。结合不同的方法，即对不同的浮游生物大小级分进行测序，以及对单个细胞进行分离和测序，提供了对原生生物群落中微生物相互作用的新见解。群落表现出高度的可变性，包括浮游生物网样本突出的大型生物（> 35μm）的相对丰度的短期波动。原生生物群落的大小分级显示出高浓度的游离Syndiniales孢子，但与浮游生物相关的Syndiniales相对较少，表明在初秋的寄生虫感染率较低。协方差网络分析和单个分离的单个细胞的测序突出了根瘤菌作为各种不同硅藻类群的消费者的重要作用。数据还提出了这样的假说，即不同的Syndiniales进化枝可能与某些硅藻属直接或间接相关，因此表明这些寄生虫的宿主范围可能比以前报道的范围更大。讨论了这些关联以及对碳通量的潜在影响。协方差网络分析和单个分离的单个细胞的测序突显了根瘤菌作为各种不同硅藻类群的消费者的重要作用。数据还提出了这样的假说，即不同的Syndiniales进化枝可能与某些硅藻属直接或间接相关，因此表明这些寄生虫的宿主范围可能比以前报道的范围更大。讨论了这些关联以及对碳通量的潜在影响。协方差网络分析和单个分离的单个细胞的测序突出了根瘤菌作为各种不同硅藻类群的消费者的重要作用。数据还提出了这样的假说，即不同的Syndiniales进化枝可能与某些硅藻属直接或间接相关，因此表明这些寄生虫的宿主范围可能比以前报道的范围更大。讨论了这些关联以及对碳通量的潜在影响。