ABSTRACT: The direct proximity of phytoplankton cells is a habitat distinct from the surrounding water. Colonizers of this habitat may form strong or weak associations with the host cells, depending on the mode of interaction and the prevailing abiotic conditions. We analyzed the bacteria and eukaryotes associated with the cyanobacterium Nodularia spumigena using Illumina Mi-Seq sequencing of bloom samples from the Baltic Sea, samples cultured for 2.5 mo and 2.5 yr after segregation, and a >3 yr old previously established lab culture. Significant differences in the composition of the associated communities between the different samples and a diversity that decreased significantly with increasing cultivation time demonstrated that most associations were labile and that culture conditions are a key driver of the associated community composition. However, present in all samples were 12 associated bacterial operational taxonomic units (OTUs) and 1 eukaryotic OTU, indicating the stable and possibly specific associations of the respective organisms with N. spumigena. Among the ubiquitous OTUs were 4 genera of Alphaproteobacteria (Roseibacterium, Hyphomonas, Brevundimonas, and Marivita), 1 genus of Betaproteobacteria (Limnobacter), and the fungus Malassezia, which were all highly abundant, suggesting key roles in associations of N. spumigena. Our findings suggest that the microbial community associated with N. spumigena contains a few stably associated taxa that play key roles in the associations, whereas the majority of accompanying organisms are more loosely associated, and their composition is apparently determined by the prevailing abiotic conditions.

中文翻译：

---

稳定的和不稳定的微生物与蓝藻结节菌协会。

摘要：浮游植物细胞的直接接近是一个不同于周围水域的栖息地。该生境的定居者可能与宿主细胞形成强弱关联，这取决于相互作用的方式和普遍的非生物条件。我们分析了与蓝藻结节菌相关的细菌和真核生物使用Illumina Mi-Seq测序法对波罗的海的水华样品进行了测序，分离后培养了2.5 mo和2.5 yr的样品，以及之前建立的大于3年的实验室培养物。不同样本之间相关社区组成的显着差异以及随着培养时间的增加而显着降低的多样性表明，大多数关联都不稳定，并且培养条件是相关社区组成的关键驱动力。但是，在所有样品中均存在12个相关的细菌操作分类单位（OTU）和1个真核OTU，这表明各个生物体与N. spumigena具有稳定且可能的特定关联。在普遍存在的OTU中，有4个属Alphaproteobacteria（Roseibacterium，Hyphomonas，短波单胞，和Marivita），1个属的β-变形菌（Limnobacter），和真菌马拉色氏霉菌等，这都非常丰富，这表明在协会关键作用N. spumigena。我们的研究结果表明，与Spumigena N.相关的微生物群落包含一些稳定相关的分类单元，这些分类单元在该关联中起关键作用，而大多数伴随生物则松散相关，它们的组成显然是由主要的非生物条件决定的。