Sorbonne Université, CNRS, UMR7144, Station Biologique de Roscoff, Roscoff, France.
Departamento de Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil.
ISME J. 2018 May;12(5):1360-1374. doi: 10.1038/s41396-018-0050-z. Epub 2018 Feb 9.
Symbioses between eukaryotic algae and nitrogen-fixing cyanobacteria have been recognized in recent years as a key source of new nitrogen in the oceans. We investigated the composition of the small photosynthetic eukaryote communities associated with nitrogen-fixing cyanobacteria in the Brazilian South Atlantic Bight using a combination of flow cytometry sorting and high throughput sequencing of two genes: the V4 region of 18S rRNA and nifH. Two distinct eukaryotic communities were often encountered, one dominated by the Mamiellophyceae Bathycoccus and Ostreococcus, and one dominated by a prymnesiophyte known to live in symbiosis with the UCYN-A1 nitrogen-fixing cyanobacterium. Among nifH sequences, those from UCYN-A1 were most abundant but three other UCYN-A clades (A2, A3, A4) were also found. Network analysis confirmed the relation between A1 and A2 clades and their hypothesized hosts and pointed out to the potential association between novel clade A4 with Braarudosphaera bigelowii, previously hypothesized to host A2.
近年来，人们已经认识到真核藻类和固氮蓝藻之间的共生关系是海洋中氮素的一个重要来源。我们使用流式细胞术分选和高通量测序两种方法（18S rRNA V4 区和 nifH 基因），研究了与巴西南大西洋湾固氮蓝藻共生的小型光合真核生物群落的组成。我们经常遇到两种不同的真核生物群落，一种以 Mamiellophyceae 的 Bathycoccus 和 Ostreococcus 为主，另一种以与 UCYN-A1 固氮蓝藻共生的甲藻为主。在 nifH 序列中，来自 UCYN-A1 的序列最为丰富，但也发现了其他三个 UCYN-A 分支（A2、A3、A4）。网络分析证实了 A1 和 A2 分支及其假定宿主之间的关系，并指出了新的 A4 分支与 Braarudosphaera bigelowii 之间可能存在的联系，此前曾假设 A2 与 Braarudosphaera bigelowii 共生。
