Symbioses between plants and nitrogen-fixing cyanobacteria are benchmark biological systems to understand mutualism and patterns of coevolution. The diversity of cyanobacteria associated to non-vascular land plants is still being unraveled, with a huge gap in knowledge from tropical areas, especially in hornworts. We focus on the Neotropical hornwort Leiosporoceros dussii, which has a semi-permanent association with cyanobacteria. Unlike other hornworts, the peculiar Nostoc canals suggest cyanobiont specificity and selectivity. Here, we characterize the first hornwort bacteriome and focus on the endophytic cyanobacteria by describing its morphology, metagenomic diversity and phylogeny between two sampling sites in Panama. First, we use a metagenomic analyses (16S) from gametophytes from Río El Guayabo and Río Indio in Panama to identify the endophytic bacteria community of L. dussii. To provide more information on the cyanobacterial endophytes, we have extracted cyanobacterial endophytes to measure cell size variation and use the markers trnL and rbcLX to determine their phylogenetic relationships. Finally, we use stable isotope δ ¹⁵N to assess nitrogen flow in the plants. We find little diversity in Leiosporoceros bacteriome but observe significant community variations between sites. Results indicate a lack of cyanobacterial specificity of cyanobacteria associated to Leiosporoceros, with six unrelated clades of Nostoc forming a polyphyletic assemblage. Four clades are nested within bacteria collected as free-living taxa suggesting that typically non-symbiotic cyanobacteria can be associated with this hornwort. Finally, the little nitrogen fractioning of the plant suggests the role of the cyanobacterial symbionts in nitrogen fixation. This study provides the first hornwort bacteriome and is an important step in the characterization of tropical bryophyte symbioses.

中文翻译：

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在附近的两个地方，金鱼草Leiosporoceros dussii的相反细菌群着重于金鱼草-蓝细菌共生

植物与固氮蓝细菌之间的共生是基准生物学系统，可以理解共生和共进化模式。与非维管植物相关的蓝细菌的多样性仍在研究中，热带地区，尤其是金鱼草的知识差距很大。我们专注于新热带金鱼草Leiosporoceros dussii，它与蓝细菌具有半永久性关联。不同于其他金鱼草，奇特的Nostoc运河暗示氰基苯酚的特异性和选择性。在这里，我们通过描述其在巴拿马两个采样点之间的形态，宏基因组多样性和系统发育特征来表征第一个金银花细菌群，并着重于内生蓝藻细菌。首先，我们使用来自巴拿马RíoEl Guayabo和RíoIndio配子体的宏基因组分析（16S）来鉴定杜氏乳杆菌的内生细菌群落。为了提供有关蓝藻内生菌的更多信息，我们提取了蓝藻内生菌以测量细胞大小变化并使用标记物trnL和rbcLX来确定它们的系统发生关系。最后，我们使用稳定同位素δ ¹⁵ N到评估植物中的氮气流。我们在Leiosporoceros中发现很少的多样性细菌组，但观察到站点之间的显着群落差异。结果表明缺乏与Leiosporoceros相关的蓝细菌的蓝细菌特异性，与Nostoc的六个无关的进化枝形成了多系组合。四个进化枝被嵌套在以自由活动类群收集的细菌中，这表明典型的非共生性蓝细菌可以与这种金角麦有关。最后，植物中很少的氮分馏表明蓝细菌共生体在固氮中的作用。这项研究提供了首个金银花细菌群，并且是表征热带苔藓植物共生体的重要步骤。