Marine Department, Centre Scientifique de Monaco, 8 Quai Antoine Ier, MC-98000, Monaco, Principality of Monaco.
Sorbonne Universités, UPMC Univ Paris 06, UMR 7093, LOV, Observatoire océanologique, F-06230, Villefranche/mer, France.
Environ Microbiol. 2019 Jan;21(1):480-495. doi: 10.1111/1462-2920.14480. Epub 2018 Dec 19.
Dinitrogen (N ) fixing bacteria (diazotrophs) are an important source of new nitrogen in oligotrophic environments and represent stable members of the microbiome in tropical corals, while information on corals from temperate oligotrophic regions is lacking. Therefore, this study provides new insights into the diversity and activity of diazotrophs associated with the temperate coral Oculina patagonica from the Mediterranean Sea by combining metabarcoding sequencing of amplicons of both the 16S rRNA and nifH genes and N stable isotope tracer analysis to assess diazotroph-derived nitrogen (DDN) assimilation by the coral. Results show that the diazotrophic community of O. patagonica is dominated by autotrophic bacteria (i.e. Cyanobacteria and Chlorobia). The majority of DDN was assimilated into the tissue and skeletal matrix, and DDN assimilation significantly increased in bleached corals. Thus, diazotrophs may constitute an additional nitrogen source for the coral host, when nutrient exchange with Symbiodinium is disrupted (e.g. bleaching) and external food supply is limited (e.g. oligotrophic summer season). Furthermore, we hypothesize that DDN can facilitate the fast proliferation of endolithic algae, which provide an alternative carbon source for bleached O. patagonica. Overall, O. patagonica could serve as a good model for investigating the importance of diazotrophs in coral recovery from bleaching.
固氮细菌（固氮生物）是贫营养环境中新生氮的重要来源，也是热带珊瑚微生物组中的稳定成员，而有关来自温带贫营养地区的珊瑚的信息则较为缺乏。因此，本研究通过结合 16S rRNA 和 nifH 基因扩增子的宏条形码测序和 N 稳定同位素示踪分析，为来自地中海的温带珊瑚 Oculina patagonica 相关固氮生物的多样性和活性提供了新的见解，以评估珊瑚对固氮生物衍生氮（DDN）的同化作用。结果表明，O. patagonica 的固氮生物群落主要由自养细菌（即蓝细菌和绿菌）组成。大部分 DDN 被同化到组织和骨骼基质中，并且在白化珊瑚中 DDN 的同化作用显著增加。因此，当与共生藻的营养交换受到干扰（如白化）且外部食物供应有限（如贫营养的夏季）时，固氮生物可能成为珊瑚宿主的另一个氮源。此外，我们假设 DDN 可以促进内生藻类的快速增殖，为白化的 O. patagonica 提供替代的碳源。总的来说，O. patagonica 可以作为研究固氮生物在珊瑚白化恢复中的重要性的良好模型。
