Fernández-Juárez Víctor, Bennasar-Figueras Antoni, Sureda-Gomila Antoni, Ramis-Munar Guillem, Agawin Nona S R
Marine Ecology and Systematics (MarES), Department of Biology, University of the Balearic Islands, Palma, Spain.
Grup de Microbiologia, Department of Biology, University of the Balearic Islands, Palma, Spain.
Front Microbiol. 2020 Sep 25;11:541558. doi: 10.3389/fmicb.2020.541558. eCollection 2020.
Diazotrophs or N-fixers are one of the most ecologically significant groups in marine ecosystems (pelagic and benthic). Inorganic phosphorus (PO ) and iron (Fe) can limit the growth and N-fixing capacities of cyanobacteria. However, studies investigating co-limitation of these factors are lacking. Here, we added different concentrations of PO and Fe in two cyanobacterial species whose relatives can be found in seagrass habitats: the unicellular sp. (PCC 7418) and the filamentous (PCC 73103), grown under different nitrate (NO ) concentrations and under N as sole N source, respectively. Their growth, pigment content, N-fixation rates, oxidative stress responses, and morphological and cellular changes were investigated. Our results show a serial limitation of NO and PO (with NO as the primary limiting nutrient) for sp. Simultaneous co-limitation of PO and Fe was found for both species tested, and high levels of Fe (especially when added with high PO levels) inhibited the growth of sp. Nutrient limitation (PO , Fe, and/or NO ) enhanced oxidative stress responses, morphological changes, and apoptosis. Furthermore, an extensive bio-informatic analysis describing the predicted Pho, Fur, and NtcA regulons (involved in the survival of cells to P, Fe, and N limitation) was made using the complete genome of sp. as a model, showing the potential of this strain to adapt to different nutrient regimes (P, Fe, or N).
固氮菌或氮固定菌是海洋生态系统（远洋和底栖）中最具生态意义的群体之一。无机磷（PO）和铁（Fe）会限制蓝细菌的生长和固氮能力。然而，缺乏对这些因素共同限制作用的研究。在此，我们在两种蓝细菌物种中添加了不同浓度的PO和Fe，其亲缘物种可在海草栖息地中找到：单细胞的sp.（PCC 7418）和丝状的（PCC 73103），分别在不同硝酸盐（NO）浓度下以及以N作为唯一氮源的条件下培养。我们研究了它们的生长、色素含量、固氮率、氧化应激反应以及形态和细胞变化。我们的结果表明，对于sp.而言，NO和PO存在序列限制（以NO作为主要限制营养素）。在所测试的两种物种中均发现PO和Fe同时存在共同限制，并且高水平的Fe（尤其是与高PO水平一起添加时）会抑制sp.的生长。营养限制（PO、Fe和/或NO）会增强氧化应激反应、形态变化和细胞凋亡。此外，以sp.的完整基因组为模型，进行了广泛的生物信息学分析，描述了预测的Pho、Fur和NtcA调控子（参与细胞对P、Fe和N限制的存活），显示了该菌株适应不同营养状况（P、Fe或N）的潜力。
