Department of Environmental Science, Stockholm Universitygrid.10548.38, Stockholm, Sweden.
Division of Marine Biotechnology, Institute of Oceanography, University of Gdańsk, Gdańsk, Poland.
Appl Environ Microbiol. 2022 Aug 9;88(15):e0096622. doi: 10.1128/aem.00966-22. Epub 2022 Jul 12.
Nodularia spumigena is a bloom-forming cyanobacterium that produces several classes of nonribosomal peptides (NRPs) that are biologically active; however, the ecological roles of specific NRPs remain largely unknown. Here, we explored the involvement of NRPs produced by N. spumigena in interspecific interactions by coculturing the cyanobacterium and its algal competitors, the diatom Phaeodactylum tricornutum and the cryptomonad Rhodomonas salina, and measuring NRP levels and growth responses in all three species. Contrary to the expected growth suppression in the algae, it was N. spumigena that was adversely affected by the diatom, while the cryptomonad had no effect. Reciprocal effects of N. spumigena on the algae were manifested as the prolonged lag phase in R. salina and growth stimulation in P. tricornutum; however, these responses were largely attributed to elevated pH and not to specific NRPs. Nevertheless, the NRP levels in the cocultures were significantly higher than in the monocultures, with an up to 5-fold upregulation of cell-bound nodularins and exudation of nodularin and anabaenopeptin. Thus, chemically mediated interspecific interactions can promote NRP production and release by cyanobacteria, resulting in increased input of these compounds into the water. NRPs were involved in growth responses of both cyanobacteria and algae; however, the primary driver of the growth trajectories was high pH induced by N. spumigena. Thus, the pH-mediated inhibition of eukaryotic phytoplankton may be involved in the bloom formation of N. spumigena. We also report, for the first time, the reciprocal growth inhibition of N. spumigena by diatoms resistant to alkaline conditions. As all species in this study can co-occur in the Baltic Sea during summer, these findings are highly relevant for understanding ecological interactions in planktonic communities in this and other systems experiencing regular cyanobacteria blooms.
节旋藻是一种形成水华的蓝藻，能产生多种生物活性的非核糖体肽（NRPs）；然而，特定 NRPs 的生态作用在很大程度上仍然未知。在这里，我们通过共培养蓝藻及其藻类竞争者——角毛藻和隐甲藻，并测量这三种生物的 NRPs 水平和生长反应，探索了节旋藻产生的 NRPs 在种间相互作用中的作用。与藻类预期的生长抑制相反，受影响的是节旋藻，而隐甲藻则没有影响。节旋藻对藻类的相互作用表现为隐甲藻的延长迟滞期和角毛藻的生长刺激；然而，这些反应主要归因于 pH 值的升高，而不是特定的 NRPs。尽管如此，共培养物中的 NRPs 水平明显高于单培养物，细胞结合的节旋肽、节旋肽和鱼腥藻肽的分泌分别上调了 5 倍。因此，化学介导的种间相互作用可以促进蓝藻 NRPs 的产生和释放，导致这些化合物更多地输入到水中。NRPs 参与了蓝藻和藻类的生长反应；然而，蓝藻生长轨迹的主要驱动因素是节旋藻诱导的高 pH 值。因此，pH 介导的真核浮游植物抑制可能参与了节旋藻的水华形成。我们还首次报道了对碱性条件有抗性的硅藻对节旋藻的相互生长抑制。由于本研究中的所有物种在夏季都可以在波罗的海共存，因此这些发现对于理解该系统和其他经常发生蓝藻水华的系统中浮游群落的生态相互作用具有重要意义。
