Coët Arthur, Bastos Cécile Carpaneto, Lechelon Mathias, Hawley Ruth, Flanagan Oliver, Lohan Maeve C, Ronceray Pierre, Hopkins Joanne E, Mahaffey Claire, Benavides Mar
Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France.
Aix Marseille Univ, CNRS, CINAM, Turing Centre for Living Systems, Marseille, France.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wraf098.
Global warming is causing sea ice retreat and intensifying algal blooms in the Arctic Ocean, in turn increasing nitrogen limitation in surface waters. Dinitrogen fixation by diazotrophic microorganisms, usually favored in low reactive nitrogen systems, may become an increasingly important source of nitrogen in the Arctic. Previous studies have shown that non-cyanobacterial diazotrophs are dominant in the Arctic Ocean. Lacking a photosynthetic apparatus, non-cyanobacterial diazotrophs may utilize organic particles as carbon- and energy-rich niches. However, cyanobacterial diazotrophs may also form particles by aggregation. To further understand diazotroph-particle associations, here we study the chemotactic behavior and colonization dynamics of diazotrophs on model organic particles using a modified chemotaxis assay. Artificial organic particles (agarose, alginate) were incubated with surface seawater communities from four contrasted stations in the Barents Sea, and their DNA was sequenced targeting nifH and 16S rRNA genes after 2, 36, and 72 h of incubation. Our results show that diazotroph groups have selective colonization behaviors, with Gammaproteobacteria members preferentially colonizing alginate particles derived from brown algae, a form of organic matter becoming more common in the Arctic as it warms up. We also observe niche partitioning among microbial groups, with diazotrophs colonizing nitrogen-poor, carbon-rich particles earlier than non-diazotrophic prokaryotes. As Arctic warming proceeds, increased algal blooms may expand the niches for particle-associated diazotrophs, whose dinitrogen fixation supports phytoplankton growth and primary productivity.
全球变暖正在导致北冰洋海冰退缩，并加剧藻华，进而增加表层水体中的氮限制。固氮微生物进行的双氮固定，通常在低活性氮系统中占优势，可能会成为北极地区越来越重要的氮源。此前的研究表明，非蓝藻固氮菌在北冰洋占主导地位。非蓝藻固氮菌缺乏光合装置，可能会利用有机颗粒作为富含碳和能量的生态位。然而，蓝藻固氮菌也可能通过聚集形成颗粒。为了进一步了解固氮菌与颗粒的关联，我们在此使用改良的趋化性分析方法，研究了固氮菌在模型有机颗粒上的趋化行为和定殖动态。将人工有机颗粒（琼脂糖、藻酸盐）与巴伦支海四个不同站点的表层海水群落一起培养，并在培养2、36和72小时后，针对nifH和16S rRNA基因对其DNA进行测序。我们的结果表明，固氮菌群具有选择性定殖行为，γ-变形菌纲成员优先定殖于源自褐藻的藻酸盐颗粒，随着北极变暖，这种有机物质形式在北极变得越来越普遍。我们还观察到微生物群体之间的生态位划分，固氮菌比非固氮原核生物更早定殖于贫氮、富碳的颗粒。随着北极变暖的持续，藻华增加可能会扩大与颗粒相关的固氮菌的生态位，其双氮固定支持浮游植物生长和初级生产力。
