Table S6 Abundance assessment of KEGG genes associated with cyanobacteria-heterotrophic bacteria interactions based on Tara Oceans macrogenomic data from Enhanced nutrient supply promotes mutualistic interactions between cyanobacteria and bacteria in oligotrophic ocean

Cyanobacteria can form complex interactions with heterotrophic microorganisms, but this relationship is susceptible to nutrient concentrations. Disentangling the cyanobacteria-bacteria interactions in relation to nutrient supply is essential to understanding their roles in geochemical cycles under global change. We hypothesize that enhanced nutrient supply in oligotrophic oceans can promote interactions among cyanobacteria and bacteria. Therefore, we investigated the planktonic bacteria and their interactions with cyanobacteria in relation to elevated nutrients caused by enhanced upwelling around a shallow and a deep seamount in the tropical western Pacific Ocean. We found obviously higher complexity of network occurred with significantly more cyanobacteria in the deep chlorophyll maximum (DCM) layer of shallow seamount when compared to that of deep seamount. Cyanobacteria can shape bacterial interaction and community evenness in response to relatively high nutrient concentrations. The effects of the nutrients on cyanobacteria-related networks were further estimated based on the <i>Tara</i> Oceans data. Statistical analyses further showed a facilitative effect of nitrate concentrations on cyanobacteria-bacteria mutualistic interactions in the global oligotrophic ocean. By analysing the <i>Tara</i> Ocean macrogenomic data, we detected functional genes related to cyanobacteria-bacteria interactions in all samples, indicating the existence of a mutualistic relationship. Our results reveal the cyanobacteria-bacteria interaction in response to nutrient elevation in oligotrophic ocean and highlight the potentially negative effects of global change on the bacterial community from the views of the bio-interaction.

蓝细菌（Cyanobacteria）可与异养微生物形成复杂的相互作用，但其关系易受营养盐浓度的影响。厘清与营养盐供给相关的蓝细菌-细菌相互作用，对于理解全球变化背景下二者在地球化学循环中的生态作用至关重要。我们提出假说：寡营养海洋中营养盐供给的提升可促进蓝细菌与细菌之间的相互作用。据此，我们针对热带西太平洋一浅海山与一深海山周边由增强型上升流引发的营养盐升高现象，开展了浮游细菌及其与蓝细菌相互作用的相关研究。研究发现，相较于深海山，浅海山的深层叶绿素最大值（DCM）层中蓝细菌丰度显著更高，且共生网络的复杂性也明显更强。蓝细菌可响应相对较高的营养盐浓度，调控细菌的相互作用与群落均匀度。基于塔拉海洋（Tara Oceans）项目的数据，我们进一步评估了营养盐对蓝细菌相关共生网络的影响。统计分析进一步表明，在全球寡营养海洋中，硝酸盐浓度对蓝细菌-细菌的互利相互作用具有显著促进效应。通过分析塔拉海洋（Tara Oceans）宏基因组数据，我们在所有样本中均检测到与蓝细菌-细菌相互作用相关的功能基因，证实了互利关系的广泛存在。本研究揭示了寡营养海洋中蓝细菌-细菌相互作用对营养盐升高的响应，并从生物相互作用的视角，凸显了全球变化可能对细菌群落产生的潜在负面影响。