Data from: Evolving interactions between diazotrophic cyanobacterium and phage mediate nitrogen release and host competitive ability

Interactions between nitrogen-fixing (i.e. diazotrophic) cyanobacteria and their viruses, cyanophages, can have large-scale ecosystem effects. These effects are mediated by temporal alterations in nutrient availability in aquatic systems owing to the release of nitrogen and carbon sources from cells lysed by phages, as well as by ecologically important changes in the diversity and fitness of cyanobacterial populations that evolve in the presence of phages. However, ecological and evolutionary feedbacks between phages and nitrogen-fixing cyanobacteria are still relative poorly understood. Here, we used an experimental evolution approach to test the effect of interactions between a common filamentous, nitrogen-fixing cyanobacterium (Nodularia sp.) and its phage on cellular nitrogen release and host properties. Ecological, community-level effects of phage-mediated nitrogen release were tested with a phytoplankton bioassay. We found that cyanobacterial nitrogen release increased significantly as a result of viral lysis, which was associated with enhanced growth of phytoplankton species in cell-free filtrates compared with phage-resistant host controls in which lysis and subsequent nutrient release did not occur after phage exposure. We also observed an ecologically important change among phage-evolved cyanobacteria with phage-resistant phenotypes, a short-filamentous morphotype with reduced buoyancy compared with the ancestral long-filamentous morphotype. Reduced buoyancy might decrease the ability of these morphotypes to compete for light compared with longer, more buoyant filaments. Together, these findings demonstrate the potential of cyanobacteria–phage interactions to affect ecosystem biogeochemical cycles and planktonic community dynamics.固氮（即diazotrophic）蓝细菌与其病毒——蓝细菌噬菌体（cyanophages）之间的相互作用，可对生态系统产生大范围影响。此类效应的介导途径包括两方面：一是噬菌体裂解宿主细胞后释放氮源与碳源，引发水生系统中养分有效性的时序性改变；二是噬菌体存在条件下演化的蓝细菌种群的多样性与适合度发生具有生态学意义的变化。然而，目前学界对噬菌体与固氮蓝细菌之间的生态与演化反馈机制仍知之甚少。本研究采用实验演化方法，探究常见的丝状固氮蓝细菌（*Nodularia* sp.，结节藻属未定种）与其噬菌体之间的相互作用对细胞氮释放及宿主特性的影响。我们通过浮游植物生物测定实验，验证了噬菌体介导的氮释放所产生的生态及群落水平效应。研究发现，病毒裂解会显著提升蓝细菌的氮释放量；与噬菌体抗性宿主对照组（噬菌体侵染后未发生裂解及后续养分释放）相比，无细胞滤液中的浮游植物物种生长得到显著促进。此外，我们还在经噬菌体演化获得抗性表型的蓝细菌中观察到一项具有生态学意义的变化：相较于祖先型长丝状形态型，此类蓝细菌呈现出短丝状形态，且浮力降低。浮力降低可能会削弱此类形态相较于更长、浮力更强的丝状蓝细菌的光竞争能力。综上，本研究结果表明，蓝细菌与噬菌体的相互作用具备影响生态系统生物地球化学循环及浮游群落动态的潜力。