Biological interactions underpin the functioning of marine ecosystems, be it via competition, predation, mutualism or symbiosis processes. Microbial phototroph-heterotroph interactions propel the engine that results in the biogeochemical cycling of individual elements, and they are critical for understanding and modelling global ocean processes. Unfortunately, studies thus far have focused on exponentially growing cultures in nutrient-rich media, meaning knowledge of such interactions under in situ conditions is rudimentary at best. Here, we have performed long-term phototroph-heterotroph co-culture experiments under nutrient-amended and natural seawater conditions, and show that it is not the concentration of nutrients but rather their circulation that maintains a stable interaction and a dynamic system. Using the Synechococcus-Roseobacter interaction as a model phototroph-heterotroph case study, we show that although Synechococcus is highly specialized for carrying out photosynthesis and carbon fixation, it relies on the heterotroph to remineralize the inevitably leaked organic matter, making nutrients circulate in a mutualistic system. In this sense we challenge the general belief that marine phototrophs and heterotrophs compete for the same scarce nutrients and niche space, and instead suggest that these organisms more probably benefit from each other because of their different levels of specialization and complementarity within long-term stable-state systems.

中文翻译：

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养分循环促进海洋微生物光养异养相互作用的长期稳定性。

生物相互作用是海洋生态系统功能的基础，无论是通过竞争、捕食、共生还是共生过程。微生物光养异养相互作用推动了导致单个元素生物地球化学循环的引擎，它们对于理解和模拟全球海洋过程至关重要。不幸的是，迄今为止的研究都集中在营养丰富的培养基中呈指数增长的培养物，这意味着在原位条件下对这种相互作用的了解充其量只是初步的。在这里，我们在养分改良和天然海水条件下进行了长期的光养异养共培养实验，结果表明，维持稳定相互作用和动态系统的不是养分的浓度，而是它们的循环。使用聚球藻 - 玫瑰杆菌相互作用作为模型光养 - 异养案例研究，我们表明虽然聚球藻高度专门用于进行光合作用和碳固定，但它依赖异养来再矿化不可避免的泄漏有机物，使营养物质在互惠互利中循环系统。从这个意义上说，我们挑战了海洋光养生物和异养生物竞争相同稀缺养分和生态位空间的普遍信念，而是建议这些生物更有可能相互受益，因为它们在长期稳定的过程中具有不同的专业化水平和互补性——国家系统。它依靠异养生物将不可避免地泄漏的有机物再矿化，使营养物质在共生系统中循环。从这个意义上说，我们挑战了海洋光养生物和异养生物竞争相同稀缺养分和生态位空间的普遍信念，而是建议这些生物更有可能相互受益，因为它们在长期稳定的过程中具有不同的专业化水平和互补性——国家系统。它依靠异养生物将不可避免地泄漏的有机物再矿化，使营养物质在共生系统中循环。从这个意义上说，我们挑战了海洋光养生物和异养生物竞争相同稀缺养分和生态位空间的普遍信念，而是建议这些生物更有可能相互受益，因为它们在长期稳定的过程中具有不同的专业化水平和互补性——国家系统。