Viral lysis and protistan grazing are thought to be the major processes leading to microbial mortality in aquatic environments and thus regulate community diversity and biogeochemical cycling characteristics. Here, we studied nutrient cycling and bacterial responses to cyanophage‐mediated photoautotroph lysis and ciliate predation in a model Synechococcus–heterotroph co‐culture system. Both viral lysis and Euplotes grazing facilitated the transformation of organic carbon from biomass to dissolved organic matter with convention efficiencies of 20%–26%. The accumulation of ammonium after the addition of phages and ciliates suggested the importance of recycled NH₄⁺ occurred in the interactions between Synechococcus growth and heterotrophic bacterial metabolism of photosynthate. The slower efficiency of P mineralization compared to N (primarily ammonium) indicated that P‐containing organic matter was primarily integrated into bacterial biomass rather than being remineralized into inorganic phosphate under C‐rich conditions. In the cyanophage addition treatment, both Fluviicola and Alteromonas exhibited rapid positive responses to Synechococcus lysing, while Marivita exhibited an apparent negative response. Further, the addition of Euplotes altered the incubation system from a Synechococcus‐driven phycosphere to a ciliate‐remodelled zoosphere that primarily constituted grazing‐resistant bacteria and Euplotes symbionts. Top‐down controls increased co‐culture system diversity and resulted in a preference for free‐living lifestyles of dominant populations, which was accompanied by the transfer of matter and energy. Our results indicate top‐down control was particularly important for organic matter redistribution and inorganic nutrient regeneration between photoautotrophs and heterotrophs, and altered bacterial lifestyles. This study consequently sheds light on marine biogeochemical cycling and the interaction networks within these dynamic ecosystems.

中文翻译：

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模型河口自养-异养共培养系统中养分循环和种群动态的自上而下控制

病毒的溶解和Protistan放牧被认为是导致水生环境中微生物死亡的主要过程，从而调节了群落多样性和生物地球化学循环特征。在这里，我们研究了在模型Synechococcus -heterotroph共培养系统中养分循环以及细菌对蓝藻介导的光自养菌裂解和纤毛虫捕食的反应。病毒裂解和Euplotes放牧都促进了有机碳从生物质到溶解有机物的转化，常规效率为20％–26％。添加噬菌体和纤毛虫后铵盐的积累表明，回收的NH ₄ ⁺的重要性发生在Synechococcus之间的相互作用中光合产物的生长和异养细菌代谢。与N（主要是铵）相比，P的矿化效率较慢，表明含P的有机物主要整合到细菌生物质中，而不是在富含C的条件下再矿化成无机磷酸盐。在添加蓝藻的处理中，Fluviicola和Alteromonas对Synechococcus裂解均表现出快速的阳性反应，而Marivita表现出明显的阴性反应。此外，加游仆改变培养系统从聚球藻驱动的藻圈到纤毛虫重塑的动物圈，主要组成了抗放牧细菌和Euplotes共生体。自上而下的控制增加了共培养系统的多样性，并导致偏爱优势人口的自由生活方式，同时伴随着物质和能量的转移。我们的结果表明自上而下的控制对于光合自养生物和异养生物之间有机物的重新分配和无机养分的再生以及改变细菌的生活方式特别重要。因此，这项研究揭示了海洋生物地球化学循环以及这些动态生态系统中的相互作用网络。