An intricate set of interactions characterizes marine ecosystems. One of the most important is represented by the microbial loop, which includes the exchange of dissolved organic matter (DOM) from phototrophic organisms to heterotrophic bacteria. Here, it can be used as the major carbon and energy source. This interaction is one of the foundations of the entire ocean food-web. The carbon fixed by phytoplankton can be redirected to bacteria in two main ways; either (i) bacteria feed on dead phytoplankton cells or (ii) DOM is actively released by phytoplankton (a process resulting in up to 50% of the fixed carbon leaving the cell). Here, we have set up a co-culture of the diatom Phaeodactylum tricornutum and the chemoheterotrophic bacterium Pseudoalteromonas haloplanktis TAC125 and used this system to study the interactions between these two representatives of the microbial loop. We show that the bacterium can thrive on diatom-derived carbon and that this growth can be sustained by both diatom dead cells and diatom-released compounds. These observations were formalized in a network of putative interactions between P. tricornutum and P. haloplanktis and implemented in a model that reproduces the observed co-culture dynamics, revealing an overall accuracy of our hypotheses in explaining the experimental data.

中文翻译：

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缩小微生物循环：硅藻-细菌共培养中生长相互作用的数据驱动模型

一组错综复杂的相互作用是海洋生态系统的特征。其中最重要的一项是微生物循环，其中包括溶解有机物 (DOM) 从光养生物到异养细菌的交换。在这里，它可以作为主要的碳源和能源。这种相互作用是整个海洋食物网的基础之一。浮游植物固定的碳可以通过两种主要方式重定向到细菌；(i) 细菌以死亡的浮游植物细胞为食，或 (ii) DOM 由浮游植物主动释放（这一过程导致高达 50% 的固定碳离开细胞）。在这里，我们建立了硅藻三角褐指藻和化学异养细菌Pseudoalteromonas haloplanktis的共培养TAC125 并使用该系统研究了这两个代表微生物循环之间的相互作用。我们表明，这种细菌可以在硅藻衍生的碳上茁壮成长，并且这种生长可以通过硅藻死细胞和硅藻释放的化合物来维持。这些观察结果在P. tricornutum和P. haloplanktis之间假定的相互作用网络中正式化，并在重现观察到的共培养动态的模型中实施，揭示了我们在解释实验数据时假设的整体准确性。