Water Quality Engineering, Technical University of Berlin, Berlin, Germany.
Leibniz-Institute for Baltic Sea Research, Warnemuende, Germany.
Appl Environ Microbiol. 2023 Jul 26;89(7):e0053923. doi: 10.1128/aem.00539-23. Epub 2023 Jul 6.
Phytoplankton-bacterium interactions are mediated, in part, by phytoplankton-released dissolved organic matter (DOMp). Two factors that shape the bacterial community accompanying phytoplankton are (i) the phytoplankton producer species, defining the initial composition of released DOMp, and (ii) the DOMp transformation over time. We added phytoplankton DOMp from the diatom Skeletonema marinoi and the cyanobacterium Prochlorococcus marinus MIT9312 to natural bacterial communities from the eastern Mediterranean and determined the bacterial responses over a time course of 72 h in terms of cell numbers, bacterial production, alkaline phosphatase activity, and changes in active bacterial community composition based on rRNA amplicon sequencing. Both DOMp types were demonstrated to serve the bacterial community as carbon and, potentially, phosphorus sources. Bacterial communities in diatom-derived DOM treatments maintained higher Shannon diversities throughout the experiment and yielded higher bacterial production and lower alkaline phosphatase activity compared to cyanobacterium-derived DOM after 24 h of incubation (but not after 48 and 72 h), indicating greater bacterial usability of diatom-derived DOM. Bacterial communities significantly differed between DOMp types as well as between different incubation times, pointing to a certain bacterial specificity for the DOMp producer as well as a successive utilization of phytoplankton DOM by different bacterial taxa over time. The highest differences in bacterial community composition with DOMp types occurred shortly after DOMp additions, suggesting a high specificity toward highly bioavailable DOMp compounds. We conclude that phytoplankton-associated bacterial communities are strongly shaped by the phytoplankton producer as well as the transformation of its released DOMp over time. Phytoplankton-bacterium interactions influence biogeochemical cycles of global importance. Phytoplankton photosynthetically fix carbon dioxide and subsequently release the synthesized compounds as dissolved organic matter (DOMp), which becomes processed and recycled by heterotrophic bacteria. Yet the importance of phytoplankton producers in combination with the time-dependent transformation of DOMp compounds on the accompanying bacterial community has not been explored in detail. The diatom and the cyanobacterium Prochlorococcus marinus MIT9312 belong to globally important phytoplankton genera, and our study revealed that DOMp of both species was selectively incorporated by the bacterial community. The producer species had the highest impact shortly after DOMp appropriation, and its effect diminished over time. Our results improve the understanding of the dynamics of organic matter produced by phytoplankton in the oceans as it is utilized and modified by cooccurring bacteria.
浮游植物-细菌相互作用部分受浮游植物释放的溶解有机物质（DOMp）介导。影响伴随浮游植物的细菌群落的两个因素是：（i）浮游植物生产者物种，决定了释放的 DOMp 的初始组成，以及（ii）DOMp 随时间的转化。我们将来自硅藻 Skeletonema marinoi 和蓝藻 Prochlorococcus marinus MIT9312 的浮游植物 DOMp 添加到来自东地中海的自然细菌群落中，并在 72 小时的时间过程中确定了细菌的反应，具体指标包括细胞数量、细菌生产力、碱性磷酸酶活性以及基于 rRNA 扩增子测序的活性细菌群落组成的变化。这两种 DOMp 类型均被证明是细菌群落的碳源，并且可能是磷源。在整个实验过程中，来源于硅藻的 DOM 处理的细菌群落保持较高的香农多样性，并且在孵育 24 小时后，与来源于蓝藻的 DOM 相比，细菌生产力更高，碱性磷酸酶活性更低（但在 48 小时和 72 小时后则不然），这表明硅藻来源的 DOM 更易被细菌利用。DOMp 类型之间以及不同孵育时间之间的细菌群落差异显著，这表明 DOMp 生产者具有一定的细菌特异性，并且随着时间的推移，不同的细菌类群会相继利用浮游植物 DOMp。与 DOMp 类型相比，细菌群落组成的差异在添加 DOMp 后不久就达到最大，这表明对高生物利用性 DOMp 化合物具有高度特异性。我们得出结论，浮游植物相关的细菌群落受浮游植物生产者以及其释放的 DOMp 随时间的转化的强烈影响。浮游植物光合作用固定二氧化碳，随后将合成的化合物释放为溶解有机物质（DOMp），异养细菌对其进行处理和再循环。然而，浮游植物生产者的重要性以及 DOMp 化合物随时间的转化对伴随的细菌群落的影响尚未得到深入探讨。硅藻和蓝藻 Prochlorococcus marinus MIT9312 属于全球重要的浮游植物属，我们的研究表明，这两个物种的 DOMp 都被细菌群落选择性地吸收。生产者物种在 DOMp 被吸收后不久就产生了最大的影响，随着时间的推移其影响逐渐减弱。我们的研究结果提高了对海洋中浮游植物产生的有机物动态的认识，因为它被共存的细菌利用和修饰。
