Phytoplankton-bacteria interactions represent the evolution of complex cross-kingdom networks requiring niche specialization of diverse microbes. Unraveling this co-evolutionary process has proven challenging because microbial partnerships are complex, and their assembly can be dynamic as well as scale- and taxon-dependent. Here, we monitored long-term experimental evolution of phytoplankton-bacteria interactions by reintroducing the intact microbiome into an axenized dinoflagellate Alexandrium tamarense to better understand microbiome assembly dynamics and how microbiome composition could shift and stabilize over 15 months. We examined host functioning by growth rate, photosynthetic capability, cell size, and other physiological signatures and compared it to associated microbial communities determined by 16S rRNA gene sequences. Our results showed that microbiome reconstitution did not restore the intact microbiome, instead a distinct microbial community shift to Roseobacter clade was observed in the re-established cultures. In-depth comparisons of microbial interactions revealed no apparent coupling between host physiology and specific bacterial taxa, indicating that highly represented, abundant taxa might not be essential for host functioning. The emergence of highly divergent Roseobacter clade sequences suggests fine-scale microbial dynamics driven by microdiversity could be potentially linked to host functioning. Collectively, our results indicate that functionally comparable microbiomes can be assembled from markedly different, highly diverse bacterial taxa in changing environments.

中文翻译：

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高分辨率系统发育分析揭示了浮游植物微生物组的长期微生物动态和微生物多样性

浮游植物-细菌相互作用代表了复杂的跨界网络的进化，需要不同微生物的生态位专门化。解开这个共同进化过程已被证明具有挑战性，因为微生物伙伴关系很复杂，它们的组装可以是动态的，也可以依赖于规模和分类单元。在这里，我们通过将完整的微生物组重新引入轴化甲藻Alexandrium tamarense来监测浮游植物-细菌相互作用的长期实验进化更好地了解微生物组组装动力学以及微生物组组成如何在 15 个月内发生变化和稳定。我们通过生长速率、光合能力、细胞大小和其他生理特征检查宿主功能，并将其与由 16S rRNA 基因序列确定的相关微生物群落进行比较。我们的结果表明，微生物组重建并没有恢复完整的微生物组，而是在重建的培养物中观察到明显的微生物群落向玫瑰杆菌进化枝的转变。对微生物相互作用的深入比较表明宿主生理学和特定细菌类群之间没有明显的耦合，表明高度代表性、丰富的类群可能对宿主功能不是必需的。高度分化的玫瑰杆菌的出现进化枝序列表明，由微多样性驱动的精细微生物动力学可能与宿主功能有关。总的来说，我们的结果表明，在不断变化的环境中，可以从明显不同、高度多样化的细菌类群中组装出功能相当的微生物组。