Phytoplankton and their associated microbiomes of heterotrophic bacteria are foundational to primary production, energy transfer, and biogeochemical cycling in aquatic systems. While it is known that these microbiomes are shaped by host-released dissolved organic matter (DOM), the extent to which dynamic phytoplankton-bacteria interactions shape bacterial community assembly remains to be examined. Here, we investigated the effects of two mechanisms in host-microbiome interactions on phytoplankton bacterial microbiome formation: (i) innate host selection and (ii) host-microbiome feedback. For the former, phytoplankton-produced DOM composition is based solely on the host's properties (species or physiological state); for the latter, the presence of the microbiome modifies host DOM production. The microbiome of Chlorella sorokiniana was extracted and exposed to six ratios of the two effects. We found that microbiome composition changed along with the six host-microbiome feedback versus innate host selection ratios, with the highest compositional distance between communities under the strongest and the weakest ratio of the two effects. This indicates that each mechanism selects for different bacterial species. In addition, our findings showed that when both selective forces were applied, it led to a higher community richness, while host-microbiome feedback alone reduces community evenness due to its strong species-specific selection.

中文翻译：

---

剖析宿主-微生物组相互作用对浮游植物微生物组组成和多样性的影响

浮游植物及其相关的异养细菌微生物组是水生系统初级生产、能量转移和生物地球化学循环的基础。虽然已知这些微生物群是由宿主释放的溶解有机物 (DOM) 形成的，但浮游植物-细菌的动态相互作用在多大程度上影响细菌群落的组装仍有待研究。在这里，我们研究了宿主-微生物组相互作用的两种机制对浮游植物细菌微生物组形成的影响：（i）先天宿主选择和（ii）宿主-微生物组反馈。对于前者，浮游植物产生的 DOM 组成完全取决于宿主的特性（物种或生理状态）；对于后者，微生物组的存在会改变宿主 DOM 的产生。提取小球藻的微生物组并暴露于两种效应的六种比例。我们发现，微生物组的组成随着六种宿主-微生物组反馈与先天宿主选择比率的变化而变化，在两种效应最强和最弱的比率下，群落之间的组成距离最大。这表明每种机制选择不同的细菌种类。此外，我们的研究结果表明，当应用两种选择力时，会导致更高的群落丰富度，而宿主微生物组反馈本身会由于其强烈的物种特异性选择而降低群落均匀度。