Whole microbial communities regularly merge with one another, often in tandem with their environments, in a process called community coalescence. Such events impose substantial changes: abiotic perturbation from environmental blending and biotic perturbation of community merging. We used an aquatic mixing experiment to independently unravel the effects of these perturbations on the whole microbiome response and on the success of individual taxa when distinct freshwater and marine communities coalesce. We found that an equal mix of freshwater and marine habitats and blended microbiomes resulted in strong convergence the community structure towards that of the marine microbiome. The enzymatic potential of these blended microbiomes in mixed media also converged toward that of the marine, with strong correlations between the multivariate response patterns of the enzymes and of community structure. Exposing each endmember inocula to an axenic equal mix of their freshwater and marine source waters led to a 96% loss of taxa from our freshwater microbiomes and a 66% loss from our marine microbiomes. When both inocula were added together to this mixed environment, interactions amongst the communities led to a further loss of 29% and 49% of freshwater and marine taxa, respectively. Under both the axenic and competitive scenarios, the diversity lost was somewhat counterbalanced by increased abundance of microbial taxa that were too rare to detect in the initial inocula. Our study emphasizes the importance of the rare biosphere as a critical component of microbial community responses to community coalescence.

中文翻译：

---

群落碰撞时出现稀有微生物分类群：淡水和海洋微生物组对实验混合的反应

整个微生物群落有规律地相互融合，通常与它们的环境一起，在一个称为群落合并的过程中。这些事件带来了实质性的变化：来自环境混合的非生物扰动和群落合并的生物扰动。我们使用水生混合实验独立揭示了这些扰动对整个微生物组反应以及不同淡水和海洋群落融合时个体分类群成功的影响。我们发现，淡水和海洋栖息地以及混合微生物群的平等混合导致群落结构向海洋微生物群落结构强烈融合。这些混合介质中的混合微生物组的酶促潜力也趋向于海洋、酶的多元反应模式与群落结构之间存在很强的相关性。将每个端元接种物暴露于淡水和海洋源水的无菌等量混合液中，导致淡水微生物群落的分类群减少了 96%，海洋微生物群落的分类群减少了 66%。当两种接种物一起添加到这种混合环境中时，群落之间的相互作用导致淡水和海洋类群分别进一步损失 29% 和 49%。在无菌和竞争情况下，多样性的丧失在某种程度上被微生物类群的丰度增加所抵消，这些微生物类群在最初的接种物中太罕见而无法检测到。我们的研究强调了稀有生物圈作为微生物群落对群落融合反应的关键组成部分的重要性。