一个群落中新物种的形成可能取决于它们到达该群落的顺序和时间，这种现象称为优先效应。来自加利福尼亚大学伯克利分校的主要研究人员在《Nature Reviews Microbiology》综述了优先效应的机制及其在哺乳动物肠道、植物叶际和根际等环境中微生物群落中的重要性。

Arrival historyinfluences succession when species that arrive earlieralter resources or environmental conditions in ways thatimpact species that arrive later, affecting their ability toestablish in the community. These interactions, knownas priority effects, can generate alternative successionaltrajectories for whole ecosystems.Researchers from University ofCalifornia, Berkeley reviewed the mechanisms of priority effects and evidence for their importancein microbial communities inhabiting a range of environments, including the mammalian gut,the plant phyllosphere and rhizosphere.

微生物的优先效应机制主要分为三种，包括“抢占生态位”、“促进生态位”和“抑制生态位”。当一个早到物种耗尽系统资源，从而抑制了晚到物种在该群落的建立，这种情况称为“抢占生态位”。“抢占生态位”，特别是营养竞争，是微生物组形成的一个重要过程。当一个早到物种改变环境，有利于另一个晚到物的情况称为“促进生态位”。在微生物群落中，许多菌株可以代谢其他生物的副产品，这些微生物将大的有机分子分解成更小的分子，使得原本无法获得的营养物变得可用，促进后来微生物群落的建立。早到的物种改变了环境状况(而不是资源水平)以减缓或阻止晚到物种在该系统的建立，为“抑制生态位”。“抑制生态位”由明显竞争或干扰竞争引起。

Mechanisms of priority effects are divided into Niche pre-emption, Niche facilitative modification and Niche inhibitory modification. Niche pre-emption occurs whenan early- arriving organism depletes resources, therebyinhibiting the establishment of a late arriver. Multiplelines of evidence point to niche pre- emption, particularlycompetition for nutrients (exploitative competition),as an important process in microbiome assembly. Niche facilitative modification(facilitation) occurs when an early- arrivingorganism alters the environment in a way that benefitsa later- arriving organism. Facilitation is also commonin microbial communities, where many strainscan metabolize byproducts of other organisms. Inparticular, the ability of arriving microorganisms toestablish can depend on the presence of microorganismsthat have broken down large organic moleculesinto smaller molecules, making otherwise inaccessiblenutrients available. Niche inhibitory modification(inhibition) occurs when an early- arrivingspecies modifies conditions (rather than resource levels)in a way that slows or prevents the establishmentof later- arriving species. Niche inhibitory modificationcan arise through apparent competition or throughinterference competition.

改变单个菌株或整个菌群的到达顺序的实验研究，可以直接检测微生物群落的优先效应。对植物叶际和小鼠肠道微生物组形成的实验分析显示，大多数观察到的优先效应是抑制作用，只有少数菌株受优先效应的影响表现为促进作用。

Experimentalstudies that vary the arrival order of individualstrains or entire consortia can directly measureboth the role of priority effects in communityassembly and the importance of external factors, suchas nutrient availability, for these effects. Experimentalmanipulations of phyllosphere and mouse gut microbiomeassembly showed that most observed priorityeffects were inhibitory, with only a minority of strainsbenefiting from facilitation.

从全面分析的数据集中最能获得真实微生物群落动态，尤其是涉及稀少和未培养生物类群的相互作用。拥有合适的观察数据集，利用统计方法预测哪些类群是值得研究的，并缩小后续实验验证的研究范围。在一定时间范围内对宿主重复采样可以获取单个生物类群的到达时间和在这个系统的维持时间。如果研究队列足够大，单个生物类群在某系统的维持的变化可能与它们到达之前的该系统原有微生物组组成有关。在不同数据集中，抑制性优先效应总是发生在亲缘关系较近的微生物之间，而不是随机发生的。

Fully observational datasets have the highest potentialto capture realistic microbiome dynamics, especiallyinteractions involving rare and/or uncultured taxa.With an appropriate observational dataset, it ispossible to statistically predict which taxa are of interestand narrow the search space for subsequent experimentalvalidation.Repeatedly sampling hosts overtime captures the arrival times and subsequent persistenceof individual taxa.With sufficient cohortsize, the variation in persistence of individual taxa maybe linked to resident microbiome composition beforetheir arrival. Across datasets, candidate inhibitorypriority effects consistently occurred among moreclosely related taxa than expected by chance.

实验室研究和实地调查表明，优先效应是微生物群落组成和功能变化的关键和决定因素。优先效应塑造了微生物群落的形成和稳定性。这表明，在我们开始为人类、牲畜、作物和环境健康重塑微生物群落时，要考虑微生物群落的优先效应。

Laboratory experiments and field surveys point to priorityeffects as key, understudied determinants of microbiomeassembly and function.Overall, the existing data make it clear that priorityeffects shape microbiome assembly and stability. Therefore, priorityeffects should be considered as we begin reshaping microbiomesfor human, livestock, crop and environmentalhealth.

原文链接：https://www.nature.com/articles/s41579-021-00604-w