College of Life and Environmental Sciences, Environment and Sustainability Institute, University of Exeter, Penryn, United Kingdom.
Bioimaging Center, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom.
mBio. 2023 Apr 25;14(2):e0046023. doi: 10.1128/mbio.00460-23. Epub 2023 Apr 6.
Bacteriophages ("phages") are hypothesized to be key drivers of bacterial population dynamics, driving microbial community composition, but empirical support for this is mixed. One reason why phages may have a less-than-expected impact on community composition is that many different phages and other mobile genetic elements (MGEs) interact with each bacterium. For instance, the same phage may have higher or lower costs to different bacterial strains or species. Assuming that resistance or susceptibility to MGE infection is not consistent across all MGEs, a simple prediction is that the net effect of MGEs on each bacterial taxon may converge with an increasing number of interactions with different MGEs. We formalized this prediction using population dynamics simulations and then carried out experiments using three bacterial species, one generalist conjugative plasmid, and three species-specific phages. While the presence of only phages or only the plasmid altered community structure, these differential effects on community structure canceled out when both were together. The effects of MGEs were largely indirect and could not be explained by simple pairwise bipartite interactions (i.e., between each MGE and each bacterial species). Our results suggest that the effects of MGEs may be overestimated by studies that focus on a single MGE and not on interactions among multiple MGEs. While bacteriophages ("phages") are often cited as some of the key drivers of microbial diversity, evidence for this is greatly mixed. We demonstrate, and experimentally, that the impact of phages, an example of a mobile genetic element (MGE), on community structure can diminish with increasing MGE diversity. This is because MGEs can have diverse effects on host fitness, and therefore as diversity increases, their individual effects cancel out, returning communities back to an MGE-free state. In addition, interactions in mixed-species and MGE communities could not be predicted from simple pairwise interactions, highlighting the difficulty in generalizing a MGE's effect from pairwise studies.
噬菌体（“phages”）被认为是细菌种群动态的关键驱动因素，它们影响着微生物群落的组成，但目前对这一观点的实证支持还存在分歧。噬菌体对群落组成的影响可能不如预期的原因之一是，许多不同的噬菌体和其他可移动遗传因子（MGEs）与每一种细菌相互作用。例如，同一种噬菌体对不同的细菌菌株或物种可能有更高或更低的成本。假设对 MGE 感染的抗性或敏感性在所有 MGE 中并不一致，那么一个简单的预测是，随着与不同 MGE 的相互作用数量的增加，MGE 对每个细菌分类群的净效应可能会趋同。我们使用种群动态模拟对这一预测进行了形式化，并使用三种细菌、一种普遍的接合质粒和三种种特异性噬菌体进行了实验。虽然只有噬菌体或只有质粒的存在会改变群落结构，但当两者同时存在时，它们对群落结构的这种差异影响会相互抵消。MGE 的影响主要是间接的，不能用简单的双二元相互作用（即每个 MGE 与每个细菌物种之间的相互作用）来解释。我们的研究结果表明，那些只关注单一 MGE 而不关注多个 MGE 之间相互作用的研究可能高估了 MGE 的影响。虽然噬菌体通常被认为是微生物多样性的关键驱动因素之一，但这方面的证据却存在很大的差异。我们通过理论和实验证明，噬菌体（一种可移动遗传因子（MGE）的一个例子）对群落结构的影响会随着 MGE 多样性的增加而减弱。这是因为 MGE 对宿主适应性有不同的影响，因此随着多样性的增加，它们的个体影响会相互抵消，使群落回归到无 MGE 的状态。此外，混合物种和 MGE 群落中的相互作用不能从简单的二元相互作用中预测出来，这突出了从二元研究中推广 MGE 效应的困难。
