Emory University, Department of Biology, Atlanta, GA, United States.
New College of Florida, Department of Natural Sciences, Sarasota, FL, United States.
Evolution. 2023 Nov 2;77(11):2512-2521. doi: 10.1093/evolut/qpad173.
The impacts of host-associated microbes on their hosts vary along a continuum of antagonistic, neutral, and beneficial interactions. Transmission mode is predicted to contribute to transitions along the continuum by altering opportunities for the alignment of host and microbe fitness interests. Under vertical transmission, microbial evolution is tightly coupled to the host environment, which may facilitate fitness alignment. In contrast, environmentally transmitted microbes spend time in the external environment, outside of hosts, partially decoupling their evolution from the host. This decoupling may misalign host and microbe fitness interests, potentially favoring antagonistic microbial traits. Here, we tested whether transmission environment alters microbial evolution by manipulating the interaction between a commensal Serratia marcescens bacteria and their insect host Anasa tristis, which is the primary vector of these bacteria into plants, where they cause disease. We experimentally evolved S. marcescens through several selection environments. The bacteria were passaged between A. tristis hosts, between A. tristis hosts and soil, through soil, or through standard culture media. We observed rapid evolution of virulence toward hosts across treatments when bacterial evolution occurred within the host environment, indicating that direct host-to-host transmission can increase opportunities for microbes to adapt to hosts and evolve antagonistic traits.
宿主相关微生物对宿主的影响沿着敌对、中立和有益互动的连续体变化。传播方式预计通过改变宿主和微生物适应利益的一致性机会，有助于沿着连续体转变。在垂直传播中，微生物进化与宿主环境紧密结合，这可能促进适应。相比之下，环境传播的微生物在宿主外的外部环境中度过时间，部分将其进化与宿主分离。这种解耦可能会使宿主和微生物的适应利益不一致，从而有利于微生物的拮抗特性。在这里，我们通过操纵共生细菌 S. marcescens 与其昆虫宿主 Anasa tristis 之间的相互作用来测试传播环境是否会改变微生物的进化，A. tristis 是这些细菌进入植物的主要载体，在植物中它们会引起疾病。我们通过几种选择环境对 S. marcescens 进行了实验进化。细菌在 A. tristis 宿主之间、A. tristis 宿主和土壤之间、通过土壤或通过标准培养基之间传递。当细菌在宿主环境中进化时，我们观察到对宿主的毒力在处理过程中迅速进化，这表明直接的宿主间传播可以增加微生物适应宿主和进化拮抗特性的机会。
