1College of William & Mary, Department of Biology, Integrated Science Center Rm 3035, 540 Landrum Dr Williamsburg, VA 23185, USA.
2Department of Ecology, Evolution, and Behavior, University of Minnesota-Twin Cities, 100 Ecology Building, 1987 Upper Buford Circle, Saint Paul, MN 55108, USA.
Microbiology (Reading). 2019 Feb;165(2):174-187. doi: 10.1099/mic.0.000756. Epub 2019 Jan 16.
For micro-organisms cycling between free-living and host-associated stages, where reproduction occurs in both of these lifestyles, an interesting inquiry is whether evolution during the free-living stage can be positively pleiotropic to microbial fitness in a host environment. To address this topic, the squid host Euprymna tasmanica and the marine bioluminescent bacterium Vibrio fischeri were utilized. Microbial ecological diversification in static liquid microcosms was used to simulate symbiont evolution during the free-living stage. Thirteen genetically distinct V. fischeri strains from a broad diversity of ecological sources (e.g. squid light organs, fish light organs and seawater) were examined to see if the results were reproducible in many different genetic settings. Genetic backgrounds that are closely related can be predisposed to considerable differences in how they respond to similar selection pressures. For all strains examined, new mutations with striking and facilitating effects on host colonization arose quickly during microbial evolution in the free-living stage, regardless of the ecological context under consideration for a strain's genetic background. Microbial evolution outside a host environment promoted host range expansion, improved host colonization for a micro-organism, and diminished the negative correlation between biofilm formation and motility.
对于在自由生活和宿主相关阶段之间循环的微生物，其中繁殖发生在这两种生活方式中，一个有趣的探究是，在自由生活阶段的进化是否可以对微生物在宿主环境中的适应性产生积极的多效性。为了解决这个问题，利用了鱿鱼宿主 Euprymna tasmanica 和海洋发光细菌 Vibrio fischeri。利用静态液体微宇宙中的微生物生态多样化来模拟自由生活阶段共生体的进化。从广泛的生态来源（例如鱿鱼发光器官、鱼类发光器官和海水）中检查了 13 种具有不同遗传背景的独特 V. fischeri 菌株，以观察它们在许多不同遗传背景下的结果是否具有可重复性。遗传背景密切相关的菌株可能容易受到相似选择压力的影响而产生很大的差异。对于所有检查的菌株，新的突变在自由生活阶段的微生物进化过程中迅速出现，对宿主定殖具有显著促进作用，无论考虑菌株遗传背景的生态背景如何。在宿主环境之外的微生物进化促进了宿主范围的扩大，提高了微生物对宿主的定殖能力，并降低了生物膜形成和运动之间的负相关关系。
