Kümmerli R, Santorelli L A, Granato E T, Dumas Z, Dobay A, Griffin A S, West S A
Microbial Evolutionary Ecology, Institute of Plant Biology, University of Zürich, Zürich, Switzerland.
Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland.
J Evol Biol. 2015 Dec;28(12):2264-74. doi: 10.1111/jeb.12751. Epub 2015 Sep 28.
The production of beneficial public goods is common in the microbial world, and so is cheating--the exploitation of public goods by nonproducing mutants. Here, we examine co-evolutionary dynamics between cooperators and cheats and ask whether cooperators can evolve strategies to reduce the burden of exploitation, and whether cheats in turn can improve their exploitation abilities. We evolved cooperators of the bacterium Pseudomonas aeruginosa, producing the shareable iron-scavenging siderophore pyoverdine, together with cheats, defective in pyoverdine production but proficient in uptake. We found that cooperators managed to co-exist with cheats in 56% of all replicates over approximately 150 generations of experimental evolution. Growth and competition assays revealed that co-existence was fostered by a combination of general adaptions to the media and specific adaptions to the co-evolving opponent. Phenotypic screening and whole-genome resequencing of evolved clones confirmed this pattern, and suggest that cooperators became less exploitable by cheats because they significantly reduced their pyoverdine investment. Cheats, meanwhile, improved exploitation efficiency through mutations blocking the costly pyoverdine-signalling pathway. Moreover, cooperators and cheats evolved reduced motility, a pattern that likely represents adaptation to laboratory conditions, but at the same time also affects social interactions by reducing strain mixing and pyoverdine sharing. Overall, we observed parallel evolution, where co-existence of cooperators and cheats was enabled by a combination of adaptations to the abiotic and social environment and their interactions.
有益公共物品的产生在微生物世界中很常见，作弊行为也是如此——即不产生公共物品的突变体对公共物品的利用。在这里，我们研究了合作者和作弊者之间的共同进化动态，并探讨合作者是否能够进化出策略来减轻被利用的负担，以及作弊者是否能够反过来提高其利用能力。我们让能够产生可共享的铁载体绿脓菌素的铜绿假单胞菌合作者与绿脓菌素产生有缺陷但摄取能力强的作弊者共同进化。我们发现，在大约150代的实验进化中，56%的重复实验中合作者成功地与作弊者共存。生长和竞争试验表明，对培养基的一般适应和对共同进化对手的特定适应相结合促进了共存。对进化克隆的表型筛选和全基因组重测序证实了这一模式，并表明合作者因显著减少其绿脓菌素投入而变得不易被作弊者利用。与此同时，作弊者通过阻断代价高昂的绿脓菌素信号通路发生突变来提高利用效率。此外，合作者和作弊者的运动性都有所降低，这种模式可能代表了对实验室条件的适应，但同时也通过减少菌株混合和绿脓菌素共享来影响社会互动。总体而言，我们观察到了平行进化，即合作者和作弊者的共存是通过对非生物和社会环境及其相互作用的适应组合实现的。
