Data from: Co-evolutionary dynamics between public good producers and cheats in the bacterium Pseudomonas aeruginosa

The production of beneficial public goods is common in the microbial world, and so is cheating – the exploitation of public goods by non-producing 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 re-sequencing 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.

微生物世界中，有益公共物品的产生极为普遍，而“欺骗”行为（即不产生公共物品的突变体对其进行剥削）也同样常见。本研究聚焦于合作者与欺骗者之间的共进化动力学，旨在探究合作者能否演化出降低剥削负担的策略，以及欺骗者是否能够进一步提升其剥削能力。我们以铜绿假单胞菌（*Pseudomonas aeruginosa*）的合作菌株为研究对象，该菌株可产生可共享的夺铁型铁载体（siderophore）绿脓菌素（pyoverdine）；同时设置欺骗菌株，这类菌株无法合成绿脓菌素，但摄取铁载体的能力完好。在约150代的实验进化过程中，56%的重复实验组实现了合作者与欺骗者的稳定共存。生长与竞争实验表明，共存现象的维持依赖于两类适应性的共同作用：一是对培养基的一般性适应，二是针对共进化对手的特异性适应。对进化后克隆的表型筛选与全基因组重测序结果验证了这一结论，结果显示合作者的可剥削性降低，原因是其显著减少了绿脓菌素的合成投入。与此同时，欺骗者通过突变阻断了耗能的绿脓菌素信号通路，从而提升了其剥削效率。此外，合作者与欺骗者均演化出了运动能力下降的表型，这一特征大概率是对实验室培养条件的适应，但同时也通过减少菌株混合与绿脓菌素共享，影响了群体社会互动。综上，本研究观察到平行进化现象：合作者与欺骗者的共存，是通过对非生物环境、社会环境及其交互作用的多重适应共同实现的。