Data from: Environmental modification via a quorum sensing molecule influences the social landscape of siderophore production

Bacteria produce a wide variety of exoproducts that favourably modify their environment and increase their fitness. These are often termed ‘public goods’ because they are costly for individuals to produce and can be exploited by non-producers (cheats). The outcome of conflict over public goods is dependent upon the prevailing environment and the phenotype of the individuals in competition. Many bacterial species use quorum sensing (QS) signalling molecules to regulate the production of public goods. QS, therefore, determines the cooperative phenotype of individuals, and influences conflict over public goods. In addition to their regulatory functions, many QS molecules have additional properties that directly modify the prevailing environment. This leads to the possibility that QS molecules could influence conflict over public goods indirectly through non-signalling effects, and the impact of this on social competition has not previously been explored. The Pseudomonas aeruginosa QS signal molecule PQS is a powerful chelator of iron which can cause an iron starvation response. Here, we show that PQS stimulates a concentration-dependent increase in the cooperative production of iron scavenging siderophores, resulting in an increase in the relative fitness of non-producing siderophore cheats. This is likely due to an increased cost of siderophore output by producing cells and a concurrent increase in the shared benefits, which accrue to both producers and cheats. Although PQS can be a beneficial signalling molecule for P. aeruginosa, our data suggest that it can also render a siderophore-producing population vulnerable to competition from cheating strains. More generally, our results indicate that the production of one social trait can indirectly affect the costs and benefits of another social trait.细菌可产生种类繁多的胞外产物，这类产物可优化自身生存环境并提升个体适应度。这类产物常被称为“公共物品（public goods）”：其合成对单个细菌个体而言存在能量成本，且可被不产生该类产物的个体（即欺骗者（cheats））所利用。公共物品生产相关的冲突结局，取决于当前所处环境以及竞争个体的表型。 诸多细菌物种借助群体感应（quorum sensing，QS）信号分子调控公共物品的合成。因此，群体感应决定了个体的合作型表型，并影响公共物品生产相关的冲突过程。 除调控功能外，诸多群体感应信号分子还具备直接改变所处环境的额外特性。这意味着群体感应信号分子可通过非信号效应间接影响公共物品生产相关的冲突，而该效应对社会竞争的影响此前尚未被探究。 铜绿假单胞菌（Pseudomonas aeruginosa）的群体感应信号分子PQS是一种强效铁螯合剂，可引发铁饥饿应答反应。本研究显示，PQS可通过浓度依赖的方式促进铁载体（siderophores）的合作型合成，进而提升不产铁载体的欺骗型菌株的相对适应度。该现象大概率源于：产铁载体的菌株的铁载体合成成本上升，同时共享收益（生产者与欺骗型菌株均可获取该收益）同步增加。 尽管PQS对铜绿假单胞菌而言可作为有益的信号分子，但本研究数据显示，其同时也会使产铁载体的菌群群体面临欺骗型菌株的竞争威胁。从更广泛的视角来看，本研究结果表明，某一社会性状的合成可间接影响另一社会性状的成本与收益。