Popat Roman, Harrison Freya, da Silva Ana C, Easton Scott A S, McNally Luke, Williams Paul, Diggle Stephen P
School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry CV4 7AL, UK.
Proc Biol Sci. 2017 Apr 12;284(1852). doi: 10.1098/rspb.2017.0200.
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 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 , 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.
细菌会产生各种各样的胞外产物，这些产物能有利地改变其生存环境并提高其适应性。这些产物通常被称为“公共物品”，因为个体生产它们成本高昂，且可能被非生产者（作弊者）利用。围绕公共物品的冲突结果取决于当前环境以及竞争个体的表型。许多细菌物种利用群体感应（QS）信号分子来调节公共物品的产生。因此，群体感应决定了个体的合作表型，并影响围绕公共物品的冲突。除了其调节功能外，许多群体感应分子还具有直接改变当前环境的其他特性。这就导致群体感应分子可能通过非信号效应间接影响围绕公共物品的冲突，而此前尚未探讨过这对社会竞争的影响。群体感应信号分子2-庚基-3-羟基-4（1H）-喹诺酮（PQS）是一种强大的铁螯合剂，可引发铁饥饿反应。在此，我们表明PQS刺激铁载体清除铁的协同产量呈浓度依赖性增加，导致不产铁载体的作弊者的相对适应性增加。这可能是由于产铁载体细胞的铁载体输出成本增加，以及生产者和作弊者共同获得的共享利益同时增加所致。尽管PQS对……可能是一种有益的信号分子，但我们的数据表明，它也可能使产铁载体的群体容易受到作弊菌株竞争的影响。更普遍地说，我们的结果表明，一种社会性状的产生可以间接影响另一种社会性状的成本和收益。
