Data from: The physical boundaries of public goods cooperation between surface-attached bacterial cells

Bacteria secrete a variety of compounds important for nutrient scavenging, competition mediation and infection establishment. While there is a general consensus that secreted compounds can be shared and therefore have social consequences for the bacterial collective, we know little about the physical limits of such bacterial social interactions. Here, we address this issue by studying the sharing of iron-scavenging siderophores between surface-attached microcolonies of the bacterium Pseudomonas aeruginosa. Using single-cell fluorescent microscopy, we show that siderophores, secreted by producers, quickly reach non-producers within a range of 100 μm, and significantly boost their fitness. Producers in turn respond to variation in sharing efficiency by adjusting their pyoverdine investment levels. These social effects wane with larger cell-to-cell distances and on hard surfaces. Thus, our findings reveal the boundaries of compound sharing, and show that sharing is particularly relevant between nearby yet physically separated bacteria on soft surfaces, matching realistic natural conditions such as those encountered in soft tissue infections.

细菌可分泌多种化合物，这些化合物在营养获取、竞争调控与感染建立过程中发挥关键作用。尽管学界普遍认为分泌的化合物可被共享，进而对细菌群体产生社会性影响，但目前我们对这类细菌社会互动的物理边界仍知之甚少。本研究以铜绿假单胞菌（Pseudomonas aeruginosa）附着于表面的微菌落间的铁载体（siderophore）共享行为为研究对象，以此探讨这一科学问题。借助单细胞荧光显微镜技术，我们发现生产者菌株分泌的铁载体可在100微米范围内快速扩散至非生产者菌株，并显著提升后者的适应度。生产者菌株可通过调整其绿脓菌素（pyoverdine）的资源投入水平，对共享效率的变化做出响应。这类社会效应会随细胞间距增大以及在硬质表面环境中逐渐减弱。综上，我们的研究结果揭示了化合物共享的边界条件，并证实共享行为在软质表面上彼此邻近但物理分离的细菌之间尤为重要，这与软组织感染等真实自然环境中的情况相符。