咖啡环中的生命：蒸发驱动的密度梯度如何决定细菌间竞争的结果
Life in the coffee-ring: how evaporation-driven density gradients dictate the outcome of inter-bacterial competition
摘要：
当一滴水变干时，它通常会留下一个环形的污点，这是一种普遍存在的现象，被称为咖啡环效应。当液体含有悬浮的微生物时也会发生这种情况;蒸发使环中的细胞浓度高于液滴内部。使用生物膜实验和元胞自动机模拟，我们表明，咖啡环效应所产生的物理结构可以显着改变细菌间竞争的结果。我们使用两种$\textit{Vibrio cholerae}$菌株进行实验研究，这两种菌株使用称为6型分泌系统的接触依赖性杀伤机制进行竞争。通过创造一个不均匀的密度分布，咖啡环效应改变了竞争的结果：在低密度内部获胜的细菌菌株在密度更高的环中失败。通过模拟实验确定的密度分布参数，我们概括了我们的实验结果。我们研究了$\textit{V. cholerae}$菌株的频率、其杀死竞争者的相对功效以及液滴中细胞的初始浓度在确定竞争结果中的作用。通过从单个细胞相互作用到菌株频率的整体变化，我们的工作证明了咖啡环效应如何在构建微生物群落中发挥重要作用，间接推动群落组成的生态变化。
英文摘要：
When a drop dries, it often leaves a ring-shaped stain through a ubiquitous phenomenon known as the coffee-ring effect. This also occurs when the liquid contains suspended microbes; evaporation leaves cells at higher concentrations in the ring than the drop interior. Using biofilm experiments and cellular automata simulations, we show that the physical structure created by the coffee-ring effect can dramatically alter the outcome of inter-bacterial competition. We experimentally study this effect using two strains of $\textit{Vibrio cholerae}$ that compete using a contact-dependent killing mechanism termed the type 6 secretion system. By creating a heterogeneous density profile, the coffee-ring effect changes the outcome of competition: the bacterial strain that wins in the low-density interior loses in the far denser ring. Through simulations parameterized with experimentally-determined density profiles, we recapitulate our experimental findings. We examine the role of a $\textit{V. cholerae}$ strain's frequency, its relative efficacy at killing competitors, and the initial concentration of cells in the droplet in determining the outcome of competition. By scaling from individual cellular interactions to overall changes in strain frequency, our work demonstrates how the coffee-ring effect plays a powerful role in structuring microbial communities, indirectly driving ecological changes in community composition.
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