von Bronk Benedikt, Schaffer Sophia Anna, Götz Alexandra, Opitz Madeleine
Center for NanoScience, Faculty of Physics, Ludwig-Maximilians-Universität München, München, Germany.
PLoS Biol. 2017 May 1;15(5):e2001457. doi: 10.1371/journal.pbio.2001457. eCollection 2017 May.
In phenotypically heterogeneous microbial populations, the decision to adopt one or another phenotype is often stochastically regulated. However, how this stochasticity affects interactions between competing microbes in mixed communities is difficult to assess. One example of such an interaction system is the competition of an Escherichia coli strain C, which performs division of labor between reproducers and self-sacrificing toxin producers, with a toxin-sensitive strain S. The decision between reproduction or toxin production within a single C cell is inherently stochastic. Here, combining experimental and theoretical approaches, we demonstrate that this stochasticity in the initial phase of colony formation is the crucial determinant for the competition outcome. In the initial phase (t < 12h), stochasticity influences the formation of viable C clusters at the colony edge. In the subsequent phase, the effective fitness differences (set primarily by the degree of division of labor in the C strain population) dictate the deterministic population dynamics and consequently competition outcome. In particular, we observe that competitive success of the C strain is only found if (i) a C edge cluster has formed at the end of the initial competition phase and (ii) the beneficial and detrimental effects of toxin production are balanced, which is the case at intermediate toxin producer fractions. Our findings highlight the importance of stochastic processes during the initial phase of colony formation, which might be highly relevant for other microbial community interactions in which the random choice between phenotypes can have long-lasting consequences for community fate.
在表型异质的微生物群体中，采用一种或另一种表型的决定通常受到随机调控。然而，这种随机性如何影响混合群落中竞争性微生物之间的相互作用却难以评估。这样一个相互作用系统的一个例子是大肠杆菌C菌株与毒素敏感的S菌株之间的竞争，C菌株在繁殖者和自我牺牲的毒素产生者之间进行分工。单个C细胞内繁殖或毒素产生之间的决定本质上是随机的。在这里，结合实验和理论方法，我们证明了菌落形成初始阶段的这种随机性是竞争结果的关键决定因素。在初始阶段（t < 12小时），随机性影响菌落边缘活C簇的形成。在随后的阶段，有效的适应性差异（主要由C菌株群体中的分工程度决定）决定了确定性的种群动态，进而决定了竞争结果。特别是，我们观察到只有在以下情况下才会发现C菌株的竞争成功：（i）在初始竞争阶段结束时形成了C边缘簇，以及（ii）毒素产生的有益和有害影响达到平衡，在中等毒素产生者比例的情况下就是如此。我们的研究结果突出了菌落形成初始阶段随机过程的重要性，这可能与其他微生物群落相互作用高度相关，在这些相互作用中，表型之间的随机选择可能对群落命运产生长期影响。
