Optimal Response to Quorum-Sensing Signals Varies in Different Host Environments with Different Pathogen Group Size.
Optimal Response to Quorum-Sensing Signals Varies in Different Host Environments with Different Pathogen Group Size.
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在具有不同病原体群大小的不同宿主环境中，对群体感应信号的最佳响应有所不同。
作者：
Zhou L
基因表达的主要调控因子（如群体感应系统）中遗传变异的持久性很难解释。在这里，我们研究了革兰氏阳性细菌中多态群体感应盛行的两种假设，即使用不同的信号/受体对（“表型”）来调节相同的功能。首先，表现型之间的社会互动或“兼性欺骗”可能有利于利用他人信号的罕见变异。其次，不同的表现型可能会增加在不同环境中的适应性。我们在无脊椎病原体苏云金芽孢杆菌中评估了这些假设，使用在共同遗传背景中表达的三种表型。同时性欺骗可能发生在混合良好的寄主匀浆中，前提是竞争表型之间存在最小的串扰。然而，当静态培养或自然口腔感染的空间结构增加时，共同表型具有更高的适应性，同时性欺骗不会发生。环境依赖适应度理论得到了明确支持；表现型在对信号的反应和平均竞争适合度方面各不相同。值得注意的是，竞争适应度随群体规模而变化。群体感应的典型社会进化模型预测在较大的群体规模下对信号的反应更高，与之相反，对信号反应最高的表型在较小的宿主中表现最好，因为感染的病原体群体规模较小。在这个系统中，低信号丰度似乎限制了宿主的适应性，而对信号的最佳响应水平在不同的宿主环境中是不同的。群落感知描述了微生物根据当地种群大小改变基因调控的能力。一些成功的理论认为，这是一种合作形式，也就是说，只有当有足够的细菌生产相同的产品时，对共享产品的投资才值得。这一理论可以解释革兰氏阳性菌（如芽孢杆菌和葡萄球菌）这些信号系统的遗传多样性。稀有基因型可能获得的优势（它们可以利用它们更常见的邻居的产物）可以解释为什么不同的基因型可以共存。我们表明，虽然这些社会互动可以在简单的实验室实验中发生，但它们不会发生在使用无脊椎病原体苏云金芽孢杆菌的自然感染中。相反，我们的结果表明，不同的基因型适应不同大小的宿主。总的来说，社会模型不容易应用于这个系统，这意味着需要对这种形式的群体感应进行不同的解释。
The persistence of genetic variation in master regulators of gene expression, such as quorum-sensing systems, is hard to explain. Here, we investigated two alternative hypotheses for the prevalence of polymorphic quorum sensing in Gram-positive bacteria, i.e., the use of different signal/receptor pairs (‘pherotypes’) to regulate the same functions. First, social interactions between pherotypes or ‘facultative cheating’ may favor rare variants that exploit the signals of others. Second, different pherotypes may increase fitness in different environments. We evaluated these hypotheses in the invertebrate pathogen Bacillus thuringiensis, using three pherotypes expressed in a common genetic background. Facultative cheating could occur in well-mixed host homogenates provided there was minimal cross talk between competing pherotypes. However, facultative cheating did not occur when spatial structure was increased in static cultures or in naturalistic oral infections, where common pherotypes had higher fitness. There was clear support for environment-dependent fitness; pherotypes varied in responsiveness to signals and in mean competitive fitness. Notably, competitive fitness varied with group size. In contrast to typical social evolution models of quorum sensing which predict higher response to signal at larger group size, the pherotype with highest responsiveness to signals performed best in smaller hosts where infections have a lower pathogen group size. In this system, low signal abundance appears to limit fitness in hosts, while the optimal level of response to signals varies in different host environments.IMPORTANCEQuorum sensing describes the ability of microbes to alter gene regulation according to their local population size. Some successful theory suggests that this is a form of cooperation, namely, investment in shared products is only worthwhile if there are sufficient bacteria making the same product. This theory can explain the genetic diversity in these signaling systems in Gram-positive bacteria, such asBacillusandStaphylococcussp. The possible advantages gained by rare genotypes (which can exploit the products of their more common neighbors) could explain why different genotypes can coexist. We show that while these social interactions can occur in simple laboratory experiments, they do not occur in naturalistic infections using an invertebrate pathogen, Bacillus thuringiensis. Instead, our results suggest that different genotypes are adapted to differently sized hosts. Overall, social models are not easily applied to this system, implying that a different explanation for this form of quorum sensing is required.