Bruger Eric L, Waters Christopher M
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, USA.
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, USA
Appl Environ Microbiol. 2016 Oct 27;82(22):6498-6506. doi: 10.1128/AEM.01945-16. Print 2016 Nov 15.
Communication has been suggested as a mechanism to stabilize cooperation. In bacteria, chemical communication, termed quorum sensing (QS), has been hypothesized to fill this role, and extracellular public goods are often induced by QS at high cell densities. Here we show, with the bacterium Vibrio harveyi, that QS provides strong resistance against invasion of a QS defector strain by maximizing the cellular growth rate at low cell densities while achieving maximum productivity through protease upregulation at high cell densities. In contrast, QS mutants that act as defectors or unconditional cooperators maximize either the growth rate or the growth yield, respectively, and thus are less fit than the wild-type QS strain. Our findings provide experimental evidence that regulation mediated by microbial communication can optimize growth strategies and stabilize cooperative phenotypes by preventing defector invasion, even under well-mixed conditions. This effect is due to a combination of responsiveness to environmental conditions provided by QS, lowering of competitive costs when QS is not induced, and pleiotropic constraints imposed on defectors that do not perform QS.
Cooperation is a fundamental problem for evolutionary biology to explain. Conditional participation through phenotypic plasticity driven by communication is a potential solution to this dilemma. Thus, among bacteria, QS has been proposed to be a proximate stabilizing mechanism for cooperative behaviors. Here, we empirically demonstrate that QS in V. harveyi prevents cheating and subsequent invasion by nonproducing defectors by maximizing the growth rate at low cell densities and the growth yield at high cell densities, whereas an unconditional cooperator is rapidly driven to extinction by defectors. Our findings provide experimental evidence that QS regulation prevents the invasion of cooperative populations by QS defectors even under unstructured conditions, and they strongly support the role of communication in bacteria as a mechanism that stabilizes cooperative traits.
通讯被认为是一种稳定合作的机制。在细菌中，化学通讯，即群体感应（QS），被假定发挥这一作用，细胞外公共物品通常在高细胞密度时由群体感应诱导产生。在这里，我们以哈氏弧菌为例表明，群体感应通过在低细胞密度时最大化细胞生长速率，同时在高细胞密度时通过上调蛋白酶实现最大生产力，从而对群体感应缺陷菌株的入侵提供强大抗性。相比之下，作为缺陷者或无条件合作者的群体感应突变体分别最大化生长速率或生长产量，因此比野生型群体感应菌株适应性更差。我们的研究结果提供了实验证据，表明由微生物通讯介导的调控可以优化生长策略，并通过防止缺陷者入侵来稳定合作表型，即使在充分混合的条件下也是如此。这种效应是由于群体感应提供的对环境条件的响应、未诱导群体感应时竞争成本的降低以及对不进行群体感应的缺陷者施加的多效性限制共同作用的结果。
合作是进化生物学需要解释的一个基本问题。通过通讯驱动的表型可塑性进行条件性参与是解决这一困境的一个潜在方案。因此，在细菌中，群体感应被认为是合作行为的一种直接稳定机制。在这里，我们通过实验证明，哈氏弧菌中的群体感应通过在低细胞密度时最大化生长速率和在高细胞密度时最大化生长产量来防止欺骗以及随后非产生型缺陷者的入侵，而无条件合作者会迅速被缺陷者驱向灭绝。我们的研究结果提供了实验证据，表明群体感应调控即使在非结构化条件下也能防止群体感应缺陷者入侵合作群体，并且它们有力地支持了细菌中通讯作为一种稳定合作性状机制的作用。
