Abisado Rhea G, Kimbrough John H, McKee Brielle M, Craddock Vaughn D, Smalley Nicole E, Dandekar Ajai A, Chandler Josephine R
Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA.
Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, USA.
Appl Environ Microbiol. 2021 May 26;87(12):e0002921. doi: 10.1128/AEM.00029-21.
The Pseudomonas aeruginosa LasR-LasI (LasR-I) quorum sensing system regulates secreted proteases that can be exploited by cheaters, such as quorum sensing receptor-defective () mutants. mutants emerge in populations growing on casein as a sole source of carbon and energy. These mutants are exploitative cheaters because they avoid the substantial cost of engaging in quorum sensing. Previous studies showed that quorum sensing increases resistance to some antibiotics, such as tobramycin. Here, we show that tobramycin suppressed the emergence of mutants in casein-passaged populations. Several mutations accumulated in those populations, indicating evidence of antibiotic adaptation. We found that mutations in one gene, increased antibiotic resistance and also pleiotropically increased production of a quorum sensing-controlled phenazine, pyocyanin. When passaged on casein, mutants suppressed cheaters in a manner that was tobramycin independent. We found that the mechanism of cheater suppression in mutants relied on pyocyanin, which acts as a policing toxin by selectively blocking growth of cheaters. Thus, tobramycin suppresses mutants through two mechanisms: first, through direct effects on cheaters and, second, by selecting mutations in that suppressed cheating in a tobramycin-independent manner. This work demonstrates how adaptive mutations can alter the dynamics of cooperator-cheater relationships, which might be important for populations adapting to antibiotics during interspecies competition or infections. The opportunistic pathogen Pseudomonas aeruginosa is a model for understanding quorum sensing, a type of cell-cell signaling important for cooperation. Quorum sensing controls production of cooperative goods, such as exoenzymes, which are vulnerable to cheating by quorum sensing-defective mutants. Because uncontrolled cheating can ultimately cause a population to collapse, much focus has been on understanding how P. aeruginosa can control cheaters. We show that an antibiotic, tobramycin, can suppress cheaters in cooperating P. aeruginosa populations. Tobramycin suppresses cheaters directly because the cheaters are more susceptible to tobramycin than cooperators. Tobramycin also selects for mutations in a gene, that suppresses cheaters independent of tobramycin through pleiotropic regulation of a policing toxin, pyocyanin. This work supports the idea that adaptation to antibiotics can have unexpected effects on the evolution of quorum sensing and has implications for understanding how cooperation evolves in dynamic bacterial communities.
铜绿假单胞菌LasR-LasI（LasR-I）群体感应系统调控可被作弊者利用的分泌蛋白酶，比如群体感应受体缺陷（）突变体。在以酪蛋白作为唯一碳源和能源生长的群体中会出现突变体。这些突变体是剥削性作弊者，因为它们避免了参与群体感应的巨大成本。先前的研究表明群体感应会增加对某些抗生素的抗性，比如对妥布霉素的抗性。在此，我们表明妥布霉素抑制了酪蛋白传代群体中突变体的出现。在那些群体中积累了几个突变，这表明存在抗生素适应性的证据。我们发现一个基因中的突变增加了抗生素抗性，并且还多效性地增加了一种群体感应控制的吩嗪——绿脓菌素的产生。当在酪蛋白上传代时，突变体以一种与妥布霉素无关的方式抑制作弊者。我们发现突变体中作弊者抑制机制依赖于绿脓菌素，它通过选择性地阻断作弊者的生长来充当一种监管毒素。因此，妥布霉素通过两种机制抑制突变体：第一，通过对作弊者的直接作用；第二，通过选择基因中的突变，该突变以一种与妥布霉素无关的方式抑制作弊行为。这项工作证明了适应性突变如何能够改变合作者 - 作弊者关系的动态，这对于在种间竞争或感染期间适应抗生素的群体可能很重要。机会致病菌铜绿假单胞菌是理解群体感应的一个模型，群体感应是一种对合作很重要的细胞间信号传导类型。群体感应控制合作产物的产生，比如易受群体感应缺陷突变体作弊影响的胞外酶。由于不受控制的作弊最终可能导致群体崩溃，所以很多研究重点都放在了理解铜绿假单胞菌如何控制作弊者上。我们表明一种抗生素——妥布霉素，可以抑制合作的铜绿假单胞菌群体中的作弊者。妥布霉素直接抑制作弊者，因为作弊者比合作者对妥布霉素更敏感。妥布霉素还会选择一个基因中的突变，该突变通过对一种监管毒素绿脓菌素的多效性调控来抑制与妥布霉素无关的作弊者。这项工作支持了这样一种观点，即对抗生素的适应可能会对群体感应的进化产生意想不到的影响，并且对于理解合作在动态细菌群落中如何进化具有启示意义。
