Cooperation and Cheating in Bacterial Quorum Sensing

科学研究。在了解细菌如何沟通和合作以执行各种多细胞行为的机制方面，已经有了大量的研究。直到最近，微生物学家才开始从社会进化的角度研究这些行为。Schuster博士的长期目标是整合机制和进化方法来研究交流，也称为群体感应（QS），以及模型细菌铜绿假单胞菌的合作。铜绿假单胞菌通过扩散酰基-高丝氨酸内酯（酰基- hsl）信号来协调数百个基因的表达，其中许多基因编码细胞外因子。酰基- hsl QS是细菌中广泛存在的一种现象，它调节着多种群体行为，如产光、毒力和生物膜的形成。该项目的具体目标是对新的社会行为形式进行全面的表征。最初，重点将放在最近发现的信号盲强制性欺骗和重新进化的合作现象上，这是Schuster小组在对铜绿假单胞菌的实验进化研究中发现的。有义务的作弊者不会为群体控制的公共产品的生产做出贡献，因为他们在编码中央QS调节器的基因中携带了功能丧失的突变。这种突变体已经从自然环境中分离出来，这表明在体内也会出现作弊者。据预测，从作弊者中重新进化出来的合作者在基因组的其他地方会发生突变，从而恢复依赖于qs的表型。人们对这种从强制性生活方式向自主生活方式转变的遗传基础知之甚少。重新进化的合作者基因组中的候选突变指向QS基因表达的新调控机制。该项目的具体目标是：(1)描述导致从欺骗者转变为合作者的突变和潜在的分子机制，(2)筛选环境中铜绿假单胞菌分离物中存在的社会突变，并确定其在种群中的频率，以及(3)描述在社会和非社会条件下从欺骗者转变为合作者的进化适应性和合作行为。这项研究与许多依赖社会特征获得进化成功的细菌的进化有关，并对我们理解所有生命领域合作行为的进化具有重要意义。教育的影响。所描述的项目为学生提供了良好的教育机会。Schuster博士已经并将继续在实验室培养研究生和本科生。舒斯特博士还将通过俄勒冈州立大学的一个既定项目为高中生提供教育机会。他发现，在微生物问题的研究中结合进化概念大大提高了学生的好奇心和兴趣。大多数实验在概念上和技术上都是直截了当的，特别适合高中生和本科生参与科学过程。

Scientific research. There has been an explosion of research directed at understanding the mechanisms of how bacteria communicate and cooperate to perform a variety of multicellular behaviors. Not until very recently have microbiologists also begun to investigate these behaviors from the perspective of social evolution. Dr. Schuster's long-term goal is to integrate mechanistic and evolutionary approaches to investigate communication, also termed quorum sensing (QS), and cooperation in the model bacterium Pseudomonas aeruginosa. P. aeruginosa communicates via diffusible acyl-homoserine lactone (acyl-HSL) signals to coordinate the expression of hundreds of genes, many of which encode extracellular factors. Acyl-HSL QS is a widespread phenomenon in bacteria and regulates diverse group behaviors such as light production, virulence, and biofilm formation. The specific objective of this project is to conduct a comprehensive characterization of novel forms of social behavior. Initially, the focus will be on the recently discovered signal-blind obligate cheating and re-evolved cooperation phenomenon that the Schuster group identified during an experimental evolution study of P. aeruginosa. The obligate cheaters do not contribute to the production of quorum-controlled public goods because they harbor a loss-of-function mutation in the gene encoding the central QS regulator. Such mutants have been isolated from natural environments suggesting that cheaters arise also in vivo. The re-evolved cooperators emerged from cheaters are predicted to harbor mutations elsewhere in the genome that restore QS-dependent phenotypes. Very little is known about the genetic basis of such transitions from an obligate to an autonomous life style. Candidate mutations in the genome of a re-evolved cooperator point towards a novel regulatory mechanism of QS gene expression. The specific aims of this project are to (1) characterize the mutation(s) and underlying molecular mechanisms responsible for the cheater-to-cooperator conversion, (2) screen environmental P. aeruginosa isolates for the presence of social mutations and determine their frequency within the population, and (3) characterize evolutionary fitness and cooperative behavior of the cheater-turned-cooperator under social and asocial conditions. This research is relevant to the evolution of many bacteria that rely on social traits for evolutionary success, and has important implications for our understanding of the evolution of cooperative behavior across all domains of life. Educational impact. The described project provides excellent educational opportunities for students. Dr. Schuster has and will continue to train graduate and undergraduate students in the laboratory. Dr. Schuster will also provide educational opportunities for high-school students through an established program at Oregon State University. He has found that the incorporation of evolutionary concepts in the study of microbiological problems greatly enhances student curiosity and interest. Most experiments are conceptually and technically straight-forward and are particularly well suited for the engagement of high-school and undergraduate students in the scientific process.