Cruz Renae L, Freeman Tiia S, Asfahl Kyle L, Smalley Nicole E, Dandekar Ajai A
Department of Microbiology, University of Washington, Seattle, Washington, USA.
Department of Medicine, University of Washington, Seattle, Washington, USA.
J Bacteriol. 2025 Jan 31;207(1):e0034424. doi: 10.1128/jb.00344-24. Epub 2024 Dec 13.
uses quorum sensing (QS) to regulate the expression of dozens of genes, many of which encode shared products, called "public goods." possesses two complete acyl-homoserine lactone (AHL) QS circuits: the LasR-I and RhlR-I systems. Canonically, these systems are hierarchically organized: RhlR-I activity depends on LasR-I activation. However, in contrast to laboratory strains, isolates from people with cystic fibrosis can engage in AHL QS using only the transcription factor RhlR. In these isolates, RhlR regulates AHL QS and the production of secreted public goods, such as the exoprotease elastase, which are accessible to both producing and non-producing cells. When strains that use LasR to regulate elastase production are grown on casein as the sole carbon and energy source, LasR-null mutant "cheaters" commonly arise in populations due to a selective growth advantage. We asked if these social dynamics might differ in "RhlR cooperators": populations that use RhlR, not LasR, to regulate public goods. We passaged RhlR cooperators from several genetic backgrounds in casein broth. We found that cheaters emerged among most RhlR cooperators. However, in one isolate background, E90, RhlR-null mutants were dramatically outcompeted by RhlR cooperators. In this background, the mechanism by which RhlR mutants are outcompeted by RhlR cooperators is AHL-dependent and occurs in stationary phase but is not the same as previously described "policing" mechanisms. Our data suggest that cheating, or the lack thereof, does not explain the lack of RhlR mutants observed in most infection environments.IMPORTANCEQuorum sensing (QS) mutants arise in a variety of populations of bacteria, but mutants of the gene encoding the transcription factor RhlR in appear to be infrequent. Our work provides insight on the mechanisms through which RhlR-mediated cooperation is maintained in a LasR-null population of . Characterizing the selective pressure(s) that disfavor mutations from occurring in RhlR may enhance our understanding of evolution in chronic infections and potentially guide the development of therapeutics targeting the RhlR-I QS circuit.
利用群体感应（QS）来调控数十个基因的表达，其中许多基因编码共享产物，即所谓的“公共物品”。它拥有两个完整的酰基高丝氨酸内酯（AHL）QS回路：LasR-I和RhlR-I系统。通常情况下，这些系统是分层组织的：RhlR-I的活性依赖于LasR-I的激活。然而，与实验室菌株不同，从囊性纤维化患者中分离出的菌株仅使用转录因子RhlR就能参与AHL QS。在这些分离株中，RhlR调控AHL QS以及分泌性公共物品的产生，比如外切蛋白酶弹性蛋白酶，产生和不产生该酶的细胞都能获取。当使用LasR来调控弹性蛋白酶产生的菌株在以酪蛋白作为唯一碳源和能源的培养基上生长时，由于选择性生长优势，LasR基因缺失的突变“欺骗者”通常会在群体中出现。我们想知道在“RhlR合作者”（即使用RhlR而非LasR来调控公共物品的群体）中这些社会动态是否会有所不同。我们将来自几种遗传背景的RhlR合作者在酪蛋白肉汤中传代培养。我们发现大多数RhlR合作者群体中都出现了欺骗者。然而，在一个分离株背景E90中，RhlR基因缺失的突变体被RhlR合作者显著淘汰。在这个背景下，RhlR突变体被RhlR合作者淘汰的机制依赖于AHL，且发生在稳定期，但与之前描述的“监管”机制不同。我们的数据表明，欺骗现象的有无并不能解释在大多数感染环境中观察到的RhlR突变体缺失的原因。重要性群体感应（QS）突变体在各种细菌群体中都会出现，但编码转录因子RhlR的基因在中的突变体似乎很少见。我们的工作深入了解了在LasR缺失的群体中RhlR介导的合作得以维持的机制。确定不利于RhlR发生突变的选择压力可能会增进我们对慢性感染中进化的理解，并有可能指导针对RhlR-I QS回路的治疗方法的开发。
