Jwanoswki Kathleen, Wells Christina, Bruce Terri, Rutt Jennifer, Banks Tabitha, McNealy Tamara L
Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America.
Clemson Light Imaging Facility, Clemson University, Clemson, South Carolina, United States of America.
PLoS One. 2017 May 2;12(5):e0174245. doi: 10.1371/journal.pone.0174245. eCollection 2017.
Legionella pneumophila contaminates man-made water systems and creates numerous exposure risks for Legionnaires' Disease. Because copper/silver ionization is commonly used to control L. pneumophila, its mechanisms of metal response and detoxification are of significant interest. Here we describe an L. pneumophila operon with significant similarity to the GIG operon of Cupriavidus metallidurans. The Legionella GIG operon is present in a subset of strains and has been acquired as part of the ICE-βox 65-kB integrative conjugative element. We assessed GIG promoter activity following exposure of L. pneumophila to multiple concentrations of HAuCl4, CuSO4 and AgNO3. At 37°C, control stationary phase cultures exhibited GIG promoter activity. This activity increased significantly in response to 20 and 50uM HAuCl4 and CuSO4 but not in response to AgNO3. Conversely, at 26°C, cultures exhibited decreased promoter response to copper. GIG promoter activity was also induced by HAuCl4 or CuSO4 during early biofilm establishment at both temperatures. When an L. pneumophila GIG promoter construct was transformed into E. coli DH5α, cultures showed baseline expression levels that did not increase following metal addition. Analysis of L. pneumophila transcriptional regulatory mutants suggested that GIG up-regulation in the presence of metal ions may be influenced by the stationary phase sigma factor, RpoS.
嗜肺军团菌污染人造水系统，并给军团菌病带来诸多暴露风险。由于铜/银离子化常用于控制嗜肺军团菌，其金属反应和解毒机制备受关注。在此，我们描述了一个与金属抗性贪铜菌的GIG操纵子具有显著相似性的嗜肺军团菌操纵子。军团菌GIG操纵子存在于部分菌株中，是作为ICE-βox 65-kB整合接合元件的一部分获得的。我们评估了嗜肺军团菌在暴露于多种浓度的HAuCl4、CuSO4和AgNO3后GIG启动子的活性。在37°C时，对照静止期培养物表现出GIG启动子活性。这种活性在暴露于20和50μM的HAuCl4和CuSO4时显著增加，但对AgNO3无反应。相反，在26°C时，培养物对铜的启动子反应降低。在两个温度下的生物膜早期形成过程中，HAuCl4或CuSO4也诱导了GIG启动子活性。当将嗜肺军团菌GIG启动子构建体转化到大肠杆菌DH5α中时，培养物显示出基线表达水平，在添加金属后并未增加。对嗜肺军团菌转录调控突变体的分析表明，在金属离子存在下GIG的上调可能受静止期σ因子RpoS的影响。
