Haber Adi, Friedman Sivan, Lobel Lior, Burg-Golani Tamar, Sigal Nadejda, Rose Jessica, Livnat-Levanon Nurit, Lewinson Oded, Herskovits Anat A
Department of Biochemistry, The Bruce and Ruth Rappaport Faculty of Medicine, the Rappaport Institute for Biomedical research, Technion-Israel Institute of Technology, Haifa, Israel.
The Department of Molecular Microbiology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
PLoS Pathog. 2017 Jan 23;13(1):e1006161. doi: 10.1371/journal.ppat.1006161. eCollection 2017 Jan.
The high environmental adaptability of bacteria is contingent upon their ability to sense changes in their surroundings. Bacterial pathogen entry into host poses an abrupt and dramatic environmental change, during which successful pathogens gauge multiple parameters that signal host localization. The facultative human pathogen Listeria monocytogenes flourishes in soil, water and food, and in ~50 different animals, and serves as a model for intracellular infection. L. monocytogenes identifies host entry by sensing both physical (e.g., temperature) and chemical (e.g., metabolite concentrations) factors. We report here that L-glutamine, an abundant nitrogen source in host serum and cells, serves as an environmental indicator and inducer of virulence gene expression. In contrast, ammonia, which is the most abundant nitrogen source in soil and water, fully supports growth, but fails to activate virulence gene transcription. We demonstrate that induction of virulence genes only occurs when the Listerial intracellular concentration of L-glutamine crosses a certain threshold, acting as an on/off switch: off when L-glutamine concentrations are below the threshold, and fully on when the threshold is crossed. To turn on the switch, L-glutamine must be present, and the L-glutamine high affinity ABC transporter, GlnPQ, must be active. Inactivation of GlnPQ led to complete arrest of L-glutamine uptake, reduced type I interferon response in infected macrophages, dramatic reduction in expression of virulence genes, and attenuated virulence in a mouse infection model. These results may explain observations made with other pathogens correlating nitrogen metabolism and virulence, and suggest that gauging of L-glutamine as a means of ascertaining host localization may be a general mechanism.
细菌对环境的高度适应性取决于它们感知周围环境变化的能力。细菌病原体进入宿主会引发突然而剧烈的环境变化，在此期间，成功的病原体能够检测到多个指示宿主定位的参数。兼性人类病原体单核细胞增生李斯特菌在土壤、水和食物中以及约50种不同动物中都能生长，并作为细胞内感染的模型。单核细胞增生李斯特菌通过感知物理（如温度）和化学（如代谢物浓度）因素来识别进入宿主的过程。我们在此报告，L-谷氨酰胺是宿主血清和细胞中丰富的氮源，它作为一种环境指标和毒力基因表达的诱导剂。相比之下，氨是土壤和水中最丰富的氮源，它能充分支持生长，但不能激活毒力基因转录。我们证明，只有当李斯特菌细胞内L-谷氨酰胺浓度超过一定阈值时，毒力基因才会被诱导，这起到了一个开/关开关的作用：当L-谷氨酰胺浓度低于阈值时关闭，当超过阈值时完全开启。要打开这个开关，必须存在L-谷氨酰胺，并且L-谷氨酰胺高亲和力ABC转运蛋白GlnPQ必须处于活跃状态。GlnPQ的失活导致L-谷氨酰胺摄取完全停止，感染巨噬细胞中I型干扰素反应降低，毒力基因表达显著减少，并且在小鼠感染模型中毒力减弱。这些结果可能解释了其他病原体中与氮代谢和毒力相关的观察结果，并表明将L-谷氨酰胺作为确定宿主定位的一种手段可能是一种普遍机制。
