伯氏疏螺旋体需经历鼠和鹿等动物、蜱才能完成自然感染循环。近年文献报道甘油和葡萄糖分别是蜱或哺乳类宿主体内伯氏疏螺旋体主要碳源，故必须碳源利用切换才能在不同宿主中生存，但机制不明。我们前期研究发现伯氏疏螺旋体c-di-GMP合成酶Rrp1、c-di-GMP结合蛋白PlzA和BB0693基因产物阻遏蛋白与glpFKD甘油代谢操纵子表达调控有关。本项目拟确定伯氏疏螺旋体RP0693阻遏蛋白与glpFKD甘油代谢操纵子5’-UTR顺式转录调控元件结合后抑制glpFKD操纵子表达、Rrp1合成的c-di-GMP与PlzA结合后抑制阻遏蛋白下调glpFKD操纵子表达、3-磷酸甘油或6-磷酸葡萄糖与阻遏蛋白结合后减弱或增强其对glpFKD操纵子表达的抑制作用，阐明伯氏疏螺旋体Rrp1/c-di-GMP经PlzA和阻遏蛋白在蜱或哺乳类不同宿主中不同碳源利用切换的分子机制，具有较高创新性和医学意义。

Borrelia burgdorferi must infect animals (e.g. rat and deer) and tick to complete its natural infection cycle. Recent literatures reported that glycerine and glucose are the major carbon sources for the spirochete in tick or mammal hosts, respectively, and thus, carbon source utilization switch is essential for spirochetal survival in different hosts. However, the switch mechanism remains unknown. Our previous study found that the Rrp1 (a c-di-GMP synthase), PlzA (a c-di-GMP-binding protein) and product of BB0693 gene (encoding the repressor protein RP0693) are involved in the expression regulation of glpFKD, the glycerine metabolism operon. In the present research project, we propose to demonstrate that the repressor protein RP0693 inhibits the expression of glpFKD operon by binding to the cis transcriptional control element in the 5’-UTR of glpFKD operon to repress glpFKD transcription, and that such repression can be released by interaction with c-di-GMP-bound PlzA protein, as well as by 3-phosphoglycerol- or 6-phosphoglucose-binding to RP0693. The aim of this project is to illuminate the molecular mechanism of c-di-GMP-dependent repressor protein mediating carbon source utilization switch of Borrelia burgdorferi during infection of different hosts, and such finding will be highly innovative with medical significance.