Bugrysheva Julia V, Bryksin Anton V, Godfrey Henry P, Cabello Felipe C
Department of Microbiology and Immunology, Basic Science Building, New York Medical College, Valhalla, NY 10595, USA.
Infect Immun. 2005 Aug;73(8):4972-81. doi: 10.1128/IAI.73.8.4972-4981.2005.
The global transcriptional regulator (p)ppGpp (guanosine-3'-diphosphate-5'-triphosphate and guanosine-3',5'-bisphosphate, collectively) produced by the relA and spoT genes in Escherichia coli allows bacteria to adapt to different environmental stresses. The genome of Borrelia burgdorferi encodes a single chromosomal rel gene (BB0198) (B. burgdorferi rel [rel(Bbu)]) homologous to relA and spoT of E. coli. Its role in (p)ppGpp synthesis, bacterial growth, and modulation of gene expression has not been studied in detail. We constructed a rel(Bbu) deletion mutant in an infectious B. burgdorferi 297 strain and isolated an extrachromosomally complemented derivative of this mutant. The mutant did not synthesize rel(Bbu) mRNA, Rel(Bbu) protein, or (p)ppGpp. This synthesis was restored in the complemented derivative, confirming that rel(Bbu) is necessary and sufficient for (p)ppGpp synthesis and degradation in B. burgdorferi. The rel(Bbu) mutant grew well during log phase in complete BSK-H but reached lower cell concentrations in the stationary phase than the wild-type parent, suggesting that (p)ppGpp may be an important factor in the ability of B. burgdorferi to adapt to stationary phase. Deletion of rel(Bbu) did not eliminate the temperature-elicited OspC shift, nor did it alter bmp gene expression or B. burgdorferi antibiotic susceptibility. Although deletion of rel(Bbu) eliminated B. burgdorferi virulence for mice, which was not restored by complementation, we suggest that rel(Bbu)-dependent accumulation of (p)ppGpp may be important for in vivo survival of this pathogen.
由大肠杆菌中relA和spoT基因产生的全局转录调节因子（p）ppGpp（鸟苷-3'-二磷酸-5'-三磷酸和鸟苷-3'，5'-二磷酸的统称）可使细菌适应不同的环境压力。伯氏疏螺旋体的基因组编码一个与大肠杆菌relA和spoT同源的单一染色体rel基因（BB0198）（伯氏疏螺旋体rel [rel（Bbu）]）。其在（p）ppGpp合成、细菌生长和基因表达调控中的作用尚未得到详细研究。我们在具有感染性的伯氏疏螺旋体297菌株中构建了rel（Bbu）缺失突变体，并分离出该突变体的染色体外互补衍生物。该突变体不合成rel（Bbu）mRNA、Rel（Bbu）蛋白或（p）ppGpp。这种合成在互补衍生物中得以恢复，证实rel（Bbu）对于伯氏疏螺旋体中（p）ppGpp的合成和降解是必要且充分的。rel（Bbu）突变体在完全BSK-H培养基的对数期生长良好，但在稳定期的细胞浓度低于野生型亲本，这表明（p）ppGpp可能是伯氏疏螺旋体适应稳定期能力的一个重要因素。rel（Bbu）的缺失并未消除温度诱导的OspC转变，也未改变bmp基因表达或伯氏疏螺旋体的抗生素敏感性。虽然rel（Bbu）的缺失消除了伯氏疏螺旋体对小鼠的毒力，且互补并未恢复该毒力，但我们认为rel（Bbu）依赖的（p）ppGpp积累可能对该病原体的体内存活很重要。
