外环境压力对福氏志贺菌荚膜异多糖酸合成调节子转录的影响

荚膜异多糖酸合成调节子(regulator of colanic acid capsule synthesis,Rcs)对大肠埃希菌适应外环境压力具有重要调控功能,但其在志贺菌中的功能尚未见报道。为探索外环境压力对福氏志贺菌Rcs编码基因rcs转录水平的影响,本研究采用核苷酸序列比对及蛋白结构域预测等生物信息学方法分析福氏志贺菌的Rcs编码基因簇rcsBDC,利用实时定量聚合酶链反应(quantitative real-time polymerase chain reaction,qRT-PCR),对该菌不同生长时期的rcsB、rcsD、rcsC基因转录水平进行分析,并检测在不同pH值培养基、渗透压条件下的基因转录水平。结果显示,福氏志贺菌rcsBDC在培养5～6 h(对数中期)时转录水平较高,8～10 h(稳定期)时转录水平较低(P<0.001);10 h时,rcsB和rcsD在酸性、渗透压条件下的转录水平均显著高于正常条件下的转录水平(P<0.05)。结果提示,外环境刺激可提高福氏志贺菌在稳定期的rcsB和rcsD转录水平,为志贺菌适应胃肠道酸性、渗透压环境的机制研究提供了一定理论基础。     

Genetic evidence of distinct physiological regulation mechanisms in the sigma(54) Pu promoter of Pseudomonas putida

The activity of the toluene-responsive sigma(54) Pu promoter of the pWW0 TOL plasmid of Pseudomonas putida is down-regulated in vivo during exponential growth in rich medium and also by the presence of glucose in the culture. Although the Pu promoter already performs poorly during log growth in minimal medium when amended with casamino acids, the addition of glucose further decreased by two- to threefold the accumulation of beta-galactosidase in a Pu-lacZ reporter P. putida strain. Since Pu was still down-regulated during exponential growth regardless of glucose addition, it appeared that the carbohydrate separately influenced promoter activity. This notion was supported by the growth-dependent induction pattern of Pu in a ptsN mutant of P. putida, the loss of which makes Pu no longer responsive to repression by glucose. On the other hand, overexpression of the sigma factor sigma(54), known to partially alleviate the exponential silencing of the promoter, did not affect glucose inhibition of Pu. These data indicated that exponential silencing and carbon source-dependent repression are two overlapping but genetically distinguishable mechanisms that adapt Pu to the physiological status of the cells and nutrient availability.     

痢疾杆菌体内诱导基因筛选方法的建立

分别用氯霉素乙酰转移酶基因(cat)和天冬氨酸半醛脱氢酶基因(asd)作为报告基因,用小鼠肺感染模型和HeLa细胞侵袭模型来试验筛选痢疾杆菌体内诱导基因的可行性。结果表明,以asd为报告基因,用HeLa细胞侵袭试验作为筛选模型,可成功地用于筛选痢疾杆菌的体内诱导基因。     

Activation of the CDC42 effector N-WASP by the Shigella flexneri IcsA protein promotes actin nucleation by Arp2/3 complex and bacterial actin-based motility.

To propel itself in infected cells, the pathogen Shigella flexneri subverts the Cdc42-controlled machinery responsible for actin assembly during filopodia formation. Using a combination of bacterial motility assays in platelet extracts with Escherichia coli expressing the Shigella IcsA protein and in vitro analysis of reconstituted systems from purified proteins, we show here that the bacterial protein IcsA binds N-WASP and activates it in a Cdc42-like fashion. Dramatic stimulation of actin assembly is linked to the formation of a ternary IcsA-N-WASP-Arp2/3 complex, which nucleates actin polymerization. The Arp2/3 complex is essential in initiation of actin assembly and Shigella movement, as previously observed for Listeria monocytogenes. Activation of N-WASP by IcsA unmasks two domains acting together in insertional actin polymerization. The isolated COOH-terminal domain of N-WASP containing a verprolin-homology region, a cofilin-homology sequence, and an acidic terminal segment (VCA) interacts with G-actin in a unique profilin-like functional fashion. Hence, when N-WASP is activated, its COOH-terminal domain feeds barbed end growth of filaments and lowers the critical concentration at the bacterial surface. On the other hand, the NH(2)-terminal domain of N-WASP interacts with F-actin, mediating the attachment of the actin tail to the bacterium surface. VASP is not involved in Shigella movement, and the function of profilin does not require its binding to proline-rich regions.