Department of Paediatrics, Imperial College London, St. Mary's Campus, London W21PG, United Kingdom.
J Bacteriol. 2010 May;192(9):2414-23. doi: 10.1128/JB.01513-09. Epub 2010 Mar 5.
Clinical isolates of the porcine pathogen Actinobacillus pleuropneumoniae often form adherent colonies on agar plates due to expression of an operon, pgaABCD, encoding a poly-beta-1,6-N-acetyl-D-glucosamine (PGA) extracellular matrix. The adherent colony phenotype, which correlates with the ability to form biofilms on the surfaces of polystyrene plates, is lost following serial passage in broth culture, and repeated passage of the nonadherent variants on solid media does not result in reversion to the adherent colony phenotype. In order to investigate the regulation of PGA expression and biofilm formation in A. pleuropneumoniae, we screened a bank of transposon mutants of the nonadherent serovar 1 strain S4074(T) and identified mutations in two genes, rseA and hns, which resulted in the formation of the adherent colony phenotype. In other bacteria, including the Enterobacteriaceae, H-NS acts as a global gene regulator, and RseA is a negative regulator of the extracytoplasmic stress response sigma factor sigma(E). Transcription profiling of A. pleuropneumoniae rseA and hns mutants revealed that both sigma(E) and H-NS independently regulate expression of the pga operon. Transcription of the pga operon is initiated from a sigma(E) promoter site in the absence of H-NS, and upregulation of sigma(E) is sufficient to displace H-NS, allowing transcription to proceed. In A. pleuropneumoniae, H-NS does not act as a global gene regulator but rather specifically regulates biofilm formation via repression of the pga operon. Positive regulation of the pga operon by sigma(E) indicates that biofilm formation is part of the extracytoplasmic stress response in A. pleuropneumoniae.
猪病原体胸膜肺炎放线杆菌的临床分离株由于表达操纵子 pgaABCD，编码多-β-1,6-N-乙酰-D-葡萄糖胺（PGA）细胞外基质，常形成在琼脂平板上黏附的菌落。黏附菌落表型与在聚苯乙烯板表面形成生物膜的能力相关，在肉汤培养中连续传代后丢失，并且在固体培养基上多次传代非黏附变体不会导致回复到黏附菌落表型。为了研究胸膜肺炎放线杆菌中 PGA 表达和生物膜形成的调节，我们筛选了非黏附血清型 1 菌株 S4074(T)的转座子突变体库，并鉴定了两个基因 rseA 和 hns 的突变，导致形成黏附菌落表型。在其他细菌中，包括肠杆菌科，H-NS 作为全局基因调节剂，而 RseA 是细胞外应激反应 sigma 因子 sigma(E)的负调节剂。胸膜肺炎放线杆菌 rseA 和 hns 突变体的转录谱分析表明，sigma(E)和 H-NS 均可独立调节 pga 操纵子的表达。在没有 H-NS 的情况下，pga 操纵子的转录从 sigma(E)启动子位点起始，并且 sigma(E)的上调足以取代 H-NS，从而允许转录进行。在胸膜肺炎放线杆菌中，H-NS 不作为全局基因调节剂，而是通过抑制 pga 操纵子特异性地调节生物膜形成。sigma(E)对 pga 操纵子的正调控表明生物膜形成是胸膜肺炎放线杆菌细胞外应激反应的一部分。
