ArgR is an essential local transcriptional regulator of the arcABC-operon in Streptococcus suis and crucial for biological fitness in acidic environment

Streptococcus suis is one of the most important pathogens in pigs and can also cause severe infections in humans. Despite its clinical relevance very little is known about the factors contributing to its virulence. Recently, we identified a new putative virulence factor in Streptococcus suis, the arginine deiminase system (ADS), an arginine catabolic enzyme system encoded by the arcABC-operon, which enables Streptococcus suis to survive in acidic environment. In this study, we focused on ArgR, an ADS associated regulator belonging to the ArgR/AhrC arginine repressor family. Using an argR knock-out strain we could show that ArgR is essential for arcABC-operon expression and necessary for the biological fitness of Streptococcus suis. By cDNA expression microarray analyses and quantitative real time RT-PCR we found that the arcABC-operon is the only gene cluster regulated by ArgR, which is in contrast to many other bacteria. Reporter gene analysis with gfp under the control of the arcABC promoter demonstrated that ArgR is able to activate the arcABC promoter. Electrophoretic mobility shift assays with fragments of the arcABC promoter and recombinant ArgR, and chromatin immunoprecipitation with antibodies directed against ArgR revealed that ArgR interacts with the arcABC promoter in vitro and in vivo by binding to a region from -147 to 72 bp upstream of the transcriptional start point. Overall our results show that in Streptococcus suis ArgR is an essential, system specific transcriptional regulator of the ADS directly interacting with the arcABC promoter in vivo

Involvement of NF-κB and MAP-kinases in the transcriptional response of alveolar macrophages to Streptococcus suis

Interaction of Streptococcus suis with primary porcine alveolar macrophages was Studied using transcriptomics. Transcriptional response of macrophages to two different S. suis strains was studied: wild-type S10 that is resistant to phagocytosis, and its non-encapsulated mutant that is phagocytosed efficiently. The macrophages' transcriptional response was observed only after 60 min of incubation. Eleven genes were expressed significantly different between macrophages infected with streptococci and control mock-infected macrophages. These genes include IL-1-beta, MIP-2-alpha and TNF-alpha. When gene expression was studied as a function of time, transcriptional changes occurred in all macrophages independent of streptococci. The fold induction of induced genes however, was much stronger in macrophages incubated with the non-encapsulated S. suis strain that was phagocytosed. The genes that were higher induced due to S. suis suggest an innate immune response is induced in macrophages. Pathway analysis revealed that genes that are part of the putative MAP-kinase signal transduction system are over-represented among the regulated genes. Using an immortalized alveolar macrophage cell line it was shown that macrophages respond to interaction with S. suis by the translocation of NF-kappa B to the nucleus, independent of phagocytosis. This translocation subsequently induced expression of innate immune genes. This strongly suggests besides the MAP-kinase signaling pathway, NF-kappa B signaling is also induced upon interaction with S. suis. (C) 2009 Elsevier B.V. All rights reserved