Streptococcus suisis an important cause of infectious diseases in young pigs. Little is known about the virulence factors or protective antigens ofS. suis. Recently, we have identified two proteins of the arginine deiminase system (ADS) ofS. suis, which were temperature induced and expressed on the streptococcal surface (N. Winterhoff, R. Goethe, P. Gruening, M. Rohde, H. Kalisz, H. E. Smith, and P. Valentin-Weigand, J. Bacteriol. 184:6768-6776, 2002). In the present study, we analyzed the complete ADS ofS. suis. Due to their homologies to the recently publishedS. gordoniiADS genes, the genes for arginine deiminase, ornithine carbamoyl-transferase, and carbamate kinase, which were previously designatedadiS,octS, andckS, respectively, were renamedarcA,arcB, andarcC, respectively. Our data revealed thatarcA,arcB, andarcCof theS. suisADS are transcribed from an operon (arcABCoperon). Additionally, putative ADS-associated genes were cloned and sequenced which, however, did not belong to thearcABCoperon. These were theflpSgene upstream of thearcABCoperon with homology to theflptranscription regulator ofS. gordoniiand thearcD,arcT,arcH, andargRgenes downstream of thearcABCoperon with high homologies to a putative arginine-ornithine antiporter, a putative dipeptidase ofS. gordonii, a putative β-N-acetylhexosaminidase ofS. pneumoniae, and a putative arginine repressor ofS. gordonii, respectively. The transcriptional start point of thearcABCoperon was determined, and promoter analysis provided evidence that multiple factors contribute to the regulation of the ADS. Thus, a putative binding site for a transcription regulator of the Crp/Fnr family, an ArgR-binding site, and twocis-acting catabolite response elements were identified in the promoter-operator region of the operon. Consistent with this, we could demonstrate that the ADS ofS. suisis inducible by arginine and reduced O₂tension and subject to carbon catabolite repression. Furthermore, comparing anarcAknockout mutant in which expression of the three operon-encoded proteins was abolished with the parental wild-type strain showed that thearcABCoperon ofS. suiscontributes to survival under acidic conditions.

Streptococcus suisis 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 that contribute to its virulence. Recently, we identified a new putative virulence factor inS. suis, the arginine deiminase system (ADS), an arginine catabolic enzyme system encoded by thearcABCoperon, which enablesS. suisto survive in an acidic environment. In this study, we focused on ArgR, an ADS-associated regulator belonging to the ArgR/AhrC arginine repressor family. Using anargRknockout strain we were able to show that ArgR is essential forarcABCoperon expression and necessary for the biological fitness ofS. suis. By cDNA expression microarray analyses and quantitative real-time RT-PCR we found that thearcABCoperon is the only gene cluster regulated by ArgR, which is in contrast to the situation in many other bacteria. Reporter gene analysis withgfpunder the control of thearcABCpromoter demonstrated that ArgR is able to activate thearcABCpromoter. Electrophoretic mobility shift assays with fragments of thearcABCpromoter and recombinant ArgR, and chromatin immunoprecipitation with antibodies directed against ArgR, revealed that ArgR interacts with thearcABCpromoterin vitroandin vivoby binding to a region from −147 to −72 bp upstream of the transcriptional start point. Overall, our results show that inS. suis, ArgR is an essential, system-specific transcriptional regulator of the ADS that interacts directly with thearcABCpromoterin vivo.

Type I interferons (IFN-I), such as IFN-α and IFN-β are important messengers in the host response against bacterial infections. Knowledge about the role of IFN-I in infections by nontuberculous mycobacteria (NTM) is limited. Here we show that macrophages infected with pathogens of the Mycobacterium avium complex produced significantly lower amounts of IFN-β than macrophages infected with the opportunistic pathogen M. smegmatis. To dissect the molecular mechanisms of this phenomenon, we focused on the obligate pathogen Mycobacterium avium ssp paratuberculosis (MAP) and the opportunistic M. smegmatis. Viability of both bacteria was required for induction of IFN-β in macrophages. Both bacteria induced IFN-β via the cGAS-STING-TBK1-IRF3/7-pathway of IFN-β activation. Stronger phosphorylation of TBK1 and higher amounts of extracellular bacterial DNA in the macrophage cytosol were found in M. smegmatis infected macrophages than in MAP infected macrophages. After intraperitoneal infection of mice, a strong Ifnb induction by M. smegmatis correlated with clearance of the bacteria. In contrast, MAP only induced weak Ifnb expression which correlated with bacterial persistence and increased number of granulomas in the liver. In mice lacking the type I interferon receptor we observed improved survival of M. smegmatis while survival of MAP was similar to that in wildtype mice. On the other hand, treatment of MAP infected wildtype mice with the IFN-I inducer poly(I:C) or recombinant IFN-β impaired the survival of MAP. This indicates an essential role of IFN-I in clearing infections by MAP and M. smegmatis. The expression level of IFN-I is decisive for transient versus persistent NTM infection.