Analysis of the roles of NrdR and DnaB from Streptococcus pyogenes in response to host defense

Toxic shock syndrome caused by Streptococcus pyogenes (S. pyogenes) is a re-emerging infectious disease. Many virulence-associated proteins play important roles in its pathogenesis and the production of these proteins is controlled by many regulatory factors. CovS is one of the most important two-component sensor proteins in S. pyogenes, and it has been analyzed extensively. Our recent analyses revealed the existence of a transposon between covS and nrdR in several strains, and we speculated that this insertion has some importance. Hence, we examined the significances of the NrdR stand-alone regulator and DnaB, which is encoded by the gene located immediately downstream of nrdR in S. pyogenes infection. We established an nrdR-only knockout strain, and both nrdR and partial dnaB knockout strain. These established knockout strains exhibited a deteriorated response to H2 O2 exposure. nrdR and partial dnaB knockout strain was more easily killed by human polynuclear blood cells, but the nrdR-only knockout strain had no significant difference compared to wild type in contrast to the combined knockout strain. In addition, the mouse infection model experiment illustrated that nrdR and partial dnaB knockout strain, but not the nrdR-only knockout strain, was less virulent compared with the parental strain. These results suggest that DnaB is involved in response to host defense.