Regulation of hyaluronic acid capsule biosythesis in Streptococcus pyogenes

Streptococcus pyogenes (Group A Streptococcus, GAS) is an important human pathogen that causes numerous diseases ranging from minor skin and throat infections such as impetigo and pharyngitis to life-threatening invasive infections such as streptococcal toxic syndrome and necrotizing fasciitis. Worldwide GAS infections account for more than 600 million cases of pharyngitis and more than 650,000 cases of invasive disease annually. Since the late 1980s, there has been a worldwide increase in invasive GAS disease. Although the pathogen is susceptible to antibiotic therapy, severe invasive GAS infections are often difficult to treat. Hyaluronic acid (HA) capsule is considered one of the major determinants of GAS virulence. Highly encapsulated GAS strains are associated with both invasive infections and outbreaks of acute rheumatic fever. GAS mutants lacking capsule are sensitive to neutrophil killing and have reduced virulence in murine model of GAS infection. In addition to its role in bacterial resistance to host defense attack, HA capsule mediates adherence and promotes GAS colonization of the pharynx. The enzymes involved in HA capsule biosynthesis are encoded by the hasABC operon. The transcription of the operon is negatively regulated by CovRS two-component regulatory system. Presence of spontaneous mutations in the CovRS has helped to explain wide variations in encapsulation among GAS strains. However some strains with intact CovRS also produce large amounts of capsule. Thus, it is possible that in addition to CovRS regulation, expression of HA capsule is controlled by an unknown mechanism. The primary objective of the proposed research is to understand the molecular mechanisms of HA capsule regulation. In our preliminary studies we identified a novel regulatory noncoding region that controls capsule operon transcription. We confirmed that the region is physiologically significant and is important for full virulence in mouse model of GAS invasive disease. Moreover, we found that the region is under strong selective pressure resulting in accumulation of spontaneous mutations in GAS clinical strains. It raises an intriguing possibility that the acquisition of mutations in this regulatory region might permit the pathogen to shift from one style to another. We propose to define this novel capsule regulation mechanism using advanced genetic and biochemical techniques. The results of this study will advance our understanding of the molecular basis of GAS invasive disease and may permit the development of novel therapeutic approaches to control the infection.