Cysteine protease SpeB expression in group A streptococci is influenced bythe nutritional environment but SpeB does not contribute to obtaining essential nutrients

Group A streptococcal (GAS) cysteine protease is a major virulence factor i nvolved in the pathogenesis of purulent and invasive infections. The secret ed enzyme cleaves a number of different bacterial and host proteins which c ould contribute to different stages of the infective processes. It has been proposed that, among these functions, SpeB plays a role in obtaining nutri ents during late growth phases. In the present study, speB mutants of vario us GAS serotypes were found to exhibit unaltered growth characteristics in several complex and chemically defined media (CDM). When amino acid-deplete d CDM was prepared, neither SpeB activity on whole proteins added to the me dium during incubation nor the addition of SpeB;digested proteins was able to support bacterial growth. SpeB also was unable to liberate iron from iro n-containing protein sources added to iron-deficient CDM. However, SpeB lev els in culture supernatants changed in response to the protein and glucose content of the media. Using a speB promoter-luciferase reporter, speB expre ssion levels were found to correspond to peptide concentrations in the cult ure media. The effect appeared to be specific for peptides since addition o f peptides derived from various proteins had an affect on expression, while addition of the whole proteins had no effect. Addition of glucose to CDM h ad no effect on SpeB expression, while glucose addition to complex medium d ecreased speB expression. Overall, SpeB did not appear to be directly invol ved in providing the bacteria with nutritional factors but expression of th e speB gene responded to ratios of peptides and carbohydrates in the cultur e medium.