INSERTIONAL INACTIVATION OF STREPTOLYSIN-S EXPRESSION IS ASSOCIATED WITH ALTERED RIBOFLAVIN METABOLISM IN STREPTOCOCCUS-PYOGENES

Transposon Tn916 mutagenesis was used to create a mutant of Streptococ cus pyogenes M type 3, designated ISS417, in which the ability to prod uce streptolysin S (SLS) and several other exoproteins was impaired. C oncomitantly, the mutant became dependent upon riboflavin for growth a nd was able to grow in Todd Hewitt broth (THB) when supplemented with riboflavin or riboflavin-rich yeast extract. The parent strain was app arently able to utilize THB-derived components as a substitute for rib oflavin, while the mutant was not. Although the parent strain grew wel l in synthetic medium, it was unable to produce SLS, except when it wa s supplemented with a small amount of THB. Thus, a component of THB wa s able to ''trigger'' SLS formation in the parent strain. The mutant g rew well in this medium, but was unable to produce SLS even when it wa s supplemented with THB. Southern hybridization analysis revealed that ther ISS417 mutant harbours a single transposon insertion in its chro mosome. Phage transduction experiments showed that the riboflavin depe ndency and the inability to make SLS phenotypes are co-transducible. T he pleotrophic properties of the ISS417 mutant differ from those repor ted for insertional inactivation of the mga locus which regulates prod uction of a number of surface proteins in S. pyogenes and the sar locu s which regulates production of a number of exoproteins in Staphylococ cus aureus. In view of the possibility that there exist a genetic link age between the riboflavin biosynthetic pathway and expression of the oxygen-stable SLS, we hypothesize that SLS has a role in the growth ec onomy of S. pyogenes. (C) 1997 Academic Press Limited.