FUNCTIONAL ANALYSIS OF THE QUORUM-SENSING REGUALTED BACTERIOCIN OPERONS OF GROUP A STREPTOCOCCUS

Group A Streptococcus (GAS) is a Gram-positive human pathogen able to cause mild to highly invasive life-threatening infections. Previously, our group identified the streptococcal invasion locus (sil) which may be involved in GAS virulence¹. sil is a quorum-sensing-regulated locus which is activated by the autoinducer peptide SilCR through the two-component system SilA-SilB. In most of GAS strains the locus is missing or inactive. In this study, we identified a GAS strain (JS12) which possesses a naturally functional sil, namely able to sense and produce the autoinducer SilCR. Sequencing of this locus showed that it contains two operons that encode bacteriocin like peptides and cognate immunity proteins. Based on the homology of the bacteriocins to those of Streptococcus pneumoniae these operons were termed blpUop and blpJop. We showed that upon activation of the quorum sensing system, bacteriocins are produced and inhibit the growth of GAS JRS4 strain which does not possess sil. In addition, we identified one immunity protein against BlpJ. Most importantly, we showed that upon interaction with host cells, JS12 activates sil and produces bacteriocins that inhibit the growth of JRS4. These results imply that bacteriocins produced from sil are instrumental in cases of intraspecies competition during colonization of host cells.

Belotserkovsky, I., Baruch, M., Peer, A., Dov, E., Ravins, M., Mishalian, I., Persky, M., Smith, Y., and Hanski, E. (2009). Functional analysis of the quorum-sensing streptococcal invasion locus (sil). PLoS Pathog. 5,e1000651.