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Journal of Bacteriology, March 2009, p. 1509-1518, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01213-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Bacteriocin Activity of Streptococcus pneumoniae Is Controlled by the Serine Protease HtrA via Posttranscriptional Regulation{triangledown}

Suzanne Dawid,1* Michael E. Sebert,1,2 and Jeffrey N. Weiser2,3

Department of Pediatrics, The Children's Hospital of Philadelphia,1 Department of Pediatrics,2 Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania3

Received 29 August 2008/ Accepted 10 December 2008

The blp locus of a type 6A strain of Streptococcus pneumoniae encodes a two-peptide bacteriocin, pneumocin MN, which mediates intraspecies competition during mouse nasopharyngeal colonization. This locus is regulated by a quorum-sensing mechanism consisting of a dedicated two-component regulatory system and a peptide pheromone. Like most clinical isolates, this type 6A strain can be separated into opaque and transparent colony variants, each playing a different role during pneumococcal infection. In this study, we show that the blp locus is differentially regulated at the posttranscriptional level in pneumococcal opacity variants. Transparent and opaque variants produce equivalent amounts of blpMNPO transcript when stimulated with a synthetic pheromone, but transparent variants have no pneumocin MN-mediated inhibitory activity while opaque variants produce large zones of inhibitory activity. The differential regulation in opacity variants is driven by the two-component regulatory system CiaRH via its regulation of the serine protease HtrA. Transparent mutants deficient in CiaH or HtrA show increased pneumocin MN-mediated inhibition. In addition, these mutants demonstrate alterations in their dose response to a synthetic peptide pheromone, suggesting that HtrA activity impacts pneumocin MN production at the level of signaling. This, in addition to its known effects on competence, suggests that HtrA is a pleiotropic regulator whose protease activity affects several important bacterial pathways. The complex regulation of pneumocins may allow the pneumococcus to reserve the secretion of active peptides for situations where the benefit of their inhibitory activity outweighs the cost of their production.

* Corresponding author. Present address: 1150 W. Medical Center Drive, 7510C MSRBI, Ann Arbor, MI 48109. Phone: (734) 764-6260. Fax: 734-936-7083. E-mail: sdawid{at}umich.edu

{triangledown} Published ahead of print on 19 December 2008.

Journal of Bacteriology, March 2009, p. 1509-1518, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01213-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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