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Abundance of the Subunit of RNA Polymerase Is Linked to the Virulence of Streptococcus agalactiae

Ravin Seepersaud, Rachel H. V. Needham, Cathy S. Kim, and Amanda L. Jones^*

Department of Pediatrics, Division of Infectious Disease, Children's Hospital and Regional Medical Center and University of Washington, Seattle, Washington, 98109

Received 15 September 2005/ Accepted 20 December 2005

Group B streptococcus (GBS) remains a major cause of morbidity and mortality among newborn children. The bacterium is a commensal organism colonizing the rectum and the gastrointestinal and urogenital tracts of adults, but it can be transmitted to neonates by an ascending infection of the maternal genital tract or during parturition. We previously reported that a transposon insertion disrupting rpoE resulted in the decreased survival of the mutant in the neonatal rat sepsis model of GBS infection. rpoE encodes the protein, a subunit of RNA polymerase (RNAP) that has been characterized in Bacillus species. In this study, we confirm the association of the protein with purified GBS RNAP and show that it is expressed in strains representing all nine serotypes. Flow cytometric analysis of a reporter strain containing a transcriptional fusion of the rpoE promoter to gfp revealed that, in vitro, this gene is continuously expressed. Analysis of expression in the transposon mutant by quantitative Western blotting revealed a 10-fold reduction in relative abundance (which was linked to the attenuation in virulence that was observed for this mutant) compared to that for the wild-type strain. These data suggest that a minimum intracellular concentration of is necessary for this organism to cause disease.

Present address: Rosetta Inpharmatics, 401 Terry Avenue N, Seattle, WA 98109.

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