Contribution of the RgfD Quorum Sensing Peptide to rgf Regulation and Host Cell Association in Group B Streptococcus

Abstract

<i>Streptococcus agalactiae</i> (group B <i>Streptococcus</i>; GBS) is a common inhabitant of the genitourinary and/or gastrointestinal tract in up to 40% of healthy adults; however, this opportunistic pathogen is able to breach restrictive host barriers to cause disease and persist in harsh and changing conditions. This study sought to identify a role for quorum sensing, a form of cell to cell communication, in the regulation of the fibrinogen-binding (<i>rgfBDAC</i>) two-component system and the ability to associate with decidualized endometrial cells in vitro. To do this, we created a deletion in <i>rgfD</i>, which encodes the putative autoinducing peptide, in a GBS strain belonging to multilocus sequence type (ST)-17 and made comparisons to the wild type. Sequence variation in the <i>rgf</i> operon was detected in 40 clinical strains and a non-synonymous single nucleotide polymorphism was detected in <i>rgfD</i> in all of the ST-17 genomes that resulted in a truncation. Using qPCR, expression of <i>rgf</i> operon genes was significantly decreased in the ST-17 <i>ΔrgfD</i> mutant during exponential growth with the biggest difference (3.3-fold) occurring at higher cell densities. Association with decidualized endometrial cells was decreased 1.3-fold in the mutant relative to the wild type and <i>rgfC</i> expression was reduced 22-fold in <i>ΔrgfD</i> following exposure to the endometrial cells. Collectively, these data suggest that this putative quorum sensing molecule is important for attachment to human tissues and demonstrate a role for RgfD in GBS pathogenesis through regulation of <i>rgfC</i>.