Expression of Adhesive Pili and the Collagen-Binding Adhesin Ace Is Activated by ArgR Family Transcription Factors in Enterococcus faecalis.

In E. faecalis OG1RF, disruption of the ahrC gene encoding a predicted ArgR family transcription factor results in a severe defect in biofilm formation in vitro, as well as significant attenuation of virulence in multiple experimental infection models. Using RNA-seq, we observed ahrC-dependent changes in expression of over 20 genes. AhrC-repressed genes included predicted determinants of arginine catabolism and several other metabolic genes and predicted transporters, while AhrC-activated genes included determinants involved in production of surface protein adhesins. Most notably, the structural and regulatory genes of the ebp locus encoding adhesive pili were positively regulated, as well as the ace gene, encoding a collagen binding adhesin. Using lacZ transcription reporter fusions, we determined that ahrC and a second argR transcription factor gene, argR2, both function to activate expression of ebpR, which directly activates transcription of the pilus structural genes. Our data suggest that in wild-type E. faecalis, the low levels of EbpR limit expression of pili, and that biofilm biomass is also limited by the amount of pili expressed by the bacteria. Expression of ace is similarly activated by AhrC and ArgR2, but ace expression is not dependent on EbpR. Our results demonstrate the existence of novel regulatory cascades controlled by a pair of ArgR family transcription factors that may function as a heteromeric protein complex. Used RNA-seq to identify the ahrC regulon of E. faecalis OG1RF under both biofilm and planktonic growth conditions in M9-YE using the CDC biofilm reactor (CBR). We compared the transcriptomes of wild-type OG1RF and an isogenic derivative with in-frame deletion mutant of ahrC (D983). Also carried out RNA-seq analysis of wild-type OG1RF and the ΔahrC (D983) derivative in liquid cultures grown in BHI medium. For each strain and experiment, RNA libraries from two biological replicates were sequenced.