Group B Streptococcus Biofilm Regulatory Protein A Contributes to Bacterial Physiology and Innate Immune Resistance

Background. Streptococcus agalactiae (group B Streptococcus [GBS]) asymptomatically colonizes approximately 20% of adults; however, GBS causes severe disease in susceptible populations, including newborns, pregnant women, and elderly individuals. In shifting between commensal and pathogenic states, GBS reveals multiple mechanisms of virulence factor control. Here we describe a GBS protein that we named biofilm regulatory protein A (BrpA) on the basis of its homology with BrpA from Streptococcus mutans. Methods. We coupled phenotypic assays, RNA sequencing, human neutrophil and whole-blood killing assays, and murine infection models to investigate the contribution of BrpA to GBS physiology and virulence. Results. Sequence analysis identified BrpA as a LytR-CpsA-Psr enzyme. Targeted mutagenesis yielded a GBS mutant (Delta brpA) with normal ultrastructural morphology but a 6-fold increase in chain length, a biofilm defect, and decreased acid tolerance. GBS Delta brpA stimulated increased neutrophil reactive oxygen species and proved more susceptible to human and murine blood and neutrophil killing. Notably, the wild-type parent outcompeted Delta brpA GBS in murine sepsis and vaginal colonization models. RNA sequencing of Delta brpA uncovered multiple differences from the wild-type parent, including pathways of cell wall synthesis and cellular metabolism. Conclusions. We propose that BrpA is an important virulence regulator and potential target for design of novel antibacterial therapeutics against GBS.