Quorum sensing inhibits Type III-A CRISPR-Cas system activity through repressing positive regulators SarA and ArcR in Staphylococcus aureus

CRISPR-Cas is an adaptive immune system that protects prokaryotes from the invasion of foreign genetic elements. The components and immunity mechanisms of CRISPR-Cas have been extensively studied, but the regulation of this system in Staphylococci remains unclear. Here, we show that in the S. aureus Type III-A CRISPR-Cas system, the Pcas of 300 bp located in cas1 displays as a critical regulatory node that initiates the transcription of cas gene clusters. We discovered two transcriptional regulators, SarA and CRP-like ArcR, promote the expression and activity of the CRISPR-Cas system by directly binding to the novel promoter Pcas. Furthermore, we demonstrated that the cell-cell communication, known as quorum sensing (QS), inhibits the activity of CRISPR-Cas system by repressing the positive regulators SarA and ArcR. Bioinformatic analyses suggest that Pcas is conserved in many Type II and III CRISPR-Cas systems in Firmicutes. Our data reveal a new regulatory mechanism for QS-mediated repression of the Type III-A CRISPR-Cas system, which may allow S. aureus to acquire foreign genetic elements encoding antibiotic resistance or virulence factors specifically at high cell density.