Abstract
Bacteria commonly exist in high cell density populations, making them prone to viral predation and horizontal gene transfer (HGT) through transformation and conjugation. To combat these invaders, bacteria possess an arsenal of defenses, such as CRISPR-Cas adaptive immunity. Many bacterial populations coordinate their behavior as cell density increases, using quorum sensing (QS) signaling. In this study, we demonstrate that QS regulation results in increased expression of the type I-E, I-F, and III-A CRISPR-Cas systems in Serratia cells in high-density populations. Strains unable to communicate via QS were less effective at defending against invaders targeted by any of the three CRISPR-Cas systems. Additionally, the acquisition of immunity by the type I-E and I-F systems was impaired in the absence of QS signaling. We propose that bacteria can use chemical communication to modulate the balance between community-level defense requirements in high cell density populations and host fitness costs of basal CRISPR-Cas activity.
[Display omitted]
•Quorum sensing regulates the type I-E, I-F, and III-A CRISPR-Cas systems in Serratia•SmaR represses cas gene and CRISPR expression in the absence of AHL signals•Both interference and adaptation are modulated by quorum sensing•Bacteria coordinate their defenses based on cell density and the risk of infection
Patterson et al. examined quorum sensing and the function of three CRISPR-Cas systems in Serratia. They discovered that bacteria can use chemical communication to coordinate CRISPR-Cas immune defenses at high cell densities.