Characterization of CRISPR-Cas systems.

Unlabelled: is a diverse genus among lactobacilli with phenotypes that reflect adaptation to various hosts. CRISPR-Cas systems are highly prevalent within lactobacilli, and , the most abundant species of , possesses both DNA- and RNA-targeting CRISPR-Cas systems. In this study, we explore the presence and functional properties of I-B, I-C, I-E, II-A, and III-A CRISPR-Cas systems in over 500 genomes, emphasizing systems found in . We examined the I-E, II-A, and III-A CRISPR-Cas systems of two strains and observed occurrences of split genes and differences in CRISPR RNA maturation in native hosts. This prompted testing of the single Cas9 and multiprotein Cascade and Csm CRISPR-Cas effector complexes in a cell-free context to demonstrate the functionality of these systems. We also predicted self-targeting spacers within CRISPR-Cas systems and found that nearly a third of genomes possess unique self-targeting spacers that generally target elements other than prophages. With these two strains, we performed prophage induction coupled with RNA sequencing and discovered that the prophages residing within these strains are inducible and likely active elements, despite targeting by CRISPR-Cas systems. These findings deepen our comprehension of CRISPR-Cas systems in , further elucidating their relationship with associated prophages and providing a functional basis for the repurposing of these Cas effectors for bacterial manipulation.

Importance: is a diverse bacterial species widely used in the food and dietary supplement industries. In this study, we investigate the occurrence and diversity of their adaptive immune systems, CRISPR-Cas, in over 500 genomes. We establish their function and provide insights into their role in the interplay between the bacterial host and the predatory phages that infect them. Such findings expand our knowledge about these important CRISPR-Cas immune systems widespread across the bacterial tree of life and also provide a technical basis for the repurposing of these molecular machines for the development of molecular biology tools and the manipulation and engineering of bacteria and other life forms.