A Cas12a Toolbox for Rapid and Flexible Group B Streptococcus Genomic Editing and CRISPRi.

Streptococcus agalactiae (group B Streptococcus; GBS) is a leading cause of neonatal sepsis and meningitis. Despite advances in molecular microbiology, GBS genome engineering remains laborious due to inefficient mutagenesis protocols. Here, we report a versatile and rapid Cas12a-based toolkit for GBS genetic manipulation. We developed two shuttle plasmids-pGBSedit for genome editing and pGBScrispri for inducible CRISPR interference-derived from an Enterococcus faecium system and optimized for GBS. Using these tools, we achieved targeted gene insertions, markerless deletions, and efficient, template-free mutagenesis via alternative end-joining repair. Furthermore, a catalytically inactive dCas12a variant enabled inducible gene silencing, with strand-specific targeting effects. The system demonstrated broad applicability across multiple GBS strains and minimal off-target activity, as confirmed by whole-genome sequencing. This Cas12a-based platform offers a rapid, flexible, and scalable approach to genetic studies in GBS, facilitating functional genomics and accelerating pathogenesis research.