CRISPR-AsCas12a and dAsCas12a-Mediated Gene Knockout and Knockdown in Clostridioides difficile.

Clostridioides difficile (C. difficile) is a leading cause of antibiotic-associated diarrhea and severe colitis, yet its genetic manipulation has long been constrained by low DNA transfer efficiency and limited recombination systems. Recent advances in CRISPR-based technologies have revolutionized the genetic toolkit for this pathogen, enabling precise genome editing and transcriptional regulation. Among CRISPR nucleases, Cas12a offers distinct advantages over Cas9 for bacterial applications, including a smaller size, T-rich PAM recognition, single-crRNA requirement, and reduced toxicity, which enhances conjugation efficiency in genetically recalcitrant organisms. AsCas12a-based platforms have enabled large fragment deletions, multiplex editing, and rapid generation of marker-free mutants in C. difficile. Complementing these nuclease-active systems, nuclease-deactivated variants (dCas9 or dAsCas12a) support CRISPR interference (CRISPRi)-a reversible, tunable approach for transcriptional repression without altering genomic sequences. Compared to traditional mutagenesis, CRISPRi greatly accelerates functional genomics by enabling high-throughput screening and drug target discovery. Together, our lab has independently developed CRISPR-AsCas12a-mediated genome editing and dAsCas12a-based CRISPRi tools, providing complementary strategies to overcome longstanding genetic barriers in C. difficile. These tools open new avenues for system-level interrogation of virulence, antibiotic resistance, and host-pathogen interactions.