Protospacer-Adjacent Motif Specificity during Clostridioides difficile Type I-B CRISPR-Cas Interference and...

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• CRISPR-Cas systems provide prokaryotes with adaptive immunity against foreign nucleic acids.
• Clostridioides difficile, a human enteropathogen, possesses a CRISPR-Cas system, but its adaptation and interference mechanisms remain poorly understood.
• Bacterial type I-B CRISPR-Cas systems lack detailed studies regarding their adaptation processes.

Purpose of the Study:

• To investigate the adaptation process and sequence requirements of the CRISPR-Cas system in Clostridioides difficile.
• To provide the first experimental evidence for adaptation in a bacterial type I-B CRISPR-Cas system.
• To define the protospacer adjacent motif (PAM) for efficient interference and understand the link between adaptation and interference.

Main Methods:

• Overexpression of the C. difficile CRISPR-Cas adaptation module to induce new spacer acquisition.
• Protospacer adjacent motif (PAM) library experiments to determine sequence requirements for interference.
• Plasmid conjugation efficiency assays to assess CRISPR-Cas system activity.

Main Results:

• The C. difficile type I-B CRISPR-Cas system acquires new spacers upon adaptation module overexpression, primarily from plasmids and specific genomic regions.
• The system requires a YCN consensus PAM for efficient interference.
• A functional link was identified between adaptation and interference, with newly acquired spacers originating from sequences associated with a CCN PAM.

Conclusions:

• This study provides the first experimental evidence of adaptation in a type I-B CRISPR-Cas system within Clostridioides difficile.
• The findings reveal the sequence requirements (YCN PAM) for interference and a link to the adaptation process.
• Understanding these mechanisms is crucial for CRISPR-based genome editing applications and developing therapeutics against C. difficile infections.