A compact Cascade-Cas3 system for targeted genome engineering

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• CRISPR-Cas systems are powerful gene-editing tools.
• Existing Cas9 and Cas12a enzymes are limited in creating large genomic deletions.

Purpose of the Study:

• To develop a CRISPR-Cas system for efficient large DNA deletions in bacteria.
• To engineer bacterial strains for synthetic biology and genome reduction.

Main Methods:

• Utilized a Type I-C Cascade-Cas3 system for targeted genome engineering in bacteria.
• Employed a single CRISPR RNA to guide Cas3 for DNA cleavage, creating large deletions (7-424 kb).
• Exploited bidirectional deletion generation by Cas3 to reduce the Pseudomonas aeruginosa genome.

Main Results:

• Achieved near-100% efficiency in generating large deletions in Pseudomonas aeruginosa.
• Cas3 system outperformed Cas9, which produced only small deletions and point mutations.
• Successfully reduced the P. aeruginosa genome by 13.5% (837 kb) using Cas3-mediated deletions.
• Demonstrated efficient specification of deletion boundaries using homology-directed repair with Cascade-Cas3.
• Showcased a transferable 'all-in-one' vector functional across multiple bacterial species (E. coli, P. syringae, K. pneumoniae).

Conclusions:

• The Type I-C Cascade-Cas3 system (PaeCas3c) enables efficient and precise large genomic deletions in bacteria.
• This technology has significant applications in synthetic biology, genome minimization, and targeted removal of genomic regions.
• The developed system offers a versatile and efficient approach for bacterial strain manipulation.