Mobile CRISPR/Cas-mediated bacteriophage resistance in Lactococcus lactis

Area of Science:

• Microbiology
• Bacteriology
• Genetics

Background:

• Lactococcus lactis is a key microbe in food fermentation and potential therapeutics.
• L. lactis possesses plasmid-encoded systems for bacteriophage defense.
• CRISPR/Cas systems, a major microbial immunity mechanism, were previously absent in published L. lactis genomes.

Purpose of the Study:

• To identify and characterize novel CRISPR/Cas systems in L. lactis.
• To investigate the function and transferability of a newly discovered CRISPR/Cas system.
• To assess the potential of this system for enhancing phage resistance in industrial L. lactis strains.

Main Methods:

• Genomic analysis of L. lactis strains.
• PCR screening for known CRISPR/Cas types (I and II).
• Discovery and characterization of a novel Type III CRISPR/Cas system on a self-transmissible plasmid.
• Conjugal transfer experiments to assess plasmid mobility.

Main Results:

• A novel, plasmid-encoded, Type III CRISPR/Cas system was identified in L. lactis.
• The system confers resistance against problematic lactococcal phages.
• The 62.8-kb plasmid carrying the CRISPR/Cas system is conjugally transferable to other L. lactis strains.
• Spacer content could be engineered for modified targeting.

Conclusions:

• This discovery introduces a new CRISPR/Cas system to L. lactis, expanding known phage defense mechanisms.
• The self-transmissible nature of the plasmid facilitates its spread and application in industrial settings.
• This system offers a promising tool for enhancing phage resistance and preventing undesirable gene acquisition in L. lactis.