Type I CRISPR-Cas immunity primes type III spacer acquisition

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Microbial CRISPR-Cas systems exhibit diverse classes and subtypes.
• Type I (DNA-targeting) and Type III (RNA-targeting) systems frequently coexist but their interactions are poorly understood.
• The acquisition of functional spacers by Type III systems, especially those triggering cell death, remains unclear.

Purpose of the Study:

• To investigate the interplay between co-occurring Type I and Type III CRISPR-Cas systems in Prodigiosinella.
• To elucidate the mechanism of functional spacer acquisition in Type III systems.
• To understand the adaptive advantage conferred by the combined action of these systems.

Main Methods:

• Analysis of CRISPR-Cas system interactions in Prodigiosinella.
• Investigating spacer acquisition pathways for Type III systems.
• Assessing the impact of Type I interference on Type III system function and vice versa.

Main Results:

• Type I interference generates substrates that are acquired by the Type III adaptation machinery.
• Type III systems, while reducing Type I efficiency, contribute to plasmid loss and offer an advantage when Type I fails.
• Type I priming influences Type III spacer length and origin, with increased acquisition near Type I target sites.
• Type I clearance of invader DNA facilitates the retention of cytotoxic Type III spacers.

Conclusions:

• Type I and Type III CRISPR-Cas systems exhibit a synergistic relationship, with Type I facilitating Type III adaptation.
• Type III systems act as a backup defense mechanism, enhancing population-level protection in multi-system hosts.
• This interplay provides a more robust defense strategy against mobile genetic elements.