Bacteria exploit viral dormancy to establish CRISPR-Cas immunity

Area of Science:

• Microbiology
• Molecular Biology
• Immunology

Background:

• CRISPR-Cas systems provide adaptive immunity in prokaryotes via spacer acquisition.
• The mechanism of acquiring immunity during initial phage infection, especially without prior defense, is poorly understood.

Purpose of the Study:

• To investigate how bacteria establish CRISPR-Cas immunity during phage infection.
• To explore the role of the lysogenic life cycle in CRISPR-Cas spacer acquisition.
• To understand how bacteria manage self-targeting of prophages.

Main Methods:

• Comparative analysis of immunization rates in lysogenic versus lytic phage infections.
• Investigation of spacer acquisition targeting intracellular prophages.
• Assessment of Cas9 activity on chromosomal prophages.

Main Results:

• Lysogeny significantly enhances CRISPR-Cas immunization rates compared to lysis.
• Bacteria acquire spacers targeting prophages, leading to prophage curing via Cas9.
• This self-targeting mechanism prevents autoimmunity in immunized bacteria.

Conclusions:

• The lysogenic life cycle is crucial for establishing CRISPR-Cas immunity against phages.
• Bacteria can utilize CRISPR-Cas to eliminate internal prophages, a key self-defense mechanism.
• Spacer acquisition during lysogeny explains the prevalence of temperate phage targets in natural isolates.