Inter-viral conflicts that exploit host CRISPR immune systems of Sulfolobus

Area of Science:

• Microbiology
• Virology
• Molecular Biology

Background:

• The CRISPR-Cas adaptive immune system provides defense against foreign genetic elements in prokaryotes.
• Sulfolobus islandicus REY15A utilizes CRISPR immunity against viral infections.

Purpose of the Study:

• To investigate the impact of coinfection with Sulfolobus viruses SMV1 and STSV2 on the CRISPR immune system of Sulfolobus islandicus REY15A.
• To elucidate the mechanisms of viral resistance and adaptation within the CRISPR-Cas system.

Main Methods:

• Coinfection experiments with Sulfolobus viruses.
• Analysis of CRISPR spacer acquisition.
• Isolation and characterization of viral variants.
• DNA-binding assays for viral proteins.

Main Results:

• Coinfection with SMV1 and STSV2 induced hyperactive spacer acquisition from STSV2, leading to STSV2 loss but SMV1 resistance.
• A SMV1 variant lacking ORF114 facilitated spacer acquisition from SMV1 in a CRISPR-resistant host.
• Evidence for CRISPR locus size limits, growth retardation, random protospacer selection, and reversible spacer uptake was observed.

Conclusions:

• SMV1 activates CRISPR adaptation while resisting interference, but a specific variant can overcome this.
• Viral protein ORF114 plays a role in SMV1's DNA interaction and immune evasion.
• The study provides insights into CRISPR-virus interactions and viral immune evasion strategies.