Selective Maintenance of Multiple CRISPR Arrays Across Prokaryotes

Area of Science:

• Microbial immunology
• Bacterial and archaeal defense mechanisms
• Comparative genomics

Background:

• Prokaryotes face constant threats from viral pathogens.
• Diverse immune systems, including CRISPR, protect against infection.
• The presence of multiple, seemingly redundant CRISPR arrays in prokaryotes is puzzling.

Purpose of the Study:

• To investigate the evolutionary selection for multiple CRISPR arrays in prokaryotes.
• To explore hypotheses explaining the maintenance of redundant CRISPR systems.
• To theoretically analyze the trade-offs between memory span and learning speed in CRISPR immunity.

Main Methods:

• Comparative genomics analysis across prokaryotic genomes.
• Examination of CRISPR array distribution in the RefSeq database.
• Theoretical modeling of CRISPR array selection pressures.

Main Results:

• Approximately 28% of prokaryotic genomes in RefSeq contain multiple CRISPR arrays.
• On average, prokaryotes are under selection to maintain more than one CRISPR array.
• A theoretical trade-off between memory span and learning speed is proposed as a driver for multiple arrays.

Conclusions:

• Multiple CRISPR arrays are a common and selected-for trait in prokaryotes.
• This redundancy may represent a strategy to optimize immune memory and response speed.
• The findings suggest a sophisticated adaptive immune strategy in prokaryotes.