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Substrate Generation for Endonucleases of CRISPR/Cas Systems
Published on: September 8, 2012
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Characterization and evolution of Salmonella CRISPR-Cas systems
Nikki Shariat1, Ruth E Timme2, James B Pettengill2
11Department of Food Science, Center for Molecular Immunology and Infectious Disease and Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802, USA.
Microbiology (Reading, England)
|February 17, 2017
Summary
Salmonella CRISPR-Cas systems are highly conserved but no longer provide adaptive immunity. Their genetic integrity suggests a potential alternative function beyond defense against invasive elements.
Area of Science:
- Microbiology
- Genomics
- Molecular Biology
Background:
- Prokaryotic CRISPR-Cas systems offer adaptive immunity against foreign genetic material.
- These systems comprise cas genes, CRISPR arrays with spacers and repeats, and leader sequences.
Purpose of the Study:
- To analyze the CRISPR-Cas systems in over 600 Salmonella isolates from four prevalent serovars.
- To investigate the conservation, evolution, and potential function of these systems in Salmonella.
Main Methods:
- In-depth sequence analysis of CRISPR-Cas loci in Salmonella isolates.
- Comparative genomics to assess conservation across serovars and identify sequence variations.
Main Results:
- CRISPR-Cas features are highly conserved in Salmonella, with CRISPR1 being more conserved than CRISPR2.
- Spacer composition is serovar-specific, but evidence for recent adaptive immune events is minimal (12% matches to exogenous DNA).
- High nucleotide identity in cas operons suggests historical immune activity, with inactive loci showing remarkable conservation, contradicting typical degeneration.
Conclusions:
- Salmonella CRISPR-Cas systems appear to be non-immunogenic, having ceased adaptive events.
- The exceptional conservation of these loci implies a potential alternative, non-immune function in Salmonella.
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