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Prophages are associated with extensive, tolerated CRISPR-Cas auto-immunity
- Publication Year :
- 2020
-
Abstract
- CRISPR-Cas systems require discriminating self from non-self DNA during adaptation and interference. Yet, multiple cases have been reported of bacteria containing self-targeting spacers (STS), i.e. CRISPR spacers targeting protospacers on the same genome. STS may reflect potential auto-immunity as an unwanted side effect of CRISPR-Cas defense, or a gene regulatory mechanism. Here we investigated the incidence, distribution, and evasion of STS in over 100,000 bacterial genomes. We found STS in all CRISPR-Cas types and in one fifth of all CRISPR-carrying bacteria. Notably, up to 40% of I-B and I-F CRISPR-Cas systems contained STS. We observed that STS-containing genomes almost always carry a prophage and that STS map to prophage regions in more than half of the cases. Despite carrying STS, genetic deterioration of CRISPR-Cas systems appears to be rare, suggesting a level of tolerance to STS by other mechanisms such as anti-CRISPR proteins and target mutations. We propose a scenario where it is common and perhaps beneficial to acquire an STS against a prophage, and this may trigger more extensive STS buildup by primed spacer acquisition in type I systems, without detrimental autoimmunity effects. The mechanisms of auto-immunity evasion create tolerance to STS-targeted prophages, and contribute both to viral dissemination and bacterial diversification.
Details
- Language :
- English
- Database :
- OpenAIRE
- Accession number :
- edsair.dedup.wf.001..b9d09d025395e5374ec3afd598013661